Interesting quirk of p621 opticoupler if anyone interested

well i have a very small batch of p621 opticouplers that exhibit unusual characteristics perhaps it normal for these couples perhaps not. Is anyone else using couplers and do they exhibit the same characteristics for them …???

i was building a simple arduino circuit to drive some LED solar lighting project, that suppose to light up a local monument. and to save on power slowly dim the lights as time progressed . but anyways these opticouples are working as a simple touch sensitivity circuit - if what ever metal you have the single sensor wire connected to is under 1 square foot in surface area it will not drive the circuit . and also curiously it is also light sensitive. but it seams only to natural light . if I place in under strong led light nothing happen place it in a window the circuit closes and light comes on.

if these opticoplers work normally like this then it is fairly easy to build touch sensitive switches and alarms, plus other environmental switches if any one is curious…

Is that really only an opto-coupler? So you are saying that it is sensitive to ambient light? It is supposed to work on infra-red so if you are using a very high value of load resistor, there might be enough IR in daylight to get through the plastic package and make the detector conduct.
I think I’d like to know what your circuit diagram looks like and the values of the components.

Regarding the touch-sensitive part, I think it is much more likely that with the opto-coupler dark, therefore the output transistor is off, then you are seeing pickup by your Arduino’s very high impedance input, and it has very little to do with the opto-coupler. You could prove this by removing the opto-coupler but leaving all the other wiring in place. Then if you still see the same effect, it is not the opto-coupler.

if you look there is no arduino involved. it just the opticoupler p621 and irf9540n that I was going to use to open and close the circuit for the led strip . the other thing is just power supply for the rails at 3 or 5 volt on the breadboard but okay i tried a couple other type of lights - the coupler is seeing infared if i plug in a infared light in the room the circuit completes a UV nothing nothing happens …


to me it seams that the body becomes an antenna or any object over 1 square foot. which then captures enough RF from the power supply to drive the P621 - which either case is pretty cool effect :slight_smile: and simple switch for various touch sensitive applications

for the heck. here it interacting with an inferred light. which makes it a interesting low sensitivity inferred light switch . as it signal strength is about the same a solar panels light sensitivity to produce power . an normal house lighting does not effect it . but an infarred light does affect it even when it meters away - now i am very curious if it just my batch of p621 or do all p621 react the same

hey Robert you were some right on the touch sensitivity was not only in the opticopluar . it was also my irf9540n that was ultra sensitive. both would fire i tried other components differing fets and opticouples they did not do the same thing. though i could fire those non working FETS with the p621 i also. verified it was RF that was driving it. if I use an AC wall adaptor of any form it would work, use a battery to power it - nada. - nothing - but Rf also explains why a 1 foot square antenna would not drive it but 2 foot square antenna would. another interesting thing it seams it can be driven by the entire electrical field of the house as you can shield the circuit and the adaptor but you can still trigger by touching the single lead from anywhere within the building - which would make an interesting alarm or sensor system as not only human touch could trigger it but moisture, smoke