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Lionel Sear

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16Instructables65,426Views43CommentsSouth west England
I am a retired analytical chemist living with my wife Cynthia in Cornwall, south west England. I have held the UK radio amateur call sign G3PPT since 1961. I have been interested in computing since the days of the Commodore PET and have written some (very bad) programs associated with amateur radio in C and C++. Another hobby which we both share is the chasing up and photographing of film locations for the website www.reelstreets.com.

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Solar Contest 2016
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  • The 31 Year LED Flasher for Model Lighthouses Etc..

    Hello MattIt probably would work but the LED will be 'on' to a degree most of the time and the current consumption will rise to low milliAmps rather than low microAmps. A period on the breadboard will be needed to see if there is any advantage.

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  • How to Run a Battery Electric Clock on Solar Power--Part I

    Hi WeirdAlWalker. I have a much simpler way of doing this now so give me a day or twp to prepare a diagram and I'll be back. Kind regards.Lionel

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  • The 31 Year LED Flasher for Model Lighthouses Etc..

    That's great John and thanks for letting me know and yes, please send the Gerber files when they become available.As for the capacitor I have used both non polar electrolytic and ceramic in different versions. Ceramic capacitors of the size required for long time periods will probably have enormous temperature coefficients but we can overlook the resultant varying flash rate. In such a high impedance circuit low leakage is most important.

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  • The 31 Year LED Flasher for Model Lighthouses Etc..

    Hi JohnI do not know what facilities you have but I find that a plug board such as the one shown in Step 4 is extremely helpful. This would enable you to get the oscillator running and then work logically on from there.Plug your IC in and then using short lengths of PVC covered single wire, (such as that found in telephone cable,) connect negative (7) to ground and positive (14) to the positive rail. Connect the gate inputs 1 and 2, 5 and 6, 8 and 9, 11 and 12 together and to ground. Logic IC's do funny things when the gates are left floating. Do not worry about the resistor in the positive line to the IC at this stage.Because you do not have a high impedance voltmeter you will need a high impedance indicator circuit and I have attached a simple circuit which uses the 2N7000 FET. If y…

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    Hi JohnI do not know what facilities you have but I find that a plug board such as the one shown in Step 4 is extremely helpful. This would enable you to get the oscillator running and then work logically on from there.Plug your IC in and then using short lengths of PVC covered single wire, (such as that found in telephone cable,) connect negative (7) to ground and positive (14) to the positive rail. Connect the gate inputs 1 and 2, 5 and 6, 8 and 9, 11 and 12 together and to ground. Logic IC's do funny things when the gates are left floating. Do not worry about the resistor in the positive line to the IC at this stage.Because you do not have a high impedance voltmeter you will need a high impedance indicator circuit and I have attached a simple circuit which uses the 2N7000 FET. If you connect the the input to ground the LED, (any old LED will do,) will be out, connect the input to the positive line and the LED will illuminate and you can now use this circuit to monitor the outputs of the IC gates. With the gate inputs tied together and grounded the gate outputs 3, 4 10 and 11 will go high and light up your indicator if you connect to them.I have shown this in the second picture with a red LED. Note also that the battery is connnected via a 1k Ohm resistor to protect the battery in the event of inadvertant shorts. If you can get to this stage then you can slowly build the oscillator and use the indicator on pin 3 to show that oscillation is taking place but note that is is a long cycle time.Be prepared to write off the odd IC or transistor--it is part of the learning process!Kind regards.Lionel.

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  • The 31 Year LED Flasher for Model Lighthouses Etc..

    Hi Chrystyl,Sorry that you are having problems. Your eagle eye spotted the difference between the diagram and the pictures but this does not actually affect the circuit operation. The two gates accessed by pin 8-9 and 12-13 are connected in series as inverters and when one is high the other one is low. This follows through to the two 2N7000 FET's so that when one FET is switched ON the other is switched OFF and no current will flow through them except for that brief moment of switching when the point where the source of the top 2N7000 and the drain of the other will change from high or low or low to high as the circuit cycles. When this point goes high, the 4.7uF capacitor charges up via one LED giving a flash and when it goes low the capacitor discharges via the other LED giving a flash …

