Transistor monostable multivibrator circuit - Drive low signal device - Rev 1

125

02:06:24

One shot non retriggerable pulse extender
Drives low signal device (right hand side)
Input is simulated with 1 second cycle (left hand side)
Input has options to be forced on or off for diagnostics

68k resistor limits current leak from low signal device back through T1.
(68k is probably overkill and 56k or lower would suffice in a real circuit)

published 11 years ago

Sine_eyed

11 years ago

This circuit isn't acting as a monostable- the output follows exactly what either source is giving. 50% width of a 1 second pulse when the square wave generator is selected, and selecting the DC source/switch combo the LED lights on and off following the switch as it is toggled. The output, after receiving an input pulse, should have an "on" duration independent of any subsequent input pulses- until that duration has ended of course. Check your notes and hit that drawing board- I'd like to see you get this one going!..

ozfalcon

11 years ago

Ok, I have fixed the circuit. But I'm not sure using 68k resistor is an optimal design................

Sine_eyed

11 years ago

Yep, good job- you got it working! It seems there was no need for that other switch in the middle of the circuit- now we can see the output pulse by selecting the square wave generator or the DC source and toggling back and forth between it and ground. The output signal can be varied by changing the values of the R/C element tied to the base of the lower transistor. Changing the capacitor from 10 to 100uF will give us a nearly one second output, for example..

ozfalcon

11 years ago

Yes the switch (removed) in the middle of the circuit was not needed. It was a diagnostic to see how much current flowed to T2 base.

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