Need PWM circuit that outputs ground output instead of power

Thread Starter

Cam2363

Joined Feb 2, 2018
15
Working on a gauge cluster and to make the speedometer work, and it changes value when I connect the wire to ground and then remove it. So if i do that quickly it changes the value but if I do that with power, nothing happens.

So basically I need a circuit that alternates between ground and open circuit

Thanks!
 
Last edited:

wayneh

Joined Sep 9, 2010
17,155
A PWM output alternates from near ground to near the positive power rail. I hink what you need instead is something that alternates between open (no connection) and ground.
 

Thread Starter

Cam2363

Joined Feb 2, 2018
15
A PWM output alternates from near ground to near the positive power rail. I hink what you need instead is something that alternates between open (no connection) and ground.
Yes thats exactly what i need. Just wasnt exactly sure how to describe it. Know any circuit for that?
 

wayneh

Joined Sep 9, 2010
17,155
You’re close. Use the 555 output to drive a transistor. That will be like switch and the 555 can flip it on and off as fast as you like.

Now that I think about it, the 555 may have such an output (open collector) built in. Pin 7 maybe. I’m away from my laptop but maybe someone else will jump in.
 
Top