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    Hi Chrystyl,Sorry that you are having problems. Your eagle eye spotted the difference between the diagram and the pictures but this does not actually affect the circuit operation. The two gates accessed by pin 8-9 and 12-13 are connected in series as inverters and when one is high the other one is low. This follows through to the two 2N7000 FET's so that when one FET is switched ON the other is switched OFF and no current will flow through them except for that brief moment of switching when the point where the source of the top 2N7000 and the drain of the other will change from high or low or low to high as the circuit cycles. When this point goes high, the 4.7uF capacitor charges up via one LED giving a flash and when it goes low the capacitor discharges via the other LED giving a flash so making the two LED's flash alternately.Do make sure that the LED's are connected in parallel with one LED connected in one polarity and the other in the opposite sense. Since the parallel diodes are connected to a capacitor with it's negative to ground the LED's must be out once the capacitor is charged up or discharged. You could disconnect the diodes from the FET drain/source connection and manually connect this point momentarily to battery positive and then momentarily to ground and check that you get a flash in each state. (As a precaution you might like to put a 100 Ohm resistor in series in case of shorts.) Unless the capacitor is leaky or connected in the wrong polarity the LED's must be unlit except for the moment when you make the switch.Do check that the CMOS astable is actually working by checking that points that 8-9 and 12-13 are switching and that when one point is high the other one is low, but be aware that this circuit is extremely high impedance, (that's how the circuit is so economic,) and you will need a high input impedance voltmeter to check this without upsetting the circuit.For completeness I will add that with full night vision and darkness you will see a very slight glow from one LED or the other as the last little amount of energy enters or leaves the 4.7uF capacitor--LED's are now so very sensitive.I have reproduced this circuit some ten times either in breadboard or finished version and had no trouble and I have attached a picture of my latest oevre which is my take on the ubiquitous flower pot lighthouse which flashes away merrily with the electronics cosy inside safe from the elements.Kind regards,Lionel.

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  • A Simple Solar Charger for Nickel/Metal Hydride and Alkaline AA Cells

    Thanks for your interest Gadisha.My charger is still in regular use!

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  • A Simple Solar Charger for Nickel/Metal Hydride and Alkaline AA Cells

    Thanks for the interest Gadisha.Mine is still in regular use!

    Thanks for the interest Gadisha.Mine is still in regular use!

    Thanks for the interest Gadisha.Mine is still in regular use!

    Thanks for the interest Gadisha.Mine is still in regular use!

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  • How to Run a Battery Electric Clock on Dead Batteries

    Hi ZiP3Glad this was of interest.This is definitely one for the enthusiasts as batteries are so cheap but even so I can imagine it being useful in certain circumstances. There is the real danger of leakage as one battery dies completely before the other hence the bagging. I still get perverse amusement from squeezing the last bit of energy from spent batteries.My more recent projects have involved solar powered battery clocks and you can find these on Instructables.

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  • I missed your instructable but I have now looked at it and I envy your PCB skills and facilities.The circuit that I have shown can also be switched off in daylight by a resistor and LDR on one of the oscillator gates but I kept the circuit as simple as possible as the current consumption is so low at two microAmps.As you say the 4011, 4001 and 4004 are very handy and I think that there is still enormous potential in them even though they are so old.

    In the operation of this circuit the light does fade to an extent as the last bit of charge feeds in or out of the bucket capacitor during the respective parts of the cycle and this does seem to me to add to the realism expecially when night vision comes into play. You could add a resistor in series with the LED's which would make the flash more 'lazy'Before writing this up I did wonder if the world needs 'yet another flasher' to add to the thousands out there, however to achieve the two microAmp consumption demonstrated you would have to raise the level of complexity and probably use a programmable device such as the ATtiny85. A programmable device would also allow you to generate a fixed number of flashes if you want to emulate a known lighthouse.

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    • The 31 Year LED Flasher for Model Lighthouses Etc..
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  • Thanks for the input. That's a fair point although I have run into trouble with small clocks--we can put it down to fat fingers! A radio controlled movement can inherently be reset to 12 o'clock but most of these 'tick' and many will find them unsuitable for bedroom use.

