The 31 Year LED Flasher for Model Lighthouses Etc..

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Introduction: The 31 Year LED Flasher for Model Lighthouses Etc..

About: 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 day...

Model lighthouses hold a wide fascination and many owners must think how nice it would be if, instead of just sitting there, the model actually flashed. The problem is that lighthouse models are likely to be small with little room for batteries and circuitry and the tea-light shown in the picture above is a good example where there is just room to squeeze in a PP3 battery or a small stack of lithium button cells along with a very small circuit board.

The internet abounds with LED flashers. Many are based on the 555 chip and hence can be expected to consume around 10 mA of current which would flatten a small battery within days. After some desultory playing with components on a breadboard I stumbled upon the CMOS circuit that is the basis for this article. This circuit is 5000 times better than a 555 and consumes 2 microAmps which means that an alkaline 9 Volt PP3 battery should last 31 years although this is academic as it is well beyond the shelf life of the battery. A stack of 3 X 2032 lithium cells also giving 9 Volts will last a mere 12 years.

To achieve this performance some rules are broken and electronics professionals will raise an eyebrow if not two.

Step 1: The Basic Circuit 1

It may be helpful to get the circuit going initially on a solderless breadboard and besides the breadboard you will need:

1 X CMOS CD4011 quad NOR gate. (We are using the IC as a quad inverter so a CD 4001 will also work.)

1 X 4.7 Meg Ohm resistor. (Up to 10 megOhm can be used for longer cycle times.)

1 X 10 Ohm resistor.

1 X 1000 microFarad electrolytic capacitor.

1 X 1 microFarad non polar electrolytic capacitor. (1 microFarad ceramic capacitors may be used but they are a little harder to source.)

2 X high efficiency white LED's.

2 X 2N7000 N channel FET.

1 X 4.7 microFarad electrolytic capacitor (tantalum would be best.)

1 X 9 Volt battery such as a PP3.

The schematic above shows the basic circuit. A CMOS CD 4011 has all pairs of gate inputs tied together making it a quad inverter. Two of the gates are wired as an astable with the timing defined by the 4.7 megOhm resistor and the 1 microFarad non-polar electrolytic capacitor resulting in a cycle time of three to four seconds. The time can be easily doubled by the addition of another 1 microFarad capacitor or more in parallel and the 4.7 megOhm resistor can be increased to 10 megOhm so long cycle times are feasible. The remaining two gates are wired as inverters fed from the astable section and their antiphase outputs feed the respective gates of the 2N7000 FET's which are wired in series across the supply line. When the last inverter in the chain output goes high the one before will be low and the top 2N7000 conducts charging up the 4.7 microFarad capacitor via one LED giving a flash. When the last inverter in the chain goes low then the bottom 2N7000 conducts allowing the 4.7 microFarad to discharge through the other LED giving another flash. The output stage consumes zero current outside of the transition times.

The 10 Ohm resistor and the 1000 microfarad capacitor in the power supply line are just for decoupling and are not vital but are very useful in the testing stage.

Electronic purists will point out the the output stage is not good design because any dithering or uncertainty at the point where the circuit switches could result in both 2N7000's being switched on briefly at the same time resulting in a short across the power supply. In practice I find that this is not happening and would show up in the current consumption, see later.

The circuit as shown was found to consume an average of 270 microAmps which is creditable but far too high for our purpose.

Step 2: The Basic Circuit 2

The picture above shows the circuit assembled on a solderless breadboard.

Step 3: The Enhanced Circuit 1

The circuit shown in the schematic above looks to be almost identical to the previous one. Here the addition of just one component effects a transformation in performance that is as drastic as you are ever likely to see in simple electronic circuitry.

A 1 MegOhm resistor has been placed in series with the supply to the CD4011 IC. (Electronics professionals will say that this is something that should never ever be done.) The circuit continues to operate BUT the average consumption drops to some 2 microAmps which equates to a life of 31 years for an alkaline PP3 cell of 550 mA hours capacity. Incredibly, the output voltage is still high enough to reliably switch the 2N7000 FET's.

Step 4:

The picture above shows the added resistor ringed in red.

