I thought I would make a PWM to test the Cybex Tread board. That to give it the speed input signal. So searched and decided the to simulate the circuit.

Since like for ever Multisim has been giving me timestep error, I dedicated quite a few investment on to finding out the reason and all paid off. it was the XP SP3 CD that I use created the run around. Any machine with SP3 wil give u a timestep error and will not simulate any Multisim circuit.

Oh well !! that's solved, back to the circuit.
I simulated the circuit in V11 and see the 555's pin3 connection to the fet.

It was not like tht before, but when I hit "RUN" , the 555 model changes to the one u are seeing above.

Is it telling me that I blew my Timer?

 

Did it also come with the little puff of smoke? I had to deal with that with students in a lab. They all thought it was funny until they couldn't stop it from happening. Turns out the resistors they simulated with were marked at 0.25 W and they were simulating a circuit with 50 A.

Are you exceeding the allowable current from the 555?

 

Ooops ! My mistake it works..
But as not intended....
Needed to replace the 555 Model

 

Well, duh! There was a piece missing!

 

Well, duh! There was a piece missing!

DUH!!

Kekekekekk!!!

I got the thing working as I wanted. The 500K VR value is critical.

I can change the frequency from 1 Hz to 500Hz by simply switching the capacitor connected to the trigger...

Hmmm!! I can make a test pulsing thingy like this ..NO !!

 

Your threshold and trigger should be connected together in the 1st circuit you posted. There is a junction missing.

 

Your threshold and trigger should be connected together in the 1st circuit you posted. There is a junction missing.

Ya....I figured that out a bit later..