dr_phil

Hi again. The core of this system is based on a resistive bridge circuit and firmware developed by Beric Dunn. The calculation is taken directly from his code. If you look at Wikipedia, under VSWR, you'll see that:VSWR = |Vmax| / |Vmin| = (|Vf|+|Vr|) / (|Vf|-|Vr|)The Arduino sketch uses the second part of this formula. I think Beric's resistive bridge uses diodes and low pass filters to obtain the modulus (magnitude) of the forward and reverse voltages (FWD and REV respectively), then calculates:VSWR = (FWD+REV) / (FWD-REV).I'd need to check this on LTSPICE to satisfy myself 100%, but I think this is what is happening in the circuit. The Dunn circuit and code is very widely used by amateurs.Wikipedia also reports that for a purely resistive load,VSWR = (Rload/Zline) ^ (+/- 1),with the s...

Hi again. The core of this system is based on a resistive bridge circuit and firmware developed by Beric Dunn. The calculation is taken directly from his code. If you look at Wikipedia, under VSWR, you'll see that:VSWR = |Vmax| / |Vmin| = (|Vf|+|Vr|) / (|Vf|-|Vr|)The Arduino sketch uses the second part of this formula. I think Beric's resistive bridge uses diodes and low pass filters to obtain the modulus (magnitude) of the forward and reverse voltages (FWD and REV respectively), then calculates:VSWR = (FWD+REV) / (FWD-REV).I'd need to check this on LTSPICE to satisfy myself 100%, but I think this is what is happening in the circuit. The Dunn circuit and code is very widely used by amateurs.Wikipedia also reports that for a purely resistive load,VSWR = (Rload/Zline) ^ (+/- 1),with the sign of the exponent selected such that VSWR>1. So a 200 ohm resistor presented to the analyser should show a reading of (200/50) ^ (+1) = 4. A 12.5 ohm resistor should give the same answer (using an exponent of -1).If you have access to a commercial antenna analyser it would be very interesting to carry out a comparison with a real antenna and report back. I don't, so I have to rely on fixed resistors. I know that my rig's ATU won't work above about 3:1 SWR, and this is consistent with the results shown on my analyser.I hope this helps :-)

Thanks - it seems still to be generating a lot of interest. I think you could use the clock generator you suggest, but you may wish to add some sort of filter as the output will be closer to a square wave and thus will be rich in harmonics. The AD9850 just does the job 'out of the box' and doesn't cost that much. It will take me a while to check your schematic, particularly as I don't know much about the Si5351. Thanks for sharing it though.The AD9850 module is controlled via four pins in the current design: FQ_UD, SCLK, SDAT and RESET. The module uses SPI comms. The subroutines SetDDSFreq and send_byte send the frequency information to the module. I can't help you with the specifics of your clock generator I'm afraid - I know nothing about it. Unless money is very tight, I would recomm...

Thanks - it seems still to be generating a lot of interest. I think you could use the clock generator you suggest, but you may wish to add some sort of filter as the output will be closer to a square wave and thus will be rich in harmonics. The AD9850 just does the job 'out of the box' and doesn't cost that much. It will take me a while to check your schematic, particularly as I don't know much about the Si5351. Thanks for sharing it though.The AD9850 module is controlled via four pins in the current design: FQ_UD, SCLK, SDAT and RESET. The module uses SPI comms. The subroutines SetDDSFreq and send_byte send the frequency information to the module. I can't help you with the specifics of your clock generator I'm afraid - I know nothing about it. Unless money is very tight, I would recommend using the AD9850 which does exactly what you need - what's your time worth?Good luck...

