On the bench today I tinker with a phototransistor circuit. I connect it to the oscilloscope and audio amplifier to see and hear the output. Let's see if an ordinary transistor is sensitive to light.
Yeah I always found it really interesting that any PN junction device can be used as a photodetector. This will work with LEDs or regular PN junction diodes. It's easiest to use a diode with a glass package like a zener or a 1N4148 signal diode. I can get almost 2v and maybe 25microamps out of a white LED as a photocell. This effect works in reverse, as well. If you run enough current through a diode or a photocell or even a solar cell, it'll emit light. Though the light emitted is in the infrared, but you can see this infrared easily enough with a digital camera. Any digital camera will pick up infrared light without any modifications to it. You can test this yourself by pointing a TV remote at your phone's camera and you can see the LED flickering when you press a button. It's really neat!
Could you control the gain reduction on the base of the phototransistor by, say, a 2.2K (fixed) + 5M (pot), to allow low/high gain as needed? Also, might be interesting if a jig was made with white LED (powered by DC) directly aligned at the phototransistor (with circuit as used), whereupon you try passing smoke/water vapor/?? or even the heat rising from a candle between them, to play with sensing "optical transmissivity"
Good lord, John, that's an old package. (sheepishly) I still have some old Archer packs in my kit. Almost makes me want to dig out the old Lafayette stereo and work on that. (Now there's a name from the past! ;) ) Keep the vids coming.
Great demonstration. A couple of things: first, perhaps it was not apparent during filming, but at 6:41, the LED bulb does appear to cast a flickering light, just barely visible at the top. Also, what are the two music tracks you used, out of curiosity? Thanks!
Is it possible of we make it reverse? For example once the phototransistor detect a dim light the led will light on. Because phototherapy lamp which is use for jaundice baby using photototransistor to detect a decreasing of light produced then a warning LED will light up.... so does anyone know how it can be happen?
reminds me of an episode of "Burn Notice", where michael bounces a laser off the large window of a room where people are speaking, uses the reflected beam to hear what they are saying. (so basically the reverse of what you're suggesting)
Would an incandescent lamp on a direct DC source flicker, like and old flashlight. It makes sense that a lamp on an AC source would flicker at 60Hz or 50Hz in Europe.
i was trying to do isolated current control on the +ve side with an n-mosfet, connecting the gate to a pull up resistor of 6.8k to 9v and collector of a pc817 to pull down the gate voltage ground. the led of the opto is being driven by an opamp (via a 330ohm) connected in diff amp config to a separate power source. but it's not working properly, when it's in action it's pulling down a lot, then doing sort of proper control to some range. i am thinking, this is because the opto interface is not as responsive. any suggestions please ?
Check rate of change at output of opamp and isolator through rate of change across the sensing device. Do this test separate from the circuit or the effects of feedback may mislead you. Once the circuit is working properly through its detection range, interface it with the mosfet gate. You may need to tinker with the gate circuit to get it regulating properly.
I went to the RS site and looked up "locations near me" and it returns "authorized dealers" and some come up as pharmacies and other non related businesses. I'll have to go to one and see what the hell is really going on. There is no "real" RS store within a 100 miles of me now. I thought several hundred were to remain in business.
