I'm trying to help someone make this circuit, while also trying to get them to understand. (seems to be the harder part.)
He had a non working circuit, asking on another group and got so many conflicting answers, many saying the circuit wont work. (good chance it didn't)
So I took him offline and just doing emails.
The first thing. I got him to built a 555 oneshot. It took a while, but now we can pull pin 2 to ground and the buzzer buzzes 5 seconds. All is good.
Next I had him set up, 9v to LDR to resistor to ground, the center point is 5.6v with light and 1v when dark. Then I had him connect this to Pin 2 of the 555. Now he says it is 5.6v with light and 4.3v in the dark. (I don't really get that) He is now adjusting the resistor to pull pin 2 down below 1/3Vc.
Where my knowledge is running out is, I know Pin 2 needs to be a pulse otherwise Pin 3 stays high, (as long as Pin 2 is low). That means I need to differentiate the voltage into Pin 2. But I know a slow light to dark transition will fail with a normal differentiation. So I expect I'm going to need a circuit between the ldr and Pin 2. This fellow has a 741 and only PNP transistors. ¯\_(ツ)_/¯
Do you have an idea to turn a negative going slow voltage transition into a fast negative pulse?
Thanks all.