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How to Make LED/LDR Opto Coupler

How to Make LED/LDR Opto Coupler

My good friend Mr. Chiverton shared his experience regarding the features of an LDR in comparison to phto-transistors for making opto couplers. Let's learn what he discovered regarding opto couplers during his experience with my ghost detector circuit.

Discussing the use of Optocoupler using LDR/LED

So far i've only done indoor testing and the ghost detector circuit responds like as if there is some residual static charge build up on some things around here in the house we live in but then for a charge build up there has to be an opposite charge somewhere for another object to gain the opposing charge .

makes me wonder if these so called orbs that we cannot see actually leave any static traces to or other thing Ive yet to do more tests and take notes which ill forward to you if using the trigger coil tester as a relay status, indicator remove any diode across the relay inputs, otherwise only one of the leds in the trigger coil tester modified as a relay input status indicator will blink .

the diodes and circuit of the trigger coil tester may resume the role as a diode in itself if it dose. also the end of the trigger coil not connected acts as an rf transmitter short range which can be picked up by the ghost detector circuit just thought id let ya know .

also photo transistors the 3 leg types no longer on sale at any electronics stores here but there is a 2 leg photo transistor but infrared type only so ill latter update the ghost detector to use the photo interrupt which sell still , as my last few fair child photo transistors will soon be used up for making the home made optocoupler circuit for the ghost detector.

Hi Steven,

That was a good discovery, I will put the whole thing out there.

Thanks and keep up the good work,

looking forward to hear more from you.

this is an upgraded 6 million gain circuit using the swagatam buzzer circuitry, unfortunately my last 2 rare fairchild photo transistors didn't work so i put in this metal body photo cell with built in lens and it works but very sensitive at detecting static charges to, like the first 6 million gain circuit , which the led on it responds to static charges up to 11 feet away minimum so that's very sensitive ,

in fact its sensitivity beats the ridiculously sensitive charge detector circuit by a mile , as i also built it to and tested it so even though all the ghosts detectors also sense static charges to they also still ok at sensing ac fields and most sense the body e fields or energy fields or the aura as this 6 million gain circuit dose it well especially when you move your fingers when holding the box its housed in after letting your energy warm the box for a bit

Hi Steven,Thanks,

when it comes to sensing light (as in our opto-coupler) I think LDRs are more efficient. Moreover they are easy to handle and much cheaper.

I have a good and long experience with LDRs and found their working to be wonderfully well.

Thank you swagatam

ive just finished testing all my ldrs even the large on on the buzzer circuit built separate and not one of them works for me , strange considering ive never used these ldrs yet not for years and

when i measure them on my multimeter they register as 1k in the dark state and when i put light to then the resistance jumps to above 6k and if i use them in the separate buzzer circuit, the buzzer sounds loud with light shining on the ldr and also sounds loud still when they are dark.

at least 3 of my ldrs make the buzzer sound alter only slightly when i move light to it and away but thus still sounds loud and never silent even loud when i cover the ldr to block out all light

Hi Steven,

I don't quite agree with you.

There's definitely something's wrong either with yours LDRs or the procedures. I have used LDRs in many of my projects - these devices are WONDERFUL.

Please do the following steps to check the LDR response:

  • Take the LDR, connect the multimeter prods to its legs, and hold it firmly with your fingers. Let the ambient light fall over the LDR.
  • The meter will obviously show certain low value. Now shift the "face" of the LDR somewhere towards the darker side. You should immediately see a change in the reading of the meter (increased resistance).
  • Make the LDR face different light intensities by manually shifting its direction. The meter should display different corresponding readings (resistance values).
  • This will convincingly prove the correct working of the LDR. Also, at complete darkness the LDR should show INFINITE resistance.
  • If these conditions are not met, then definitely your LDR is a faulty one.
  • Once the above correct functions of the LDR is confirmed, now you may configure it to the opto coupler. Also remember the opto coupler should be housed inside a PERFECTLY LIGHT PROOF ENCLOSURE, otherwise it will behave erratically and produce wrong results.

Thanks swagatam

ill retest the ldrs again let you know. what are the chances of all of my ldrs being faulty even though i haven't used them all up in all the years ive had them they've been sitting in my parts drws for so long il get back to you ill also test the transistor for the buzzer circuit and see if that's ok to your right swagatam

i underestimated the ldrs super sensitivity. first i blocked all light from it using my fingers, in a room that has some light in it and tonight i did a better test with the window blinds closed and less light

so i was in darkness and the buzzer circuit which i ran the ldrs to was ok transistor tested ok and the buzzer in the dark died down to nil in the dark so they wasn't faulty after all but the only failure i got was my largest cd photocell or ldr in the dark the buzzer was still sounding and

when i applied light to it it got louder also using my finger to block light wasn't so useful after all as even the light at its lowest still went through my fingers and the high sensitivity of the ldr made it easy detectable

still so the light has to be blocked much more from entering the ldr , especially through my glass fingers , i have some info i collected some time ago scientists saying that parts of the hand emit light even though we cant see it do you think its the case to of using a finger to block light when it emits invisible light and the ldr still senses it to with your finger covering the ldr.

Hi Steven,

  • Thanks - The theory behind the emission of photons by human hands might be true, in fact all living beings emit photons to some levels, but are too low to practically detect.
  • The level of LDRs response to light is quite equal to our eyes. It simply means that any light that is not visible to our eyes cannot be "visible" to the LDR.
  • As we know it is almost immpossible to contain light, water and air in our hand, therefore in your experiment, its only the ambient light which is passing through your hands and not because of anything that is being emitted from your hands.
  • The opto-coupler needs to be SEALED inside an OPAQUE enclosure to produce the optimum results.

About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

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