Mystery component help

Pyrotom

I'm working on a Prop based project which needs to sense flow of liquid in a pipe, so I was thrilled to find the "Unknown Flow Sensor" at All Electronics for a very reasonable price. The only problem I have is that "Unknown" bit.

I'm pretty good at programming, but not so hot on electronics, so I need a little help! I've attached a picture of the LED and what I assume is a phototransistor that are used in the flow sensor to watch a little paddle wheel turn. The LED is no problem, I can figure it out by trial and error. But how do I figure out what is what with the phototransistor (probably NPN, if my web research is correct), and can someone suggest a circuit to connect it to a Prop I/O pin so that I can read it? Thanks!!

Post Edited (Pyrotom) : 6/11/2008 7:43:25 PM GMT

Leon

Try connecting the collector to Vcc though a 1k resistor and ground the emitter. Put a DVM between the collector and ground and shine IR at the active area. You should see the device working when you interrupt the IR.

Leon

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Pyrotom

Thanks! How do I tell which is the emitter and which is the collector??

Leon

If you don't have the data sheet you can use a DVM to find the base out of the three leads using the diode setting. Then measure the forward-biased resistance between the base and the other two leads; the one with the lowest resistance is generally the collector, the junction is larger as it has to dissipate more power than the emitter-base junction. Practise with a transistor with a known pinout first.

None of the photo-transistors I've used have had a base lead, the light causes current to flow in the same way as current injected at the base. It is possible to use the base connection to adjust the sensitivity of the device, but I wouldn't bother with it.

Leon

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Post Edited (Leon) : 6/11/2008 9:41:23 PM GMT

Phil Pilgrim (PhiPi)

My money would be on it not being a phototransistor, but rather a Schmitt-triggered digital-output (open-collector or totem-pole) photodetector. The third pin is the tipoff, and the TO-92 form factor is common for these kinds of devices. Here is a similar device from Optek. I have no idea, though, if pinouts for these devices are common across the board.

-Phil

Pyrotom

Looks like you win the bet Phil! I breadboarded it up as described for the OPL550, and once I got the polarity right on the LED it works like a champ. Thanks so much for your help!