astable oscillator question

Thread Starter

bug13

Joined Feb 13, 2012
1,996
as seen in picture below, when i hook up the oscilloscope to outA and gnd, I can get about 1Hz, but when I connect it to OutB, I somehow get a Sine wave, what could be wrong? I am guessing one of the NAND gate is tossed?

I should get a 22kHz square + 1HZ square wave on OutB.

note: In is always high, and the OutA on the second one should be labeled OutB

 

Wendy

Joined Mar 24, 2008
22,647
My guess is you are beating the two frequencies together, which would create a sine wave. Just a guess though. Try each oscillator separately and see what it does.
 

t_n_k

Joined Mar 6, 2009
5,455
I should get a 22kHz square + 1HZ square wave on OutB.
What's the sinewave frequency you see on the CRO - maybe it's 50Hz due to CRO signal grounding oversight.

I'm assuming you have actually built the circuit.

The output should be a gated pulse train at the nominal conditions - if the primary astable is indeed 1Hz then you would expect approx 500ms bursts at the second astable frequency [22kHz?]. However, I'd check your values do actually give those stated frequencies.
 

Thread Starter

bug13

Joined Feb 13, 2012
1,996
Sorry, the second should be around 2kHz, my mistake.

the circuit was built, I will need to go back to school to check the frequency tomorrow.

maybe it's 50Hz due to CRO signal grounding
And can you explain a bit more on this one, I think I get your idea, but I am not sure if I got right idea tho.

And another thing, how robust is a NAND gate, I am thinking I might tossed one of the NAND gate, as connect the positive to the wrong when I first hooked it up to the scope.

What's the sinewave frequency you see on the CRO - maybe it's 50Hz due to CRO signal grounding oversight.

I'm assuming you have actually built the circuit.

The output should be a gated pulse train at the nominal conditions - if the primary astable is indeed 1Hz then you would expect approx 500ms bursts at the second astable frequency [22kHz?]. However, I'd check your values do actually give those stated frequencies.
 

t_n_k

Joined Mar 6, 2009
5,455
Sorry, the second should be around 2kHz, my mistake.

the circuit was built, I will need to go back to school to check the frequency tomorrow.

And can you explain a bit more on this one, I think I get your idea, but I am not sure if I got right idea tho.

And another thing, how robust is a NAND gate, I am thinking I might tossed one of the NAND gate, as connect the positive to the wrong when I first hooked it up to the scope.
If you leave the signal ground off the circuit connection [by mistake or due to a connection fault] often you will see 50Hz [or 60Hz] mains 'noise' picked up on the CRO active. I would see 50Hz here in Australia.

If you have a spare chip it might be worth checking the problem is elsewhere rather than with a damaged gate(s).
 

Thread Starter

bug13

Joined Feb 13, 2012
1,996
I can only get 1Hz with my physical connection, but I can't even get 1Hz in multisim, is it the right connection below???

 
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