PWM problem. Can 1 of the output waveform from a controller be nulled and still pass a different wave form?

Thread Starter


Joined Apr 24, 2022
Hello to all,
The problem I am having is with an aftermarket turn signal/brake light module (TSM) for a motorcycle I'm trying to make work. It's designed to add functionality to the stock (TSM), which it does nicely to the rear facing lamps but not what I want it to do in the front. The new (TSM) uses pulse width modulation to dim the lights so they simulate the lower power filament of a 2 filament bulb. (for example an 1147) with only a single filament bulb. (for example an 1146). When a turn switch is closed by the operator the output cycles on/off like one would expect from a turn signal relay. The problem I have is the front lamps I have are 3 wire and not 2. I have #1 a black wire to ground, #2 a white wire connected to the headlight circuit and operates white leds in the turn signal lamp assembly. #3 a yellow wire which is connected to the output of the turn signal module and the yellow leds in the turn signal lamp assembly. The white leds are designed to operate constantly EXCEPT when the yellow wire #3 gets a signal from the TSM which then is supposed to flash the yellows only. the only thing wrong with that is the pulse width mod signal on wire #3. It causes the white and yellow leds to turn on and off constantly as if it were confused.
I've managed to make it work with a pair of relays but I can hear the coils high pitched hum (chatter) Here are the parameters I'm working with.

TSM dim mode: Vpp =12.5, Duty cycle+ = 28%, Freq = 98 Hz, Vrms = 5.88, T = 10.4 mS
TSM turning mode: Vpp = 12.5, Duty cycle = 50%, Freq = 2.36 Hz. Vrms = 12.0, T = 422mS

Giving these parameters, can anyone suggest a better solution than relays to filter/negate the dim mode and maintain the turning mode?
I was thinking maybe a band pass filter but I believe the frequencies are too close?

Thank you in advance