Christmas Light "Mimic" Circuit

Hi all, I have been thinking about this project for some time and know that I lack the experience in a key area regarding AC voltage.

I have several sets of christmas lights that I put up around windows and doors on the front of my house that are multicolor/multifunction lights. What I would like to do is synchronize those sets of lights. I have already used wireless comms for Halloween decorations so have a basic idea of how to achieve what i want.

The problem for me is that the lights are controlled by a small microcontroller chip that fades/flashes each color strand according to the multi function program. I have measured and each strand was running about 33 volts AC if I recall at full brightness.

My idea is to measure the AC voltage of each strand, transmit that wirelessly to controllers at the other strands and reproduce the color/brightness levels.

I just have no idea how to measure AC voltage or achieve that goal. The only other thought I have had on this would be to measure the voltage at the transistor PIN controlling the lights power voltage. I just don't know how to do that as its all AC power.

Thanks for any thoughts/insight.

Please, info about the the unit/driver of the lights. AC sounds strange. If it is PWM controlled You have a square wave signal. Not all multimeters manage to measure that correctly. A wiring diagram would likely help us.

So my original measurements were of an incandescent set. I recently purchased some LED sets and they are very different inside. I should have started this thread with those. I just opened up one of those controller boxes and was surprised to read 102V DC at each strand leg when they were solid on OR 54V AC?

At any rate attached are some images of the board. It appears to be a 4 rectifier AC/DC conversion with a controller chip controlling the diodes at the output end

Closeups: Input Diode:

Output Transistor:

Control Chip:

flyerdp:
I just have no idea how to measure AC voltage or achieve that goal. The only other thought I have had on this would be to measure the voltage at the transistor PIN controlling the lights power voltage. I just don’t know how to do that as its all AC power.

Thanks for any thoughts/insight.

Forgive me, but you seem fairly new at this. I think you should give this up. Playing with high voltage is something that you need to work your way up to. It’s not just that you could hurt yourself. It’s that other people might be injured or killed.

You're "cutting it close" for Christmas 2020... If you were simply modifying your Halloween display you could probably do it, but since you are here asking questions... I'd recommend saving the wireless stuff for last. If you run out of time, maybe you can make it wireless next year.

It's often easier to build from scratch than to "hack" something.

You'll most likely have to scrap the existing controllers and just use the lights. If they are LEDs (and I assume they are*) LED's run on DC but it could be PWM or rectified and unfiltered AC.

If they are individually-addressable (probably not) they are probably WS2811/WS2812 (Neopixels) which have one data/control line or DotStars which have a data line and a clock connection. With either of those you just need the microcontroller and a power supply. The software is complicated, but there is a library, and the hardware is super-simple.

If only the colors are controlled (all of the red LEDs come-on at once, etc,) then you need a power supply and a MOSFET driver for each color. Ideally, you should use a variable DC power supply and bring-up voltage slowly until the brightness about matches the current brightness. Then measure the voltage & current so you can select appropriate permanent power supplies and choose an appropriate MOSFET to handle the current.

* P.S. Relays can switch AC or DC (including power line voltage) but they don't dim. Regular relays require a driver circuit for the coil (the Arduino can't supply enough current) but you can get relay boards with a built-in driver. There are solid state relays that can be directly controlled by the Arduino but solid state AC & DC solid state relays are not interchangeable so you have to know what you're dealing with.

...I have some older "regular AC Christmas lights" and I tie-wrapped 4 strings of 4 different colors together (spaced-out evenly) and I used 4 relays to control the colors.

aarg: Forgive me, but you seem fairly new at this. I think you should give this up. Playing with high voltage is something that you need to work your way up to. It's not just that you could hurt yourself. It's that other people might be injured or killed.

No, not even a little bit close to new. Also not new to 120VAC power. I have a Halloween skeleton that moves and is managed by 5 IR motion sensors 30 feet away in the yard sending wireless position info that has the head tracking passers by and turns the head while driving two neopixels in the eyes. I have all of the hardware and experience to do the wireless coms for up to 10 light sets I just wanted to read one set and mimic with the others. It did occur to me that I could just write the logic to run the lights and wirelessly transmit that to all the other sets stripping them of their built in controllers. Given that the control has already been created/written with numerous patterns I wondered as to the challenge of building something that could simply read one, transmit the info to a random number of others and drive the transistor to "repeat" what the master set says. This way if I find a really cool set with patterns the others could just mimic it too!

and was surprised to read 102V DC at each strand leg when they were solid on OR 54V AC?

Like Railroader says, digital multmeters only work properly with constant DC or AC sine waves. Square waves, rectified (unfiltered) AC, dimmed (chopped) AC, or PWM can give unpredictable results. The inertia of a mechanical meter movement will "smooth out" the readings giving you a pretty-good average. Or, an oscilloscope will show you the voltage and waveform.

And like I said, it's often easier to start-over with something known than to hack something unknown.

If you want to take a risk you can connect one string (or one color of one string) directly to AC power to see what happens. Or, you could try a rectifier in series first (half the RMS voltage). Probably the worst thing is is a burned-out light strip, but I'd recommend doing it outdoors on a non-flammable surface, and wear safety glasses, and maybe have a fire extinguisher on-hand! :smiling_imp:

DVDdoug: If they are individually-addressable (probably not) they are probably WS2811/WS2812 (Neopixels) which have one data/control line or DotStars which have a data line and a clock connection.

You are seriously joking!

We are here discussing Christmas lights - $10 a tub all up (or maybe $20). Read the OP and #2 - 33 V and 100 VDC.

DVDdoug: You'll most likely have to scrap the existing controllers and just use the lights. If they are LEDs (and I assume they are*) LED's run on DC but it could be PWM or rectified and unfiltered AC.

OK, here's what they do. The control logic runs on DC, so the mains is directly rectified with the bridge to DC. On a 115 VAC supply this is 150 V peak (but no need to smooth it). On a 230 V supply this would be ridiculous so they only use a switchmode (isolated) converter to drop directly to 33 VDC (10 LEDs each string branch).

Whatever the voltage, there are a number of series strings corresponding to that voltage, wired in parallel, half of them in one direction and the other half in reverse. They are driven by a high voltage H-bridge which allows each direction to be separately PWM-ed up to half of the time. (Arguably, it could alternately drive one half at a time up to 100%.) There may be current control resistors in the strings.

While it all looks easy on that tiny PCB, it is using high voltage parts (the same as in switchmode mains power converters) and cunningly designed control ASICs. Emulating these is clearly no joke, you would need a lot more than just an Arduino. :astonished:

Paul__B: ......

While it all looks easy on that tiny PCB, it is using high voltage parts (the same as in switchmode mains power converters) and cunningly designed control ASICs. Emulating these is clearly no joke, you would need a lot more than just an Arduino. :astonished:

Yeah I assumed that some more would be needed. The arduino would mainly be to run the wireless and be the logic for control circuitry.