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  • Hi GrabtharSorry about your problems. I have not encountered this with any of the super capacitors that I have purchased and indeed a little solar powered Joule Thief torch that I made for my wife holds its power for months. I would suggest just charging, discharging and recharging the items a few times as, being electrolytic devices, there may be an element of 'forming' involved.

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  • GrabtharThat's great and it shows how the combination of the supercapacitor combined with the tolerance of these clock movements to a wide range of feed voltage is so effective.I am now tempted to try to run a large outdoor clock on solar power and it might amuse the folks in our road--I believe that such clocks are rather more demanding on batteries.Thanks to you and all of the others who have shown an interest in this project.

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  • Hi GrabtharI'm delighted that it has worked for you!The box makes for a very smart job and I will keep an eye out for them for future projects.My first radio controlled clock became a bit erratic with a feed voltage above 1.7 Volts so I have kept mine below this but if it works for your clock that's fine. The 100 uF capacitor should provide plenty of reserve capacity. Here in Cornwall I know from experience that during the winter we can have 8/8 cloud and drizzle for days on end with almost zero output from the solar cell hence my use of 500 Farad automotive capacitors.Something I am playing with and that you may like to try on a breadboard is to put a silicon rectifier diode in series with, say, four or five paralleled red LED's and then place this assembly in parallel with the super cap…

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    Hi GrabtharI'm delighted that it has worked for you!The box makes for a very smart job and I will keep an eye out for them for future projects.My first radio controlled clock became a bit erratic with a feed voltage above 1.7 Volts so I have kept mine below this but if it works for your clock that's fine. The 100 uF capacitor should provide plenty of reserve capacity. Here in Cornwall I know from experience that during the winter we can have 8/8 cloud and drizzle for days on end with almost zero output from the solar cell hence my use of 500 Farad automotive capacitors.Something I am playing with and that you may like to try on a breadboard is to put a silicon rectifier diode in series with, say, four or five paralleled red LED's and then place this assembly in parallel with the super capacitor. The resulting assembly can then be connected to a solar cell which charges the capacitor up until the voltage rises to around 1.9 Volts when the excess power is dumped through the diode/LED's. This may be useful because when you charge up a capacitor from a fixed voltage the charge rate decreases as you approach charging voltage and the dumping idea I just outlined may get over this resulting in a faster charge. The LED 'Zener' characteristic is very lazy and whilst you may reach 1.9 Volt in sunlight the voltage will subside a bit to around 1.8 Volts when light is absent.Thanks for the feedback.

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  • Interesting that you mention grave lights because that is very close to what I am doing here with my two bathroom night lights which uses the circuit largely as shown in the article with a couple of later embellishments that improve the efficiency. Also it switches off in daylight which I would imagine is important for a grave light. I can set the power consumption for useable light output at around 2 mA at which level a 'dead' battery can last for months and an alkaline 'D' cell should give years and years. Give me a day or two and I will post the circuit here.

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  • Thanks for that and great to hear that my Instructable is useful and reproducible. All the best for your future efforts.

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  • I am puzzled. Once the voltage at the wiper of the potentiometer goes over around 0.5 Volt then Q2 should start to conduct and thus start to turn off the oscillator which then usually goes into a mode where you have short bursts of oscillation. If you set a light output at a lowish but useful light output the circuit should maintain this over the battery life. With your example above you should be able to set the circuit at 1.55 mA/0.8V and then hold this for various battery voltages up to the maximum. You cannot make the basic circuit give more than it does at at 0.8V.

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  • Thanks for your interest and I'm sorry that you are having problems. One thing that may be a problem is that the Instructables software has clipped the left hand side of the schematic and thus vital connections are not shown. I will see if I can correct this by putting a border around the schematic. The picture of the breadboard shows correctly.It may help if you get a basic Joule Thief circuit working at its very simplest with a toroid as shown in the accompanying pictures. You can then substitute your transformer and see if that still oscillates. I think that you do need a toroid of some pedigree and the one shown is made from Ferroxcube. (see Ebay or Amazon)I think that it it is very helpful to measure circuit efficiency and I can show you how to do this if you would like.

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  • Thanks for that GregW171, It's really great when someone picks up one of your ideas and makes a success of it.

