Infrared Trigger for Timer Module
I was experimenting with one of these Chinese timer modules like the one pictured to the left and needed an invisible and non contact way to trigger it. My thoughts went to using a matched pair of an infrared LED and photo-transistor so I looked around for a simple circuit but found nothing suitable. After some trial and error designing I came up with the circuit presented below.
The trigger circuit shown below is essentially an inverting amplifier. As long as Q1 is illuminated it conducts and pulls the base voltage going to Q2 to near ground potential. When either the LED or the transistor is shaded, Q2 is switched on and fires the optocoupler trigger inside the module. In practice Q2 can actually be located at the terminal strip on the module with only the base connection going to the outside world.
In my application D1 and Q1 are facing each other with less than a 4 inch gap between and it works great. Depending on what device you are triggering some lower value of R2 may be necessary to provide more drive to Q2. If high current is desired, say for driving a small relay, one could add another 2N2222 in a Darlington configuration but I found that unnecessary for the Chinese timers.
Side note: A lot of these modules are advertised on eBay at 6-30V input range. I smoked one with 19 volts even though the board itself says 6-20V on the underside. My 2 cents worth is keep the voltage below 15 on these things! FWIW: They are handy devices.
I hope you find this information useful. As usual I end by noting the fact that I am not an electrical engineer, just a hack tinkerer ham radio guy so take that into account when considering this design. If you damage your equipment or burn down the block trying to use something you find on this site, don't come crying to me. Heck, how do you think my junk box gets supplied? Enjoy!
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THE ABOVE CIRCUIT AND TECHNIQUE FOR TRIGGERING A TIMER MODULE SHOULD BE DONE AT YOUR OWN RISK. THE AUTHOR, THIS WEBSITE, NOR THE WEB HOST ASSUMES ANY RESPONSIBILITY FOR THE SAFETY OR ACCURACY OF THIS INFORMATION. THERE IS NO WARRANTY EITHER EXPRESSED OR IMPLIED THAT THIS METHOD AND PROCEDURE IS SAFE AND NO LIABILITY WILL BE BORNE BY ANY PARTY INVOLVED IN PREPARING OR PUBLISHING THIS DOCUMENT. CIRCUIT FAILURE MAY RESULT IN DAMAGE TO THE EQUIPMENT ON WHICH IT IS IMPLEMENTED AND OR PERSONAL INJURY MAY RESULT. THIS CIRCUIT AND SYSTEM SHOULD BE CONSIDERED EXPERIMENTAL AND IS OFFERED HERE FOR INFORMATIONAL PURPOSES ONLY.
USE AT YOUR OWN RISK!