Hacking decorative lights to make dimmable from phone/app.

Thread Starter

clexp

Joined Nov 12, 2021
19
I previously have excellent help from here, I'll be grateful for further advice. My quesion in one line: how do I specify the transistors /FETs for PWM LED dimming with a 100 count of LED on a mains adapted power?

My daughter was gifted a set of decorative lights. Ordinarily she keeps them in a very trendy glass jar. This is mains powered through an adapter, with a normal manual switch on them
IMG_20230204_105040 copy.jpeg
She has seen lights can be made dimmable, and would like to ceiling mount them. She has asked me about this, I think this might be a possibility. Boundaries of the project are as follows.
IMG_20230204_105100.jpg
The lights are supplied from a power adapter which I believe, gives direct current at about 24 V with a power rating of 3.6 W.
IMG_20230204_111946b.jpeg
I have explored the cabling and it appears that the LEDs are set up in eight banks of 12 LEDs. I think there are 8 banks in series, each bank of 12 LEDs in parallel. Each LED has 3 or 4 cables going in and one to bypass, in a 12-LED repeating pattern. The negative of one bank becomes the positive of the next. That is a total of 12 * 8 = 96 LEDs, so 3.6w / 96 = 0.075w per LED.

IMG_20230204_112912 copy.jpeg
24V across 8 banks gives about 3v each. P = I * V, gives 0.075W / 3V = 0.025 amps per LED.

In my mind, you brighten/fade LEDs with PWM. Can you do it on multiple banks of them at a time? She wants to dim the lot at once. So doing this to the 24v supply would need more than your normal transistor. I am in the dark here. How do you spec transistors/FETs/MOSFETs/? The Transistor (?Darlington pair?) would take power from the power adaptor and signal from Arduino/equivalent.

Where do I start with the Transistors?
 

Thread Starter

clexp

Joined Nov 12, 2021
19
Oh that's super helpful. Thanks very much. I didn't know that was a thing.

I have a browse through there then. Thanks very much.
 

bassbindevil

Joined Jan 23, 2014
838
I think you can get there with an ESP module (ESP32, ESP8266, etc) and an LED driver. This RGB LED strip driver module may/will need a 3.3 to 5V level converter since ESP things run at 3.3V logic (got some, haven't tried 'em yet), or there's this basic MOSFET driver which claims to be 3.3V compatible (just ordered 5 for myself). There's Tasmota firmware for ESP devices that will be supported by phone apps, smart speakers or home automation software, and doesn't depend on servers in the cloud.

Or there's are off-the-shelf Wifi to LED modules that are Tasmota compatible; see the LED Controller category in this listing:
https://templates.blakadder.com/light.html
There's a risk with the white plastic modules that they've revised them so they're no longer Tasmotable, but the Electrodragon looks like a safe choice:
https://www.electrodragon.com/product/esp-led-strip-board/
 
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Thread Starter

clexp

Joined Nov 12, 2021
19
That is a super helpful starting point for a from-scratch effort, thanks for the links. When I google this stuff, I just don't know what I am looking for.

A Nobel prize? really?!? I am learning so much. Must come here more often!
 
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