TheMutt 0 Posted December 16, 2010 Report Share Posted December 16, 2010 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 Quote Link to post Share on other sites
Terry 5 Posted December 16, 2010 Report Share Posted December 16, 2010 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 Quote Link to post Share on other sites
TheMutt 0 Posted December 17, 2010 Author Report Share Posted December 17, 2010 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 Quote Link to post Share on other sites
Terry 5 Posted December 17, 2010 Report Share Posted December 17, 2010 (edited) You can make the servo go to any position by changing the resitors, the easy way is to switch between preset resistors. Terry Edited December 17, 2010 by Terry Quote Link to post Share on other sites
TheMutt 0 Posted December 17, 2010 Author Report Share Posted December 17, 2010 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 Quote Link to post Share on other sites
Mr.RC-Cam 129 Posted December 17, 2010 Report Share Posted December 17, 2010 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. Quote Link to post Share on other sites
TheMutt 0 Posted December 17, 2010 Author Report Share Posted December 17, 2010 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 Quote Link to post Share on other sites
Terry 5 Posted December 17, 2010 Report Share Posted December 17, 2010 best to just build it and play with the values a bit to get what you want. Terry Quote Link to post Share on other sites
Mr.RC-Cam 129 Posted December 17, 2010 Report Share Posted December 17, 2010 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 Quote Link to post Share on other sites
TheMutt 0 Posted December 17, 2010 Author Report Share Posted December 17, 2010 My mistake going working on frequency not Pulse width, more study needed, thanks for the links Glenn Quote Link to post Share on other sites
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