I'm having a brain freeze...

Thread Starter

bluebrakes

Joined Oct 17, 2009
252
I'm making a delay timer for my camera.

However, i'm having a trouble coming up with a circuit to sort my problem out.

Basically, I need a circuit, where the output is low.
Once a a trigger signal has been recieved, it waits for the delay period (adjustable from 1ms to 1 second) to elapse, then puts the output to high for a period of 20ms.

I have thought about using a 555 timer in monostable mode, but I can't get my head round the fact it needs to be low, once triggered, still low until the delay period has elapsed.

ideally, I need it to be simple as possible. Although using a PIC microcontroller is looking more suitable solution.

Any advice?
 

retched

Joined Dec 5, 2009
5,207
...LED is off...
Button pressed
...user preset time elapses...
...LED lights for 20ms...
...LED is off...

There has to be an easier way to do this, but a 556 (or 2 555s),
One for the user delay to trigger the other to hold the line high for 20ms

If you were to go that route, you may consider a PIC. That way it can all be handles via software.
 

Thread Starter

bluebrakes

Joined Oct 17, 2009
252
that's exactly it.

Now to make something.

Still, with an 556, how would you do it?

If you had the first timer, for the off period and then the second timer for the 20ms. you still have the problem of the first timer being on when it's supposed to be off. I think?
 

retched

Joined Dec 5, 2009
5,207
The first 555 would hit and reset. So it will pulse the second 555 then reset to its original state waiting for the next trigger.
 

Thread Starter

bluebrakes

Joined Oct 17, 2009
252
ok... i managed to find a circuit on the net that roughly did what i wanted it to do... and played about with it in multisim.

It seems to work great in simulation mode.

Does it look ok to everybody else?
 

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SgtWookie

Joined Jul 17, 2007
22,230
If you connect the low sides of C2 and C5 to Vcc instead of ground, that should keep the circuit from triggering when power is first applied. Then for C3 and C4, use 10nF.

Pay attention to cap polarity. If you move the cap, connect the + side to Vcc, and the other side to where the + was previously connected.

If you keep the low sides of C2 and C5 connected to ground, you'll need the large caps for C3 & C4.
 

Thread Starter

bluebrakes

Joined Oct 17, 2009
252
I've found a circuit, which has been tried and tested (on a few websites)...

Although I'm unsure which are supposed to be electrolytic capacitors.

I'm fairly sure 10uf is supposed to be electro cap. But I would have thought there would be two.
 

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Thread Starter

bluebrakes

Joined Oct 17, 2009
252
I built it tonight...

tested it on the oscilloscope and it seems to work a treat...

variable from 1 second to roughly to a 1ms. The truth will be when I come to try it out with the camera trigger. oh... and make it presentable in a box.

A few pics so far...

need to cut down the pot shaft, place in a module box and find a suitable knob.
 

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