Measuring the average current drawn by this circuit is a daunting task but a quick test is to remove the battery and allow the circuit to run down on the charge in the 1000 microFarad decoupling capacitor if you have fitted it--the circuit should run for five or six minutes before one of the flashes gives up.

I have had some success by inserting a 100 Ohm resistor plus 3 Farad super capacitor, (observe polarity,) in parallel into the supply line and allowing several hours for equilibrium to be reached. Using a milli-Voltmeter the voltage across the resistor can be measured and the average current calculated using Ohm's Law.

Step 5: Some Thoughts at This Stage.

I have committed the cardinal sin of placing a resistor in the supply line of a CMOS IC. However the IC is standing alone and not part of a logic chain and I would suggest that we are using this single IC simply as a collection of complemetary CMOS transistors. It may be that we have here a poor man's ultra low power relaxation oscillator.

The 'bucket' capacitor that charges and discharges through the two LED's can be increased to provide a brighter flash but with values in the hundreds of microFarads it may be a wise precaution to add a small resistor in series with the LED's to limit peak current and 47 or 100 Ohms is suggested. With larger capacitor values the flash may get a little 'lazy' as the last part of the capacitor charge dissipates through the bottom LED although you may consider that it provides a more realistic lighthouse experience. The current consumption will rise of course maybe even to twenty or thirty microAmps.

Step 6: Making a Permanent Version of Your Circuit 1.

We have done the easy part but should have proved that the circuit works and can now be committed to a permanent form to go into our lighthouse.

This will require elementary electronic tools and assembly skills. The components needed will depend on how you choose to do this part and the skills that you have. I will show a couple of examples and give further suggestions.

The picture above shows a small double-sided Prototype PCB stripboard point to point circuit board. These are available on EBay in a number of sizes and this one is one of the smallest. Also shown is a square of plain printed circuit board with a wire attached and this will form one connection for our battery which is to be a stack of three lithium button cells. With this type of board I find that it is not possible to bridge adjacent pads with solder as the solder runs down through the holes--you must bridge with wire.

Step 7: Making a Permanent Version of Your Circuit 2.

In the picture above we see that construction is well under way. Note that two 1 microFarad capacitors were used for timing and three 2025 lithium button cells are ready to be sandwiched between the battery end connectors.

Step 8: Making a Permanent Version of Your Circuit 3.

In the picture above we see the finished article ready to be installed in a lighthouse. Note that the three lithium cells have been connected in series positive to negative up to the top positive which is connected to the square of plain PC board soldered to the red lead. The stack of cells has then been bound together tightly with self-amalgamating tape. You will find examples of this method of making batteries from multiple button cells elsewhere on the Instructables site.

Step 9: Making a Permanent Version of Your Circuit 4.

In the picture above we see another version assembled on stripboard which is the modern version of Veroboard. This is fine but modern board is unforgiving of mistakes and will not stand much soldering and desoldering before the copper strips lift, so do get it right the first time! The battery is an alkaline PP3 which at 450 mA hours capacity calculates to a rather academic 31 years life.

Step 10: Making a Permanent Version of Your Circuit 5.

Here the stripboard circuit plus PP3 battery have been cocooned in plastic packing material and wedged into the tealight holder which allows our assembly to be inserted up into the lighthouse.

For a simple circuit like this you can also make your own printed circuit board with a printed circuit pen but you have to be able to etch it, preferably not in the kitchen! Lastly a small sheet of plain printed circuit board can be the subject of 'dead bug' construction which can give the smallest and most robust construction of all of the examples.

Step 11: Last Thoughts.

This circuit is so cheap to make as to be disposable . It can be made so small as to go into a small glass jar and then even potted in resin or wax if the LED's are left in the clear. In such a robust form there may be a multitude of potential uses. I would suggest that it could be a valuable safety item in caving and especially cave diving where a number of these could illuminate a way out of a cave or from the inside of a tortuous wreck. They could be left in place for years.

The bucket capacitor may be made smaller lowering the power consumption to a level where the circuit could be driven by a 'pile' battery of dissimilar metal plates interleaved with electrolyte pads. This might even result in an assembly that could be placed in a 'time capsule' to be dug up some fifty years later!

