Time delay in 555 Timer

[debasisswan]

Hi,
I was looking for a simple sound or light operated switch to trigger my camera flash (For stop action photography) with certain delay between triggering sound or light impulse and final switching- in the range of around 50ms to 500 ms. I found the attached circuit to be simple enough but it cannot provide me time delay between the triggering sound and final switching.

With my limited understating of electronics, I am planning to achieve this delay with certain modification in this circuit. please guide me in this. My idea is- first ii need to keep the pulse width of the 55 very long by rearranging the values of C2 and R3. Next, I will have to make a series of variable resistor (Say R8) and capacitor(say C4). Connect the open resistor end of the series at the point in between R2 and OK1 while connecting the other open capacitor end of the series to ground.

Please guide me- am I correct in my though5t process? if yes, what could be the suggested values for R2, C3, and R8, C4 (the resistor and capacitor to be used in the new series).

Thanks in advance-
Regards-
Debasisswan

[pebe]

Here is a modification to your circuit. Add the extra stage so that your existing timer provides the delay, and the extra 555 switches the flash on. Remove the existing link from Q output to R2. Then add the extra stage.

The 100K and 10uF will give about .7sec for the flash on.

[debasisswan]

Hi Pebe. Thanks a lot. Now, instead of 100K, if i put a 50K and another 100K Pot in series, shall I be able to get a delay in the range of 50 Millisecond to near 700 Millisecond?
Regards-
Debasis

[pebe]

You cannot those values with a 100uF cap.

The time T = 0.7 x C x R and the ratio for the times you want is 14:1

So using a 10uF cap you need 7.1K for 50ms and 100K for 700ms. A 5K resistor plus a 100K pot, perhaps.