    Some further thoughts. . .The battery electric clock consumes power in 30 mS pulses every second and virtually zero for the rest of the cycle and this makes an average power consumption extremely difficult to measure.The picture shows my attempt at this. A wooden dowel with a small piece of printed circuit board stuck to each end is inserted into the clock in place of the battery and it allows the clock power connections to be brought out and plugged into a solderless breadboard. Connected to the breadboard you can see a battery which feeds a 10 Ohm resistor in parallel with a 3 Farad super capacitor in series with the clock. To measure the clock current connect up and measure the voltage across the 10 Ohm resistor--it may take a little time for the system to equilibrate. You will need …

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    Some further thoughts. . .The battery electric clock consumes power in 30 mS pulses every second and virtually zero for the rest of the cycle and this makes an average power consumption extremely difficult to measure.The picture shows my attempt at this. A wooden dowel with a small piece of printed circuit board stuck to each end is inserted into the clock in place of the battery and it allows the clock power connections to be brought out and plugged into a solderless breadboard. Connected to the breadboard you can see a battery which feeds a 10 Ohm resistor in parallel with a 3 Farad super capacitor in series with the clock. To measure the clock current connect up and measure the voltage across the 10 Ohm resistor--it may take a little time for the system to equilibrate. You will need a voltmeter able to measure in the milli-Volt range. The use of a super capacitor might seem extreme but normal large electrolytics could not begin to touch it.I tried the circuit on four house clocks. I started with a cheap one mounted on a flattened beer bottle and equipped with a second hand and this yields 4 milli-Volts denoting a current of 400 micro-Amps. The three remaining clocks had no second hands fitted, were of better quality and these yielded current consumptions int the 270 to 390 micro-Amp range.Thus I found some but not a massive improvement when no second hand was on the clock but the experimenter would be advised to make his/her own measurements especially if dealing with larger clocks with bigger hands.This crude experiment does give an indication of the power you are going to have to find to run a clock 24/7/365.

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    • How to Switch Off a Joule Thief During Daylight
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    • How to Run a Battery Clock on Solar Power
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  • Thanks for the query!You may be making things unnecessarily complicated and in view of the fortunate latitude of your location I think that there may be a very easy solution. A 2 volt solar cell placed in your kitchen window could charge a super capacitor up to around 1.4 Volts using the circuit shown. (They don't come much simpler than this one!)The solar cell can be a salvaged item from a garden light and you could use two in parallel. The diode is necessary to prevent the power from leaking back through the solar cell but there is a cost due to the forward voltage drop of the diode. By replacing the Schottky diode with a germanium one you could gain another very useful 0.2 Volts or so.This circuit works well in the summer at my latitude but runs out of steam around October. With your l…

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    Thanks for the query!You may be making things unnecessarily complicated and in view of the fortunate latitude of your location I think that there may be a very easy solution. A 2 volt solar cell placed in your kitchen window could charge a super capacitor up to around 1.4 Volts using the circuit shown. (They don't come much simpler than this one!)The solar cell can be a salvaged item from a garden light and you could use two in parallel. The diode is necessary to prevent the power from leaking back through the solar cell but there is a cost due to the forward voltage drop of the diode. By replacing the Schottky diode with a germanium one you could gain another very useful 0.2 Volts or so.This circuit works well in the summer at my latitude but runs out of steam around October. With your location you stand a much better chance especially if your kitchen window gets some direct sunlight on a regular basis.Note that the super capacitor is an automotive one of 500 Farad capacity.Note also that this simple circuit charges quickly when the capacitor is 'empty' but the charge rate slows down as you head towards the upper voltage limit.

