Infrared LED and Phototransistor

[Felipebrz]

I have bought a couple of TIL32 (Emitter) and TIL78 (Phototransistor) for a project. However, when I ordered it the seller put the components each on different bags, but did not write which was which. Since they're all the same (they're both shaped like LEDs) I have not been able to determine them apart!
Can someone give me an idea on how to identify them?

Thanks!

 

[Diver300]

The Emitter will be a diode with a forward drop of about 1 V. When you put a few mA through it, the light should be visible on a cell phone camera or a video camera. Keep the supply voltage less than about 5 V and use limiting resistor of around 1 kΩ so that you won't damage things.

The phototransistor won't conduct at all in darkness.

 

[Felipebrz]

Thanks! I managed to find the emitter and its pins. The flat part (viewing the led from above) is tied to the ground and the round part to a 56\Ohm resistor, giving, at V=5V a current of 65mA. I tried with 1k\Ohm but got barely 2mA from the power supply. The voltage accross the TIL32 is about 1.4V. Neither it nor the resistor got too hot, but maybe i'll increse the series resistor.

As for the TIL78, do you have any idea how can I find out which pin is which on it? Its package is like a regular LED (just like the TIL32, thats why I had a hard time telling them apart).
And also how can I test it?

Thanks!!

 

[KeepItSimpleStupid]

Use the diode scale on your multimeter and illuminate the transistror with a source of IR even a tungsten lamp should do or you can use one of your emitters.

You will get a voltage drop on the diode scale of your meter if (-) is connected to E and + to C AND there is a source of IR.

 

[Felipebrz]

Thanks for the help KeepItSimpleStupid!
Since on my meter the diode scale is the same as the beeper scale, I managed to beep it when I got the emitter close to the receiver.
However, as I increased the distance, the meter stopped beeping, meaning that the receiver is no longer conducting, right?
I am using a small value resistor 56Ohm, if I decrease the series resistance, can I increase the distance between the emitter and the receiver?

Thanks!!

 

[KeepItSimpleStupid]

I am using a small value resistor 56Ohm, if I decrease the series resistance, can I increase the distance between the emitter and the receiver?

What series resistor, emitter or detector?

In any event, I would not use more than 50 mA on the emitter side. That would be R needs to be greater than (PS-1.2)/50e-3. PS is the power supply voltage. The DVM has built in current limiting so nothing is required there.

For your smoke detector, I believe you will need better sensitivity and you would have issues with aging and regulating the emitter current and measuring the detector current.

You can shorten K...d to KISS.

The diode scale of your meter is good for identifying, but it doesn't quantify.

 

[podoljanko]

your phone camera, or webcam often shows infra red light as a white glare, you can test it with a remote control. thats atleast ana easy way to find the ir led

 

[Felipebrz]

Thanks everyone!
To test the distance and alignment of the emitter and receptor, I made a simple circuit with a regular green led in series with a resistor tied to +5V and the colector of the infrared receptor. The emitter was grounded. Whenever I got the emitter and the receptor aligned, the green led would light up and the brightness of the led would mean how well aligned it was. Very nice!!
Since this arrangement is mobile, I'll add this green led in the final circuit, just to make it easy for the user to align the pair of infrared devices. I'll also add a 10k pull-up resistor so whenever something block the infrared beam, it'll trigger something in a microcontroller (by giving it a 0V level hopefully)