Ah - that makes sense. I'm happy to help with debugging the SWR calc, but I'm sure you've got it covered. I still don't understand the graph data storage though. Because your code will just sweep the frequency until you tell it to stop, the code doesn't know in advance how often to sample the SWR reading to generate the graph array. Or am I misunderstanding?Cheers

Hi bi3qwq. I had some problems getting your sketch to fit on my Nano (max 30720 bytes). I had to go through it trimming out lots of text etc. before I could get it to fit. Now it's installed, I can have a proper play.* The display looks great, although the bar graph and figures overflow when the antenna port is open circuit.* The encoder button and DDS module use different pins on my hardware, but this was easily changed in your sketch.* I think there is definitely a problem with the calibration routine, as your screen (for example) reads an SWR of about 7 for a measured resistance of about 150 ohms. The actual value should be around 3.I think if you can revisit the SWR calculation and calibration aspect, and perhaps investigate why it doesn't fit on some Nanos (this could be a problem ...

Hi bi3qwq. I had some problems getting your sketch to fit on my Nano (max 30720 bytes). I had to go through it trimming out lots of text etc. before I could get it to fit. Now it's installed, I can have a proper play.* The display looks great, although the bar graph and figures overflow when the antenna port is open circuit.* The encoder button and DDS module use different pins on my hardware, but this was easily changed in your sketch.* I think there is definitely a problem with the calibration routine, as your screen (for example) reads an SWR of about 7 for a measured resistance of about 150 ohms. The actual value should be around 3.I think if you can revisit the SWR calculation and calibration aspect, and perhaps investigate why it doesn't fit on some Nanos (this could be a problem with my set-up, admittedly), then it all looks really good. The bar display and the graph zooming feature are cool, and it's much easier to pick an operating frequency than on mine. Nice work...Cheersdr_phil

Hi bi3qwq. I had some problems getting your sketch to fit on my Nano (max 30720 bytes). I had to go through it trimming out lots of text etc. before I could get it to fit. Now it's installed, I can have a proper play.* The display looks great, although the bar graph and figures overflow when the antenna port is open circuit.* The encoder button and DDS module use different pins on my hardware, but this was easily changed in your sketch.* I think there is definitely a problem with the calibration routine, as your screen (for example) reads an SWR of about 7 for a measured resistance of about 150 ohms. The actual value should be around 3.I think if you can revisit the SWR calculation and calibration aspect, and perhaps investigate why it doesn't fit on some Nanos (this could be a problem ...

Hi bi3qwq. I had some problems getting your sketch to fit on my Nano (max 30720 bytes). I had to go through it trimming out lots of text etc. before I could get it to fit. Now it's installed, I can have a proper play.* The display looks great, although the bar graph and figures overflow when the antenna port is open circuit.* The encoder button and DDS module use different pins on my hardware, but this was easily changed in your sketch.* I think there is definitely a problem with the calibration routine, as your screen (for example) reads an SWR of about 7 for a measured resistance of about 150 ohms. The actual value should be around 3.I think if you can revisit the SWR calculation and calibration aspect, and perhaps investigate why it doesn't fit on some Nanos (this could be a problem with my set-up, admittedly), then it all looks really good. The bar display and the graph zooming feature are cool, and it's much easier to pick an operating frequency than on mine. Nice work...Cheersdr_phil

Hi again. I'm really impressed with your improved user interface; I particularly loved the graph zooming! I would be delighted if you would share your work with the community. Perhaps add the sketch as an attachment to a comment on this page? It's a good idea to put the calibration resistors on the board. Presumably you can switch these into the antenna port at will? Anyway, to get the calibration values you need to do a logarithmic curve fit on the measured versus true VSWR curve. I think it would be difficult to do this on the Arduino, whereas most spreadsheets have the necessary algorithms built in. I have looked at the instructions I originally posted for calibration and I think they are complete - I will try to help with specific questions however.

