I'm trying to design a LED circuit where a LED beings to flash after the light is turned off.
For the light detection part, I followed the design of the following ciruit, without any problems. Light-sensitive Alarm Project
Afterward, in order to make the LED flash, I used a simple astable 555 circuit, as follows: **broken link removed**
Both the circuits work without problem by itself. However, it fails to work when I join the 3rd leg of the 1st IC (the Light dependent circuit) as the input voltage of the 2nd circuit.
How am I suppose to connect the two ICs in order to make the circuit work?
You didn't say where you tied the output of the 1st circuit to the second circuit. I would suggest pin 4 (Reset) that way when the sensor is in the dark the oscillator will run.
hi,
The problem is the light/dark detector is a monostable, so it will only have it output pin3 high for the timing period, then it will go low.
While the light detector 555 pin3 is high and connected to the LED flasher 555 pin 4, the led will flash, but as soon as the light detector times out the LED will not flash
EDIT:
What is the resistance of the LDR when it changes from light/dark/light.?
It should have worked unless as Eric said the second timer is longer than the one shot in the first stage. The pulse output from the first stage is positive so the second timer is only on for 10 seconds max. Don't know about the timing for the second timer??? If you power the second stage from the first you should tie pin 4 to V+. I guess I assumed the second stage was like 1/2 second so it had a few flashes before it shut off.