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I'm sure there is someone out there who has used a servo to trigger a digital camera, I am getting a bit confused which technique to go with. I have a Dynam 8.4g servo that I would like to trigger whenever a Normally Open contact goes Normally Closed and will stay triggered until it goes Normally Open again, that way can swap in a cable remote, interval timer or radio trigger for whatever situation I am in at the time.

Glenn

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Im not sure what the question is but if you want ways to drive a servo there are many on the net using pic controllers or 555 timers.

Terry

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I've put together a few 555 circuits that I found on the net, none of them will move the servo, maybe the ones that I came across were fakes!

Will a 555 reset the servo to center when the trigger is removed?

Glenn

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You can make the servo go to any position by changing the resitors, the easy way is to switch between preset resistors.

Terry

Edited by Terry

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I hope I got the formulas correct for R1, R2, C1, C2

I based 90 degrees rotation at the servo on a frequency of 100hz at pin 3

I'm not sure what value to put at R3 yet as I don't know if I have to go up or down in frequency.

Do you think this circuit and component values will work? I can't test it yet ( out of 3K9 resistors)

Glenn

555TriggerCircuit01.bmp

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The circuit will not work correctly. You need a fixed frequency (frame period) that is approx 50Hz (20mS) and servo movement requires a pulse width (the actual servo pulse) variation that ranges between 1mS and 2mS. So search a bit more for circuit designed to drive R/C servos. There's a lot of them published out there.

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I found a reference on the net to aim for 100Hz, another false posting by the look of it, back to the formulas.

Other than the wrong values, am I on the right path or is having the trigger fire close contact with R2 incorrect technique?

Glenn

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best to just build it and play with the values a bit to get what you want.

Terry

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I found a reference on the net to aim for 100Hz, another false posting by the look of it, back to the formulas.

Some servos will accept a 100Hz frame rate, but not all. So it is best to stick with 50Hz. But there is more to it than just the frame rate frequency. An R/C servo is moved by changing the width of the pulse, not the frequency. That is why R/C servo control it is called PWM (pulse width modulation).

As mentioned, there are existing servo control circuits published on the net, including the R/C servo tester published on this site. Just pick the one that uses the components you are most comfortable with. One example of a LM555 servo PWM driver was found by Google:

http://www.princeton...002/292-302.pdf

http://www.sentex.net/~mec1995/gadgets/servo2.htm

And more examples here: http://www.sentex.ne...ets/gadgets.htm

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My mistake going working on frequency not Pulse width, more study needed, thanks for the links

Glenn

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