Hi BI3QWQ. I think you have done a beautiful job. There must have been at least $192 of labour in there, but the end result looks great. I hope it meets your needs as an analyser. I am sure a few of the people who have previously commented will be queuing up to get your schematic and PCB! I like using modules because much of the hard stuff is already done for me and they are easy to replace if I blow them up.You mentioned that you were going to rewrite the code. Which areas did you think needed changing? Please post when you are done so we can all try it out.Cheersdr_phil

Hi - really nice job! I like the transparent sun orb. It's good to see how people vary the design based on their tastes and component/PLA availability. Thanks for the positive report on the knob and for sharing the file, which I've now referred to in the main text. I'm still determined to get the crank working but when I've fixed the burned-out wires in my printer (a rite of passage, apparently) I'll probably make and fit the knob. This will make the tellurion easier to use for not-so-delicate fingers.

Hi and thank you.1. The first bevel gear STL I uploaded was incorrect, as pointed out by Styxman53. I corrected this error the day it was pointed out, so just download the bevel file again (it's got a different name, slightly).2. I also included a revised orbit arm with increased 48m1 clearance on the final page, along with some improved drive-train gears with dogs to prevent slipping on machines that have been dismantled several times.3. Have you used bigger marbles than me? I think the spindles are okay - any larger and they will detract from the appearance IMO. Hot melt glue worked really well for me and there's plenty of contact area for a reasonable bond.4. I agree but a crank is aesthetically preferable. I think the crank will work really well if some weight (not much) could be ad...

Hi and thank you.1. The first bevel gear STL I uploaded was incorrect, as pointed out by Styxman53. I corrected this error the day it was pointed out, so just download the bevel file again (it's got a different name, slightly).2. I also included a revised orbit arm with increased 48m1 clearance on the final page, along with some improved drive-train gears with dogs to prevent slipping on machines that have been dismantled several times.3. Have you used bigger marbles than me? I think the spindles are okay - any larger and they will detract from the appearance IMO. Hot melt glue worked really well for me and there's plenty of contact area for a reasonable bond.4. I agree but a crank is aesthetically preferable. I think the crank will work really well if some weight (not much) could be added to the end of the orbit arm. I'm wondering if some washers could be embedded in the crank housing or something. Try gently pressing down on the crank housing as you work the crank and you will see what I mean.I'm delighted you are building one of these. Please post an 'I made it' photo when you are done.

Arie - that place looks great. I will add it to my list! I love this sort of stuff...

Hi Brian and thanks. I'm delighted to see you are making your own. Sorry to hear you can't find a baseplate; try looking at bread/chopping boards on ebay. Your alternative sounds good though. I considered some sort of ornate 3D printed base but my imagination failed me. Ultimately I just wanted to finish the job quickly and didn't want the base to distract from the mechanism. You will need to ensure that the base is fairly substantial, otherwise working the crank will just make the whole tellurion shift around which would be very annoying.I think that 'rounded section' of brass you refer to is the bearing assembly for the orbit arm. It actually shows (on my original) a piece of 7 mm tube x ~10 mm long surrounding the sun axis of 6 mm OD. In practice there should be no gap between the or...

Hi Brian and thanks. I'm delighted to see you are making your own. Sorry to hear you can't find a baseplate; try looking at bread/chopping boards on ebay. Your alternative sounds good though. I considered some sort of ornate 3D printed base but my imagination failed me. Ultimately I just wanted to finish the job quickly and didn't want the base to distract from the mechanism. You will need to ensure that the base is fairly substantial, otherwise working the crank will just make the whole tellurion shift around which would be very annoying.I think that 'rounded section' of brass you refer to is the bearing assembly for the orbit arm. It actually shows (on my original) a piece of 7 mm tube x ~10 mm long surrounding the sun axis of 6 mm OD. In practice there should be no gap between the orbit arm axis and the spacer above it, but then this detail would be lost from the schematic. Good luck with the build and please post an 'I made it!' when you are done.

No problem - it was the least I could do after you went to the trouble of making it all!I have added dogs to some of the gears and shafts in the drive chain which has eliminated the occasional slippage. I didn't want to use adhesive as it's effectively irreversible, whereas these gears can still be removed in principle (with a screwdriver blade). I will add an extra page to this instructable with the revised parts and also a new orbit arm with extra clearance for the 48m1 wheel.