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    14 Discussions

    0
    maximzodal
    maximzodal

    1 year ago

    Interesting circuit. It appears to be just a flasher. Is there a way to have the LED fade so as to better look like a lighthouse light?

    0
    pianomatt
    pianomatt

    Reply 11 days ago

    I don't know if this will work with this circuit, but when I want a "breathing" LED I use an astable multivibrator with a second stage that adds an RC timer and a transistor amplifier.

    breathing_led_circuit_diagram.png
    0
    Lionel Sear
    Lionel Sear

    Reply 9 days ago

    Hello Matt
    It 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.

    0
    Lionel Sear
    Lionel Sear

    Reply 1 year ago

    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.

    0
    ChristyI
    ChristyI

    8 months ago

    Hello, thank you for posting your circuit.
    I would like to ask a couple of questions. Should the 2 LEDs alternately flash or both flash together? I built the circuit but unfortunately I don't get any flashes, the LEDs stay lit. I tried to follow your schematic exactly but I obviously made a mistake. It does appear that the pictures differ slightly from the schematic. In the diagram it looks like pin 3 is connected to pin 8-9 but in the picture it looks like pin 3 is connected to 12-13. Did you run into the "no flash" problem when you were experimenting with the circuit? -Thanks

    0
    Lionel Sear
    Lionel Sear

    Reply 8 months ago

    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.



    Flower Pot Lighthouse.jpg
    0
    ChristyI
    ChristyI

    Reply 8 months ago

    Thank you Mr. Sear for the detailed explanation, I appreciate the effort to help a wayward tinkerer. My LEDs are properly oriented and I believe the FETs are also wired correctly, I will try the direct connect to + and - to see if they alternate, that was a good suggestion, wish I would have thought of it..
    I have to think that my 2N7000 is not in astable mode and I don't have a high input impedance voltmeter so I will just keep trying things. One more rudimentary question if I may, when connecting to a pair of joined pins does it ever matter which pin you use? I wouldn't think so but I am to the point of checking all my assumptions.

    Nice set of flower pots, I especially like the lantern room. Thank you, John

    0
    Lionel Sear
    Lionel Sear

    Reply 8 months ago

    Hi John
    I 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.

    LED Indicator.jpgIndicator Circuit.jpg
    0
    ChristyI
    ChristyI

    Reply 8 months ago

    Excellent suggestions and thank you for the diagram, pictures help me a lot. I finally got it working. My problem seemed to be with the 1uF non polar capacitor (or more accurately, my 200nF capacitor). My little bag of 105 capacitors turned out to actually be 104 value. I didn't have any higher values so it took me a while to try combining them to get a higher capacitance. Thank you again for all your efforts.

    If you don't have any objections, I hope to eventually put your design into a circuit board to make future projects much easier and reliable. I can send you the Gerber files if you are interested. I can usually get about 5-10 un-populated boards for around $10 from China.

    0
    Lionel Sear
    Lionel Sear

    Reply 8 months ago

    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.


    0
    Mic100
    Mic100

    1 year ago

    The 4011, 4001 and 4004 are very handy for many electronic projects, I also illuminated my headlight with a CD4004 for the command day & night by a LDR cell and Flash with a NE555

    here is my instructable: https://www.instructables.com/id/Pimp-Your-Mini-Li...

    0
    Lionel Sear
    Lionel Sear

    Reply 1 year ago

    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.

    0
    Mic100
    Mic100

    Reply 1 year ago

    Hi Lionel
    It's true that editing with LDR and NE555 increases the consumption a lot but I use rechargeable NiMh batteries.
    For PCBs, I use Kicad a free software that allows to make the schematic, the PCB, the 3D view, those who do not want to burn their PCB, Kicad creates the files Gerbert allowing to have it manufactured, it can also create simulation files for LTspice.
    If you want to get started, there's a lot of tutorials on the Web.
    Here is the link Kicad: http://kicad-pcb.org/

    0
    WeTeachThemSTEM
    WeTeachThemSTEM

    1 year ago

    Thanks for sharing your process and the additional circuit versions! The extensions you mention in step 11 are pretty brilliant too. :)