    I have hacked single solar lights for parts and to modify but not a string. It seems to me that the circuitry is similar with the solar panel charging a 1.2V Ni/MH rechargeable cell which then powers the LED or LED string via a step up circuit. Voltage from the solar cell turns off the circuit during daylight. Two possibilities come to mind:1. Disconnect a string from the solar unit and try it on a well tempered Joule Thief. If the LED's are bright enough then simply run each string from its own Joule Thief and power them all from the super capacitor.2. Take out the Ni/MH cell from a unit and feed power in to this point from an external source. Although the step up circuit normally runs on a steady 1.2 Volts it would be interesting to know if the circuit will run, say, from 1.5 Volts do…

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    I have hacked single solar lights for parts and to modify but not a string. It seems to me that the circuitry is similar with the solar panel charging a 1.2V Ni/MH rechargeable cell which then powers the LED or LED string via a step up circuit. Voltage from the solar cell turns off the circuit during daylight. Two possibilities come to mind:1. Disconnect a string from the solar unit and try it on a well tempered Joule Thief. If the LED's are bright enough then simply run each string from its own Joule Thief and power them all from the super capacitor.2. Take out the Ni/MH cell from a unit and feed power in to this point from an external source. Although the step up circuit normally runs on a steady 1.2 Volts it would be interesting to know if the circuit will run, say, from 1.5 Volts down to 0.8 Volts. If it does then feed in power from your super capacitor to a number of units in parallel.Regarding option 1 the simple Joule Thief does not have the facility for switching off during daylight but I have found a very cheap and simple way to do it and this is to be the subject of my next Instructable.Thanks for possibly stimulating some ideas!

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  • Thanks for your interest (and to everyone else who has commented.)Yes and a good point although I do rather like to see the second hand going round--it shows that the clock is still going :-) In the case of a radio controlled clock I would see it as important to have the second hand since a selling point of the device is that it really is accurate to the second.Interesting though and I will do some measurements as it could help bring the ability to run a solar powered clock into the dimmer regions of the the modern house.

    That's a good idea. Taking into account the inherent drop of 0.6 Volt in the regulator then the supercapacitor would give useful power as it drops from 2.5 to 1.6 Volt whereas with what I have done we use the power of the super capacitor from 1.5 down to just over a Volt. This at the price of a slight extra complication.From my previous work I know that what I have done works at my latitude all the year round with a super capacitor of 50 farad so 500 should enable it to work much farther north. Your idea could take it even farther north.

    This is true but it does take you out of the realm of what you already have in the junk box or can get through simple eBay suppliers and up to professional suppliers like, (in the UK,) RS and Farnell with associated minimum order sizes. There must surely be a vast potential in super capacitors and efficient ways of using them as in what you suggest will be very important.

    One great thing about capacitors is that you can put them in parallel by the boxful if you want!I suspect that the best approach will be to put two 500 Farad super capacitors in series to produce a 5.5 Volt 250 Farad unit and then put numbers of these units in parallel.There are cheap efficient step up voltage converters that would enable you to extract the powerefficiently as the capacitor voltage drops from 5 to 2 Volts.You can place the solar cell in a remote position and the lead length could be large since the current levels are relatively modest.I have had some success just simply propping the cell up against a favourable window pane inside the house.

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  • Hello samtani2013 - Apologies for my late reply but I have had problems recently logging on to Instructables.1. You can never produce more output power than that supplied by the batteries--we must live our lives by basic physical laws :-) I think that the spiky waveform produced by this circuit makes current measurement extremely difficult and this is where false hopes are generated. Proper measurement of the efficiency of a Joule Thief circuit is therefore vital for serious experimentation and this is the way that I do it.Make sure that the power input is well decoupled using a high value electrolytic capacitor e.g. 1000 microfarad connected between the supply rail and ground. This will ensure that the supply current and voltage can be properly measured and then the power into the circ…