Wow! What an amazing piece of work and faithfully reproduced so fast, too. Thanks for your kind comments. I have checked out the files that I uploaded and I put the wrong version of the bevel gear on the page, so I'm going to correct that now. It should be 12bevel.stl. Sorry about that and well spotted. If you want to check operation just wind the 54/11 gear clockwise with your fingers. You will get plenty of torque this way. I am experimenting with a modified drive arrangement that will get rid of the occasionally slippage of the bevel gears on their shafts and will post when I have it.Beautiful job, again....

Hi and thank you. I don't have any videos at present but will look at making a short one. I think donating a tellurion to your local school is really laudable. This version is quite a delicate machine though, so you'd need to consider what the likely usage might be (or be prepared to make plenty of spares!).

Thank you. I am a bit limited on free time so my typical working pattern was to design a new or modified part every Friday late afternoon and set it running on the printer during the evening. Then I'd have the rest of the weekend to incorporate it into the tellurion. Even so, the most complex part probably only takes a hour and a half (at the speed I print). Take it slow and enjoy it. You can build a simple version (just showing how the months work) with a subset of the parts, to keep you motivated...

Thanks! I think these devices are more for casual demonstration of phenomena than for making predictions, so I didn't really consider a motor to be necessary. I also didn't want to mess around with power supplies, switches, wiring etc. which would detract from the overall appearance of the device. I'd also need to shift the drive from the circumference to the sun axis. This job was effectively a feasibility study for an astronomical clock build that stagnated a few years ago. My plan for that device is to have an earth-centric depiction of the heavens that will be motorised and will reflect the current state of the sky. Watch this space...

Thanks. I think it's a pain to have to rotate the earth because a day is 1/365th of a year and the gears involved can get onerous. Nevertheless, when you see it going with the earth whizzing round it's definitely worth the effort...

Thanks for your kind comments. I should probably have varnished the baseplate before I published but I was worn out by that stage!

Thanks Yoruk.

Now that would be an interesting challenge, but not for me! :-) Thanks for the kind words, anyway!

Thank you very much. The module 1 gears have quite small teeth (~3 mm pitch around the circumference) so you'd need a very dense wood to do it. You could always scale everything up I suppose. Then there's the press-fit bearings, which might also be more challenging in different materials. Perhaps start with PLA to get the orrery bug out of your system! You might decide that it's sufficient to tick it off your 'bucket list'. Best of luck and please post an 'I made it!' when you are done, whatever medium you go for.

Thank you. Yes, I thought about it. The sun tube is hollow so it would be an easy matter to route some wires through to an LED or something similar in a hollow yellow orb. I wanted to keep it all low-tech and hand-powered though, not wanting to mess around with wires and batteries, which would need a thicker baseplate, on/off switch.... and I'd already paid for the Sun marble!

Yes you could, in principle, but in practice it would need some modest redesign. A motor would naturally sit in the centre so you'd need some form of drive arrangement coming over the sun tube, terminating in a bevel gear to drive a radial shaft which works the 12m1 bevel gear through a second 12m1 gear. Then you would do away with the crank.I thought about using it as a living almanac but it wouldn't be proof against gears slipping on their shafts. Also, it's an easy matter for someone to set up all the positions correctly then just turn the handle once each day.

Thanks WannaDuino - have a go at making one yourself!

Thank you and I wish you well with your own version. Please get in touch if you need any help.

Thanks for your kind comments. I'm glad it's off the bench now so I can look at something else...

Good work - you are clearly more patient than me! I said I would do something similar probably a year ago, but never got round to it. So sincere thanks for getting me off the hook! :-)

HiYep I'm sure these will be fine. I think I used 47Rs instead of 50Rs. This is not a high precision instrument, after all. Cheers...

