simulating a timer circuit - Electronic Circuits Projects Diagrams Free

ulot · 14th February 2006, 10:40 AM

i tried to simulate a 555 timer circuit in monostable mode and it didn't seam to work right. the astable version worked very fine but with monostable didn't ever go off it just stayed on. sorry i couldn't get the circuit to post but i went over it again and again the only thing i noticed was that i didn't use a touch switch but a on/off switch which was all i could get using Multisim. so once the switch closed, it stayed down and the output continues constantly past the time and once the switch was opened, the went back to zero. what could the problem be?

Roff · 14th February 2006, 04:04 PM

Your problem is the switch. It has to close, then open before the end of the pulse. I don't use Multisim, but all versions of Spice have a voltage-controlled switch which you can use. You may already be using one, but not controlling it correctly.
Your other alternative is to place a differentiator between the switch and the monostable. For an example, see the third schematic from the bottom of the page (555 timer Mono stable (one shot) circuit) at this site.

ulot · 18th February 2006, 03:54 PM

thanks ron for your help the mono is working now but i've got another problem. i'm trying to power the timer circuit form the same AC mains as the circuit it is triggering. it worked fine when powered by a reperate DC source but when i try to use a rectified voltage to power it, i get errors so i tried to create a power pack reperately and kept gettig errors the moment i put a load across the filter capacitor. i've checked the Inverse volatage of the diodes and everthing i know how but i doesn't seam to work. the ciruit is was built using multisim so if anyone here knows how to use multisim could you please help me out?
i've included the shematic and the error message i encountered.

Roff · 18th February 2006, 04:59 PM

I think most versions of Spice need a ground symbol, although you virtual scope may provide that. As I said, I have no experience with Multisim. Try it and see if it helps.

ulot · 20th February 2006, 08:36 AM

i'll try the ground too but if anyone else uses multisim could you please help me out?

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14th February 2006, 10:40 AM	(permalink)
ulot	simulating a timer circuit i tried to simulate a 555 timer circuit in monostable mode and it didn't seam to work right. the astable version worked very fine but with monostable didn't ever go off it just stayed on. sorry i couldn't get the circuit to post but i went over it again and again the only thing i noticed was that i didn't use a touch switch but a on/off switch which was all i could get using Multisim. so once the switch closed, it stayed down and the output continues constantly past the time and once the switch was opened, the went back to zero. what could the problem be?

14th February 2006, 04:04 PM	(permalink)
Roff	Your problem is the switch. It has to close, then open before the end of the pulse. I don't use Multisim, but all versions of Spice have a voltage-controlled switch which you can use. You may already be using one, but not controlling it correctly. Your other alternative is to place a differentiator between the switch and the monostable. For an example, see the third schematic from the bottom of the page (555 timer Mono stable (one shot) circuit) at this site. __________________ Ron

18th February 2006, 04:59 PM	(permalink)
Roff	I think most versions of Spice need a ground symbol, although you virtual scope may provide that. As I said, I have no experience with Multisim. Try it and see if it helps. __________________ Ron

20th February 2006, 08:36 AM	(permalink)
ulot	i'll try the ground too but if anyone else uses multisim could you please help me out?