I'm trying to control a pump with pwm signal generated by ni9474 Digital output module. The pump uses 24v and has a 0 to 5v active low pwm signal to control the speed, the threshold when the pump turns on and off is 0.97v. The problem is that when I connect the pump to the 24v power supply there is 4.5v coming form the signal pin. In order to clean the square wave generated by the ni9474 I connected a resistor from the signal to com. Since the pump needs to see low voltage or below 1v to turn on, the constant voltage that keeps it off does not allow for my pwm signal to drop below the threshold. I used 10k Ohm resistor how the ni9474 manual recommends to clean the square wave, but that dropped the constant voltage to 1.5v. I can see the signal but it does not drop enough to turn off and on the pump. I used a 3k ohm resistor to drop the constant voltage below the voltage threshold, but it is active low and it always turns on. when I connect a waveform generator there is the 4.5v constant voltage but when the output is turned on it changes to the waveform generators output. Is there a way I can make the pwm signal generated by the ni9474 also do that?