Hi PaoloI only just noticed your questions. You do have to replace the 3rd and 4th values as they appear in the relevant line of the array declaration. These are referred to as columns 2 and 3 in the text because the first column on Arduino IDE is column 0. Sorry for the confusion - I might clarify this. Anyway, it sounds like you sorted it all out in the end. Good work and I hope you find it useful...

Hi Robert - interesting to hear that you've successfully modded a DDS module (have you published?). It's really hard for me to help remotely on this one, particularly without screenshots etc. The best I can suggest is that you attempt an all-band sweep and monitor the serial output. At least you can determine whether it's the display routine or the maths which is not working properly. Let me know how you get on...

Oh yeah - sorry. You need the adaptor to go from the nano to the rear panel, so it's a mini plug. I'll correct the text.Thanksdr_phil

Hi PaoloV22I couldn't get this one (it's on a little PCB, correct?) to work reliably with the existing code, which annoyed me because it was cheap. Currently the code needs a two detent per step encoder, because I borrowed someone else's code to use it. Since then I've worked out how to get a standard encoder to work but haven't bothered changing the code. You should be able to hack it without too much trouble I think.Cheers,

Hi hl2daa.Looks fantastic - it's amazing to see someone on another continent using my instructable and modifying it for their own ends, particularly as those broad-band graphs with multiple resonances look really good!I probably haven't quite caught the meaning of everything in your message but please ask again if I have missed anything.Cheers

Thanks - mine haven't collapsed yet! Not even close, as far as I can tell!

Hi Edward - you could probably substitute the high-side PNP transistor switch with a relay, if you wanted a conceptually simpler circuit (albeit with an extra wire). The transistor method really is easy though (even I could manage it...!). I don't know how the current draw would compare between a transistor and a relay coil, however, but suspect that the relay will be more power-hungry.Good luck.

Thanks Paulo. Sounds like you made it? If so I hope you find it useful (and worth the effort of building!).I have just updated the firmware to include 160 m and 60 m (and all the bands still just about fit onto the OLED display). When I've done the calibration I'll upload V7. Watch this space...

Hi Chris - thanks for letting me know. I hope it proves useful to you. I've bought a phase-sensitive detector module from ebay recently which I'm planning to incorporate into the design instead of the bridge. Watch this space (eventually!).As far as the box goes, I just picked sometime that looked okay off ebay uk. It's broadly classed as an instrument enclosure (abs body with aluminium ends). I don't think it was branded in any way. Just looking at the layout of your board, you might be better off using a simple acrylic (plexiglass) sandwich with holes for the encoder and the antenna connector. Use PCB standoffs to support the plates. You get screen protection for free if you do this!Thanks again...

Good work and thanks for letting me know! Did you reverse engineer my stripboard layout or do your own from the K6BEZ layout? I'm guessing that the arduino is hidden underneath the copper groundplane?

Hi Steve. You make some excellent points. I like the idea of an in-built cal routine (but I have to remind myself all the time that better is the enemy of good enough!). Anyway I've just found out how to extract the hex file and will email you one if you want (if it's not a breach of protocol and I can figure out how to attach stuff!).I tend to put my projects together with cheap, compact Nanos and other import modules. Once the firmware is finalised I box it up and do nothing except change the battery occasionally. Your point about the OLED is a good one - in the driver file there is a huge range of options and you almost have to guess which display you have. It's worth it though, as these are crystal-clear, bright displays and even the graphing works well - I'm not sure how a classic ...