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    Hello samtani2013 - Apologies for my late reply but I have had problems recently logging on to Instructables.1. You can never produce more output power than that supplied by the batteries--we must live our lives by basic physical laws :-) I think that the spiky waveform produced by this circuit makes current measurement extremely difficult and this is where false hopes are generated. Proper measurement of the efficiency of a Joule Thief circuit is therefore vital for serious experimentation and this is the way that I do it.Make sure that the power input is well decoupled using a high value electrolytic capacitor e.g. 1000 microfarad connected between the supply rail and ground. This will ensure that the supply current and voltage can be properly measured and then the power into the circuit is given by:Supply voltage multiplied by supply current (V * I)To calculate the output power I place a 10 microfarad electrolytic capacitor in parallel with a 10 Ohm resistor between the LED and ground and then measure the voltage developed across the resistor/capacitor combination. You will need a quality digital voltmeter to do this as a 1 milliamp LED current will generate only 10 millivolts across 10 Ohms. Hence you will see that the output LED current is given by :Voltage across the 10 Ohm resistor multipled by 10 (the value of the resistor)To calculate the output power in the case of this 1 milliamp: we know that the voltage across a working white LED is 2.5 Volts, (you may like to measure it accurately and separately with a power supply and resistor in series,) and then the LED power is 2.5 X 0.001 = 2.5 milliWatt.The circuit efficiency is given by (LED power / power in) times 100.In practice I am finding that a well tempered Joule Thief can have an efficiency of 50 to 70% with a supply battery voltage of over 1 Volt but this efficiency drops away as the supply voltage drops down even though the circuit is still producing light.2. Mains transformers can be used to make transistor inverters but they are not designed for this duty and the efficiency will not be very high especially with a small transformer.

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  • Thanks for your interest.The key here is how long does it glow and will it glow all night?I think that the products based on zinc sulphide without radioisotope activation will not and I think many products fall into this category. They are very impressive to start with especially if you expose them to a bright light but fail to deliver after an hour or so.Read the reviews from those who have purchased the luminous alarm clocks that are widely and cheaply available and you will detect an underlying theme of disappointment with the luminosity.The green variety of rare earth doped strontium aluminate really does glow all night after activation and perhaps it is the coarse nature of the product that stops its wider application--fundamentally it is not based on expensive materials.Regarding y…

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    Thanks for your interest.The key here is how long does it glow and will it glow all night?I think that the products based on zinc sulphide without radioisotope activation will not and I think many products fall into this category. They are very impressive to start with especially if you expose them to a bright light but fail to deliver after an hour or so.Read the reviews from those who have purchased the luminous alarm clocks that are widely and cheaply available and you will detect an underlying theme of disappointment with the luminosity.The green variety of rare earth doped strontium aluminate really does glow all night after activation and perhaps it is the coarse nature of the product that stops its wider application--fundamentally it is not based on expensive materials.Regarding your point regarding duct tape I see that clear duct tape is available although I have never used it. As a suggestion it might be an idea to lay some out on a surface from which it can be peeled and then carefully spread some 'glow in the dark' powder in the central area. Then place another tape layer on top sealing your powder in. You can now peel off your combined product sandwich and deploy elsewhere.

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    • How to Give a Wall Clock Luminous Hands and Time Interval Markers
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  • Thanks for your interest. I don't think that there will be problems in the latitude of South Florida--plenty of sun!The radio controlled clock here is still where it was placed in March 2016 and has run faultlessly ever since. Importantly, it has coped with the 'spring forward/fall back' adjustment where the clock has to have the power to wind back eleven hours in October. The clock can stay there now and it should carry on running so long as there is a long wave radio signal and daylight!Even now, there may be ways of deploying the solar cells in a more efficient way and thus cope with poor light levels or maybe take advantage of artificial light. If I come up with anything I will tag it on to this article.

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    • How to Make Glow in the Dark Adhesive Stickers and Magnets
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  • Hi Skistler and thanks for the interest.The powder that I purchased came in 10 gram bags and, since I had one unopened, I scattered the contents over a 4 inch square of black card and I have attached a picture. From this I would suggest that 20 grams would do the job.That said, I think that scaling up will present challenges. I have been very generous with the applications shown in the article and the resulting surface has tended to be a little uneven physically although this does not degrade the visual effect.For large areas I would imagine that the even application of the nail varnish will be important and maybe thinning with pure acetone may help. Also applying the powder from a height from a vessel such as a free running salt cellar might be a good thing.Do bear in mind that nail var…

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    Hi Skistler and thanks for the interest.The powder that I purchased came in 10 gram bags and, since I had one unopened, I scattered the contents over a 4 inch square of black card and I have attached a picture. From this I would suggest that 20 grams would do the job.That said, I think that scaling up will present challenges. I have been very generous with the applications shown in the article and the resulting surface has tended to be a little uneven physically although this does not degrade the visual effect.For large areas I would imagine that the even application of the nail varnish will be important and maybe thinning with pure acetone may help. Also applying the powder from a height from a vessel such as a free running salt cellar might be a good thing.Do bear in mind that nail varnish and acetone are highly inflammable and as you scale up in size the vapours become quite narcotic so good ventilation is vital.I hope you are successful.

