Waveshaping circuit using a 555 timer

[Ohms Law]

I have been trying to replicate this circuit for the longest. I am trying to use a 555 timer as an Astable multivibrator with a one shot IC monostable circuit.  However, when I create the circuit and use different RC combinations I actually get the correct output from the timer, but it does not cause the one shot to go active and then I can immediately hook up a multisim clock to the one shot and the circuit works fine.  Can someone please take a look at the circuit I have designed and see where I went wrong? Please see attached multisim file.

[_user32 · Accepted solution]

Ohms Law,

Sorry for the delay on this - we've been busy at the EWB group.

Your circuit was very close!   I think by not having the CLR and A inputs wired, your circuit was having problems.   Likely the CLR pin was defaulting to a logic low (which would then force Q low and Q~ high) as indicated in the datasheet.

Here is the corrected circuit (note I increased the Capacitor to give a longer pulse time on Q / Q~ since the pulse period of the 555 timer was around 250ms).  

When dealing with digital circuits, it is often convenient to hook up digital inputs to a SPDT interactive switch and to VCC (or whichever CMOS level the circuit is at) and ground as I have done here.   This gives you the ability to interactively control portions of the circuit for interactive testing...

Regards,

Patrick Noonan
Business Development Manager
National Instruments - Electronics Workbench Group

[Ohms Law]

32:

Would I do the same thing if I wanted to add a 121 one shot to the circuit that we have shown?  Oh yeah, that did work I just have to do my calculations to get the desired waveform.  Thank you a lot!

Lew