Hi Steve. You make some excellent points. I like the idea of an in-built cal routine (but I have to remind myself all the time that better is the enemy of good enough!). Anyway I've just found out how to extract the hex file and will email you one if you want (if it's not a breach of protocol and I can figure out how to attach stuff!).I tend to put my projects together with cheap, compact Nanos and other import modules. Once the firmware is finalised I box it up and do nothing except change the battery occasionally. Your point about the OLED is a good one - in the driver file there is a huge range of options and you almost have to guess which display you have. It's worth it though, as these are crystal-clear, bright displays and even the graphing works well - I'm not sure how a classic 'lined' LCD would work. Much of my stuff ends up using every pin so I'm a bit of an I2C fan. This project has quite a few pins left over at the moment.I'm keen to update this device to measure the magnitude of reactance, so I can plot minimum SWR and reactance null simultaneously. If it's easy it could happen quite quickly. If not, I'll move on to the next project in my brimming in-tray! Watch this space.Best regards, dr_phil

Type "30dB low-noise LNA Broadband Receiver Module RF Wideband Amplifier 0.1-2000MHz" into ebay and you should get a few hits. I couldn't find a part number.I should stress that I make no recommendation as to the suitability of this device (as mine hasn't arrived yet). I think the problem of detector non-linearity will remain at low return signals. In my opinion the software-based calibration described in the instructable is the easiest and cheapest way to go. It is also fully supported in the sketch (version 6).

I'm not familiar with this method of flashing the Arduino; it sounds very sensible for a production-type environment. In this instance I think the user community is best served by compiling from source, so they can calibrate the measurements, understand the code and customise the device if they wish.

Hi Ambroigo,I've put additional information on Steps 2 & 3 which shows where to connect the screen and encoder to the Arduino. D2, D3, A4 & A5 must not be changed (because they provide hardware interrupts & I2C support). The other digital pins to interface with the DDS etc. are optional and can be changed in the sketch.The sketch (.ino) automatically interfaces with the OLED and encoder. When performing a single or multi-band scan, frequency and VSWR values are sent out of the serial port on the back of the unit. The easiest way to get these is to connect up your USB Arduino Uno-style programming lead and start up a 9600 baud serial monitor via the Arduino IDE. Then copy and paste the results into a spreadsheet.

er, sorry - Step 2!

Hi and thanks. I will look at producing a schematic as there is a lot of unexpected interest. Nevertheless all the detail is in the instructable if you look carefully.

Hi. You can find the schematic for the basic VSWR capability via the link on Step 3. Look on Page 7. This doesn't include the encoder and the screen. I didn't expect this project to create such interest so I will have a look at creating a comprehensive schematic for the whole system. It will take a little while though...

Hi. See http://www.hamstack.com/hs_projects/k6bez_antenna_analyzer.pdf. Page 11 refers to a simple resistive bridge. I think the implementation on the board is more complex as Page 11 only shows a single diode. I haven't gone through it in detail, but I'm glad it seems to work!

Thank you. If you want the schematic, check out K6BEZ's website for his original circuit, which I've borrowed largely unchanged. I have however added the rotary encoder and the screen etc. which hopefully any Arduino fan should be able to follow or adapt to their own specification. If not I'll try to answer specific questions. For what it's worth, it usually takes me ages to transfer a schematic onto stripboard and I'd love it if someone did that job for me; it's interesting to see so many people wanting it the other way round. :-)

Thanks. I didn't present the schematic because a) the fundamental VSWR part is K6BEZ's work and is documented extensively on his site; b) the idea is to tell you how to make one of these, not go into the detailed function of the system. Hope that makes sense :-).

Yeah, I just love those OLED displays - small but very clear and easy to read.You could probably convert this if you a) had an appropriate DDS module covering the relevant ranges; b) your resistive bridge (see comments above),and associated circuitry and wiring were appropriate to the higher frequency. If all that's okay (and I've no idea whether it is), you just need to change the contents of the array that stores the HF band information.If you do it, please publish!

Hi again. Thanks for the tip; it certainly sounds very easy (once you know how). In my defence I don't have a key. I'm working on learning CW but haven't got far enough with Koch to justify buying one yet.