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    • How to Add ' Glow in the Dark' LED Eyes to a Plaster of Paris Ornament
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    • Adding an LED Back Light to an ACCTIM BENTIMA  LCD Alarm Clock
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  • Thanks for your interest.We have had the same experience with garish green alarm clock displays and had to resort to coloured films and cloths but it was never right and the offending clock went to the charity shop in the end. We got a red one which was much better being in a visible region that is kinder to the eyes but all of them need a facility whereby you can turn the display intensity right down to almost zero. With the LED battery being external in this case it might, in principle, be possible to turn off the LED during daylight. Semiconductor photocells work in the wrong sense in that they are high resistance in the dark so you would have use one to turn off a series transistor but it might be tricky to control the starvation current of a few micro-amps that we are using. The …

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    Thanks for your interest.We have had the same experience with garish green alarm clock displays and had to resort to coloured films and cloths but it was never right and the offending clock went to the charity shop in the end. We got a red one which was much better being in a visible region that is kinder to the eyes but all of them need a facility whereby you can turn the display intensity right down to almost zero. With the LED battery being external in this case it might, in principle, be possible to turn off the LED during daylight. Semiconductor photocells work in the wrong sense in that they are high resistance in the dark so you would have use one to turn off a series transistor but it might be tricky to control the starvation current of a few micro-amps that we are using. The hope is that our battery will last a very long time.

    One side of our aforementioned partnership agrees with you! I, in the other hand will own up to 'dubious dongle' :-)My plan B is indeed to go the Joule Thief route with the circuit powered by the clock's own battery. This would allow a completely sealed solution with no further access to the interior required. But. . . there are things to consider. Space is tight! I think it reasonable to allow a budget of 0.2 mA continuous power consumption for the Joule Thief so as not to cause frequent battery changes; this is quite a big ask but possible. The circuit needs to be stable, you do not want to be adjusting the circuit or even having to have a hole in the casing to access a trimming pot. Watch this space.

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  • Thank you for your interest and sorry for the delay in my reply.I have an ongoing interest in applying the Joule Thief circuit and I have built a number of them over the last year or so. My feeling is the the single most important factor in the construction of the transformer is the use of bifilar winding i.e. the wires must be tightly twisted together before winding on to the toroid. If you are adding a third winding for some reason the use trifilar. I general I think it is a good idea to keep the number of windings up to bring the oscillator frequency down to reduce capacitive losses and maybe even radio frequency interference.It is tempting to do the winding in two stages bringing the centre tap out for connection to the positive rail but my experience is that this can cause difficu…

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    Thank you for your interest and sorry for the delay in my reply.I have an ongoing interest in applying the Joule Thief circuit and I have built a number of them over the last year or so. My feeling is the the single most important factor in the construction of the transformer is the use of bifilar winding i.e. the wires must be tightly twisted together before winding on to the toroid. If you are adding a third winding for some reason the use trifilar. I general I think it is a good idea to keep the number of windings up to bring the oscillator frequency down to reduce capacitive losses and maybe even radio frequency interference.It is tempting to do the winding in two stages bringing the centre tap out for connection to the positive rail but my experience is that this can cause difficulties in the starting of the circuit even if the windings are very close on the toroid. (A Joule Thief that does not start reliably is a disaster as there is a near short circuit from the positive rail through the transformer to the transistor collector and then from the transistor emitter to ground.)Considering the use of different turns ratios for the transformer I cannot comment as I have always successfully used 1:1 but I will have a go on the breadboard at varying the ratio to see if there is any improvement in efficiency to be had--the LED does present a very strange load to the circuit.

