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LDR

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mstechca

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Since my last question didnt get the answer I was looking for, I shall ask this:

How do I make a 1 transistor (BJT) oscillator which makes a sound under bright light and no output under darkness? I have an LDR which can detect light. Once again, I dont want to use IC's.
 
mstechca said:
Once again, I dont want to use IC's.

Why not?.

Using IC's will make a simple effective project. Doing it without IC's will require many more components and probably give worse performance.

Limiting it to a single transistor probably makes it impractical - and if not it's certainly likely to make it difficult to reproduce.
 
Hi MS,
Here's a gated oscillator for you to connect your LDR to its gating input and the positive supply, and a resistor from its gating input to ground.
I think it will stop when the LDR is in the light. Reverse the LDR and resistor.
 
I'll try that one. thanks
 
I didn't think that circuit would produce a sinewave, so I simulated it. Damn, it works!

V2 is a single pulse to get the oscillator started because simulators don't have noise that starts real world oscillators.

V2 being zero does not stop the oscillator, however.
 

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Hi Russ,
Yeah, that oscillator takes a while to "get up to speed".
Like I said, I think the author got the control input function backwards, a high stops it.
 
It worked for me, but I had to play with the values of the capacitors and resistors.
 
hey russ, I don't knwo if someone already told you this, but you don't have to print out the picture and then scan it. Is that what you're doing?

Just click on the swcad window, hit ctrl+c (copy). then go to paint, and hit ctrl+v (paste). its that simple! and its in color, so it is easier to differentiate between different signals.
 
Russlk said:
Thanks, Zach. I can get either the plot or the schematic, how do I get both?
You have to do them as two separate files. Click in the waves window and do ctrl-c to copy the waveform. When you post them, add one as an attachment, do a preview, then click on "browse" again to post the other one.
 
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