help with "oneshot" 555 circuit?

Question

i have been trying to make a working 1 shot circuit using a 555 timer and a mosfet switch.
i have simulated it on multisim but i ran into some confusion
if i select vss as my source voltage and i ground the circuit it works but if u replace that with a battery (positive and negitive) the circuit drops to microvolts and will not trip the mosfet.

here is a picture of the circuit with the power and ground
http://i51.tinypic.com/110apmx.jpg

now with the battery
http://i54.tinypic.com/fmp7bp.jpg

whats the difference im so confused

Answer 1

You've taken out R2, the 22K resistor, so the 6.8V zener is clobbering the volts on the entire circuit via the motor.

Answer 2

It looks like you need to ground the circuit with the battery too. While I am not familiar with multisim, other simulators need this ground as a reference point.



The triggering in the monostable circuit uses the trigger input, not the reset input. Normally reset is connected to VCC and the trigger input is switched momentarily to ground to trigger the device. Your circuit might work because of a race condition between trigger and reset inputs. With the trigger input floating (before the switch is operated) it may trigger the device. This may not be so with different real world 555 timers. It is best to use the standard circuits so the operation is clear.



If driving from a microprocessor the 555 might need to be held in reset by a capacitor and pullup resistor long enough for the uP outputs to be set to their initial state during a startup. This prevents false triggers by unexpected outputs from the microprocessor..

Answer 3

because of the fact the telephone agencies interior the u . s . have all agreed to no longer use 555 for any genuine telephone numbers. so as that some dumb guy or woman who's watched a action picture, would not come to a variety to aim calling it and insect somebody harmless.