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  • Thanks for your interest Mark.The critical factor is that each cell has its own diode and resistor in series. The diode isolates each cell from the others and the resistor drops the voltage and limits the current to that cell. Hence although you may have six volts applies to the diode and resistor the voltage across the cell itself will only be up to 1.4 Volts with the voltage difference being dissipated in the resistor. If you insert a totally flat Ni/MH cell and monitor the voltage across it as it charges over time you will see it come up fairly rapidly to around 1.2 Volts where it will stay while the battery absorbs charge and then, when the battery is charged, the voltage will rise to 1.3 to 1.4 Volts. At this point the battery is 'float charging' and the energy is converted into…

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    Thanks for your interest Mark.The critical factor is that each cell has its own diode and resistor in series. The diode isolates each cell from the others and the resistor drops the voltage and limits the current to that cell. Hence although you may have six volts applies to the diode and resistor the voltage across the cell itself will only be up to 1.4 Volts with the voltage difference being dissipated in the resistor. If you insert a totally flat Ni/MH cell and monitor the voltage across it as it charges over time you will see it come up fairly rapidly to around 1.2 Volts where it will stay while the battery absorbs charge and then, when the battery is charged, the voltage will rise to 1.3 to 1.4 Volts. At this point the battery is 'float charging' and the energy is converted into oxygen and hydrogen gas by electrolysis and then the gases recombine to form water.The resistor limits the charge current to just a few mA so the charging is slow and the charging and float charging is at a very gentle small current. When time is not too important this doesn't matter. Note that I gave a wide range for the series resistors--with low value resistors you will get a faster charge especially in good quality sunlight but then the subsequent float charging will be higher and you may be happier taking the cells off charge when full . With higher value resistors the charging will be slower but the float charging will be less aggressive and you can leave the cells in the device ready for use in tiptop condition.Note that your 6V 150 mA solar panel will only give this power in full sunlight. In dull conditions this will drop drastically but our charger will continue to put at least a little something into each of the cells.This overall concept may seem a bit wasteful but we do get the energy for free!

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  • Hello and thanks for the interest.Yes indeed. The method of control relies on the output being rectified to produce a positive voltage which is fed back to the transistor which is connected to the oscillator transistor base turning it on and turning down the oscillation. So to answer your question, the positive voltage can also come from an external source and a 2 Volt solar cell salvaged from a defunct garden light is perfect this being shown in the final stages of the article.The Joule Thief is perfect for a newbie. It will work on a solderless breadboard and you can learn much putting one together and it actually does something i.e. lights up. Be prepared to write off the odd LED or transistor but that is all part of the fun!

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  • Thanks enormously for that and I will now do some editing. On the first point I will add the LED in to the schematics.Regarding the second point I admit to being a little unclear. The circuit is correct but the solar cell is being used as a very cheap (scavenged) component to control a circuit rather than be a source of solar power. Inside a house there is very little energy left in the daylight once it gets through the windows and not enough in general to yield very much from a solar cell--you might source some energy by positioning the cell on a window sill, up against a window or perhaps catching a transient shaft of sunlight. However there is more than enough to provide the few microwatts of power required to switch off the Joule Thief when not required in daylight and thus preven…

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    Thanks enormously for that and I will now do some editing. On the first point I will add the LED in to the schematics.Regarding the second point I admit to being a little unclear. The circuit is correct but the solar cell is being used as a very cheap (scavenged) component to control a circuit rather than be a source of solar power. Inside a house there is very little energy left in the daylight once it gets through the windows and not enough in general to yield very much from a solar cell--you might source some energy by positioning the cell on a window sill, up against a window or perhaps catching a transient shaft of sunlight. However there is more than enough to provide the few microwatts of power required to switch off the Joule Thief when not required in daylight and thus prevent waste of battery power. I will go back and emphasise this point in the text.This does raise the interesting point regarding the possibility of a solar powered night light. I think that it is a viable project but such a device must work 24/7, winter/summer and ideally in as many parts of the world as possible and it certainly is not as simple as it sounds. It will need more effort than modifying a solar garden light!Thank you again for your help.

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  • Thanks for your interest.The diodes isolate each individual cell from all of the others. This is necessary otherwise cells with more charge would discharge into other cells possessing lower charge especially when the solar cell is not illuminated. This will happen for instance when you have three cells fully charged or well on their way to being charged and you put on one flat cell. Conventional wisdom is that it is not a good idea to charge nickel cells in parallel as their individual characteristics vary and they cannot be relied upon to properly share the current.

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