Hi Guys

Trying to use orcad to simulate some circuits and i am struggling to get anything to work.

Ive done some searching on here and found alot of questions relating to orcad.

If OPTIKON or STYX could offer their advice here that would be great as it appears you have some experience using this package from reading old posts.

Basically i can build my schematic, start a new simulation, but i get no output at all. I place probe where i want to measure but the output is a flat line on zero volts.

I want to try and simulate a 555 timer but am unable to get an output. I tried a very very simple circuit to see if that would work and i get the same result.

I assume its my library files or something.

here are some photos to show where i am at and hopefully i can get soem help.

cheers

Andy

Attached Images

	simoptions.jpg (120.4 KB, 362 views)
	sim1_207.jpg (111.8 KB, 362 views)
	circuit1_134.jpg (109.5 KB, 362 views)

 

can anyone see where i am going wrong. This is a simle circuit just to try and figure out why its not working.

Thanks

Andy

sorry pics are not in order but you can get the general idea if you have used orcad before.

Attached Images

	output_186.jpg (140.3 KB, 355 views)
	libfiles.jpg (121.0 KB, 354 views)

 

Try to place a VSIN generator with AC = 0, DC = 0, VOFF = 0, VAMPL = 10, FREQ = 50 and you will see a sine wave.

 

The 10 VAC generator is only good for frequency sweep analysis (AC).

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thanks for the answers,

my main problem is to simulate a simple 555 timer (astable)

however this seems harder than it seems.

Has anyone ever simulated a 555 timer succesfully using ORCAD?????

thanks

Andy

 

Check your PM

 

Thanks Optikon greatful for your reply. Here is the output file as you suggested.


I get an output wave but its nothing like expected or what it should be.

Thanks

Andy

Attached Files

555_timer.txt (4.2 KB, 44 views)

 

Hi Andy, post your schematic. If you don't have floating pins, then I think that you're using a Vdc as the power supply and that is not good for your circuit

 

That shouldnt be a problem? Other than it looks like it is at 0 VDC.

 

Yes its very strange why its not working. Seems odd that such a simple circuit cant be simulated.

i still hope its a silly mistake somewhere, sheeesh running out will power here.


here is the circuit for whoever asked for it.

YES i am using a VCD source, why is this bad??????????????

Andy

Attached Images

555_144.jpg (54.6 KB, 210 views)

 

Actually its working now and i have no idea how. I am using the demo verison at work where previously i have been using my own copy at home. So maybe something with lib files??? - i will check it out

I get my square wave output now at the correct frequency but i have noticed that the output voltage is only 1V???????

The timer is supplied from 5V

any suggestions?

Andy

 

Hi Andy, if you breadboard the circuit, it would work.
You should load pin3 with a 10k resistor, because you can't leave floating pins with SPICE.
Then, as I told you, the VDC generator is not good for this circuit.
In real oscillator circuits the oscillation starts because you turn the power on. With SPICE you must emulate that event. The voltage of your generator must be 0 at t=0 and then rise to 5 V. You can do this with a VPULSE generator. Place it instead of the VDC generator.
Set DC=0, AC=0, V1=0, V2=5, TD=10m, TR=100n=TF, PW=8s,
PER=10s.
For the Transient Analysis Setup, set Final time=5s (you will see 4 periods, since fo=1,1 Hz). Dont'care of the first period that is different because of the initial transient.

 

The output swings between 0 and 3.7 V

 

If startup is an issue, it is easier to just use an initial condition of a state that is opposite of what it starts up as.