Fan: switched GND to switched positive

dc42

The problem is that C1 has nowhere to discharge except through the device that you connect the output to. Here are a few suggestions:

In your PNP high side driver circuit, increase R2 to 10K and connect a 1K resistor from the transistor collector to ground. I also recommend adding a 10K resistor between base and emitter of the transistor.
Instead of using a PNP transistor etc. use a 74HCT02 gate connected to an expansion board heater output, gated with +3.3V, as we suggest for driving a laser PWM pin. Then connect your RC network to the output of the 74HCT02.
Use a PWM to 0-10V VFD converter (readily available on eBay), then a voltage divider to reduce the 0-10V to 0-5V.

Nxt-1

@poohzaza said in Fan: switched GND to switched positive:

@Nxt-1 said in Fan: switched GND to switched positive:

Kind of reaching end of my patience for just getting speed control working sadl

you can have a look at
1.did you jumper use external control signal
2.remove low pass fliter and conect pwm siginal then conect jumper for pwm control

can i have a look at esc datasheet

or cheak that pwm work correctly by conect mutimeter in volt mode you shoud see variable voltage when you adjust the fan siginal

I did remove the jumper for external control signal. I also tested in pwm mode and tried some pwm frequencies, without success. Sadly with these cheapo controllers, no datasheet is available (at least that I could find).

@dc42 said in Fan: switched GND to switched positive:

The problem is that C1 has nowhere to discharge except through the device that you connect the output to. Here are a few suggestions:

In your PNP high side driver circuit, increase R2 to 10K and connect a 1K resistor from the transistor collector to ground. I also recommend adding a 10K resistor between base and emitter of the transistor.

Instead of using a PNP transistor etc. use a 74HCT02 gate connected to an expansion board heater output, gated with +3.3V, as we suggest for driving a laser PWM pin. Then connect your RC network to the output of the 74HCT02.

Use a PWM to 0-10V VFD converter (readily available on eBay), then a voltage divider to reduce the 0-10V to 0-5V.

I changed the circuit as you suggested and we seem to have a winner. I did lower the LPF capacitance to 10µF, as the rise and fall time was unnecessarily long. I did notice my upper voltage limit is ~3,7V instead of the ideal 5V, but this is not really an issue as 3,7V already corresponds to a very large airflow.

Now I just need to move the components from the breadboard and neatly arrange them on a piece of protoboard.