Tasmota to drive two sets of LEDs on 1 wire pair

[Paul Faure]

Hi all,

I am playing aound with some LED lights that are connected to a single strand (2 wires). The LED strand has 4 colours on it, green, red, white and blue, all connected to the same two wires. A positive 4v turn on two colours, a -4v turns on the other two. A PWM signal from tasmota can dim the colours. The existing LED driver can turn on all the lights at once, fade them in and out or blink them.

I am trying to connect the lights up to a NodeMCU board and had some success with turning on either the red and green, OR the white and blue. But I can't them them all on at once.

The output voltage across the two wires when all lights are on is 0v (as expected if it's cycling the voltage from positive to negative quickly)

How can tasmota switch between two different PWM signals so that the frequency is the same but offset so they don't conflict?

I have attached images of the original LED driver. It runs off 3xAA batteries.

Many thanks

Paul

[Philip Knowles]

A NodeMCU can't produce a negative voltage. It's outputs are either 0V or 3.3V. PWM changes the time that the voltage is on for.

If you used an NPN transistor to drive one output and a PNP transistor for the other you may get it to work but this isn't Tasmota it's electronics. You may need a -4/0/+4 power supply or use a voltage divider to get a centre virtual 0V but it's guesswork.

Sorry

Phil K

Get Outlook for Android

---

From: sonof...@googlegroups.com <sonof...@googlegroups.com> on behalf of Paul Faure <paul...@gmail.com>
Sent: Saturday, November 13, 2021 5:18:00 AM
To: TasmotaUsers <sonof...@googlegroups.com>
Subject: Tasmota to drive two sets of LEDs on 1 wire pair

 

--
You received this message because you are subscribed to the Google Groups "TasmotaUsers" group.
To unsubscribe from this group and stop receiving emails from it, send an email to sonoffusers...@googlegroups.com.
To view this discussion on the web, visit https://groups.google.com/d/msgid/sonoffusers/f25bbb65-c1ca-4d22-9dcb-a9ec09f0d519n%40googlegroups.com.

[Paul Faure]

Thanks Phil.

I can use a couple of transistors with PWM to drive the two sets of LEDs (each connected to a GPIO). Independently that's not a problem.

I will try a third GPIO with PWM to control which of the two GPIOs drives the line. There will be some AND logic there, when 1 line is ON, the other must be OFF.

I am guessing there is no way to fine control the PWM signals in software.

 

[Philip Knowles]

You may be able to use a Rule based on the 3rd PWM without any logic and 2 triggers one pwm3#state <512 the other >512

<512 do var1 512; var2 %value%; sub1 %var2%; mult1 2; pwm2 0; pwm1 %var1% endon

>512 do var1 %value%; sub1 512; mult1 2; pwm1 0; pwm2 %var1% endon

=512 do pwm1 0; pwm2 0 endon

States of pwm3

0 512-0=512 512×2=1024 pwm1 1024 pwm2 0

256 512-256=256 256×2=512 pwm1 512 pwm2 0

512 pwm1 0 pwm2

768 768-512=256 256×2=512 pwm1 0 pwm2 512

1023 1023-512=511 511×2=1022 pwm1 0 pwm2 1022

Not tested

You could also use a potentiometer

Regards

Phil K

Get Outlook for Android

---

From: sonof...@googlegroups.com <sonof...@googlegroups.com> on behalf of Paul Faure <paul...@gmail.com>

Sent: Monday, November 15, 2021 3:31:40 AM
To: TasmotaUsers <sonof...@googlegroups.com>
Subject: Re: Tasmota to drive two sets of LEDs on 1 wire pair

 

To view this discussion on the web, visit https://groups.google.com/d/msgid/sonoffusers/7a70b624-6052-4b02-b9e6-3b8ddbf90150n%40googlegroups.com.

[Paul Faure]

Thanks for the suggestion. I will give it a shot, it will save me some transistors :).

[Paul Faure]

For those curious about the solution, I used some and gates to merge two PWM signals, and an H-bridge to drive the LED string in both forwards and negative voltages.