Hi & thanks for your interest. I'm really sorry but I couldn't face making another one. It took me several months (off and on), but in fairness most of that was getting the code right (and making the rotary encoder work properly). The good news is that bit has now been done for you. It's really easy to build a bare-bones version (two or three hours work) and you just need to put my sketch onto it.Alternatively you may wish to consider one of the very cheap Chinese units from Ebay?

Thank you. Sounds like you have way more experience than me in the field (that's not hard, mind you!). I'm usually really pushed for time and the finer points of antenna design and tuning are beyond me at the moment. I spent out a load on a new rig and didn't want to trash it with my inexperience! Hence the analyser, which gives me peace of mind and saves me time if and when I change the antenna.Your DDS seems has demanding supply requirements. The one I used cost about £6.30 and uses a 5 V rail. It will go up to about 40 MHz. Good luck with the project though.

Thanks. Erm, seriously I would probably buy the cheap Chinese analyser for about £45. Getting my basic system working was pretty easy, but making it work well and look nice took ages. What's your time worth? Like all these things, it's economically usually a bad idea but you learn loads and get lots of satisfaction.The encoder is really nice but honestly, it would have been much cheaper and quicker to use push-buttons.For a future build it might be nice to try to incorporate resistance and reactance measurements, but at the time it was all about not blowing up my finals!

You're welcome and thanks for your kind words: sharing has helped me hugely so I try to put something back. The TV isn't getting much use at the moment so you'll have to wait for all those additional features I talked about... perhaps consider them a challenge and post your results when you've done them?! Good luck with Arduino...

Excellent work Simon - thanks very much for sharing. Adding to Githyuk's observations, I have also found that this works well with a two detents per pulse encoder. I previously tried a KY-040 'module' with a 20 pulse/20 detent device, and performance was too jittery for a menu system. This is a bit of a shame as the 30/15 devices are relatively expensive (~£6 or more), especially if you want a switch and a threaded body. Now if we could just figure out how to get the cheapo ones to work... :-)

Hi. Simply find the line in loop() which reads 'timeWindow=0' and change it to 'timeWindow=1'. Then the display should read 'xxxx tAG' all the time and all users can log in any time.Cheers

Hi. The concept is as follows:Let's say you have two kids and you think they should probably be allowed up to 2 hours of TV a day. This is already coded but you can change it.Let's also say you don't want them watching TV in the morning before school, and after about 6pm when they should be eating and getting ready for bed. These time 'windows' can also be coded separately for Mon-Fri and weekends.The kids will be able to watch TV when a) they have minutes on their 'account'; and b) when the time is in a permitted window (e.g. 3pm to 6pm). When these conditions are met, they still have to swipe their tag to 'log on' and switch on the TV signal.You know when the timer is in a permitted window because it says 'tAG' instead of 'off'. When it says 'tAG', the kids can switch on the TV signa...

Hi. The concept is as follows:Let's say you have two kids and you think they should probably be allowed up to 2 hours of TV a day. This is already coded but you can change it.Let's also say you don't want them watching TV in the morning before school, and after about 6pm when they should be eating and getting ready for bed. These time 'windows' can also be coded separately for Mon-Fri and weekends.The kids will be able to watch TV when a) they have minutes on their 'account'; and b) when the time is in a permitted window (e.g. 3pm to 6pm). When these conditions are met, they still have to swipe their tag to 'log on' and switch on the TV signal.You know when the timer is in a permitted window because it says 'tAG' instead of 'off'. When it says 'tAG', the kids can switch on the TV signal by swiping their RFID tags. Then their minutes start to count down, till they swipe again and log off / switch off the tv signal.A parent or holder of the timer tag can use the TV at any time (you pay the bills, right?). Only normal users (i.e. kids) have to wait for 'XX:XX tAG' to appear.Hopefully this make sense. Perhaps I need to check my write-up...Cheers

Thanks for your kind comments. It is, as you say, exactly what it needs to be (for me, anyway)...