parts:
R1 270 ohm resistor
R2 10k resistor
LED1 Infrared LED
Q1 Infrared-sensitive photoresistor


This is a very basic infrared detector/emitter circuit. One major downside of this circuit, is that ambient infrared light will interfere with its detecting obstacles.

I have this diagram, from Robot Builder's Bonaza, but how do you hook it up to a comparator, i thought i figured it out from the previous pages in the book, but my circuit doesn't seem to work. And also, which lead on a phototransistor is the collector, the shorter or the longer one, i may have hooked up the phototransistor wrong and damaged it... please help.

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by the looks of the schematic, the led and phototransistor/resistor should have similar packaging. if that's true, then the lenghts of the pins should be the same as the led.

on led's usually the flat side of the package marks the cathode (band side of the schematic symbol) and that should be the shorter negative side.

the longer pin should be the positive anode side.

unfortunately this isn't a standard and might be inconsistent.. but it should work most of the time.

As far as using this circuit.. the will be dependent on the amount of IR hitting the phototransistor. I don't know if the output will be proportional to the amount of IR being detected, or inversely proportional. It probably depends on the type of phototransistor. But to get results, you'll need to hook it up to a device that turns on above a voltage, and off below that voltage. Usually you can use resistors to set the on/off trigger point. You will probably want to use a voltage meter to get readings when you're building this circuit.

hope this helps.
-andrew

Thanks for your help. One more thing, could I have damaged the phototransistor by hooking it up with the pins in the wrong position?

could have? sure.

I'm sure it's fine though.. you can use the voltmeter to check.

-Andrew

You have to much time on your hands........

Quote

(Guest @ Jan. 14 2004,23:12):
Thanks for your help. One more thing, could I have damaged the phototransistor by hooking it up with the pins in the wrong position?

You can use a meter (analog or digital) to check the diode. Forward biased it should show about .7-1.5 volts voltage drop in diode check... reversed bias should show no drop or infinity resistance.

The phototransistor is a little trickier, but can be checked the same way.. put your meter across it and supply a IR source to turn it on. (sunlight, your LED.. ... a remote control... etc)

Good luck!

Quote

(Guest @ Jan. 09 2004,23:39):
And also, which lead on a phototransistor is the collector, the shorter or the longer one, i may have hooked up the phototransistor wrong and damaged it... please help.

Collector-short leg
Emitter-Long leg
it will onlt be damaged if the voltage was high enough.


btw
how do hook this circuit up to motors? is this circuit good for line tracking?

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mailto:kiri_kara2000@yahoo.fr

i wante to have a schematic of practical PASSIVE INFRARED DETECTOR (used in alarm systeme).My question is :
it is possible to NC contact to supply an 12V-dc relay
Thanks very much.................

mailto:kiri_kara2000@yahoo.fr

i wante to have a schematic of practical PASSIVE INFRARED DETECTOR (used in alarm systeme).My question is :
it is possible to use NC contact to supply an 12V-dc relay
Thanks very much.................

Quote

(andrew @ June 26 2003,21:59):
One major downside of this circuit, is that ambient infrared light will interfere with its detecting obstacles.

Not if you set each one in a shallow tube (about 1 inch)

smart move with the tube thing. it also makes for a good field housing.

the focus of the beam can be changed by varying the bubes length too ( or the item's depth in the tube)

how do you use this circuit with motors-when object is detected?

Try using a relay
, and put it in series with the LED

ummm, the voltage might be a bit too low for relays tho

Something like this would work better
the 2N2222A gives you enough power to triger most relays and the relay alows you to use even more power

can yu show me an IR emmiter/detector cct that can sense within upto a 1m range.i want to use it for an intruder alarm design,
URGENT.

andrew Wrote:
-------------------------------------------------------
> [www.reconnsworld.com]
> etectemit.gif
>
> parts:
> R1 270 ohm resistor
> R2 10k resistor
> LED1 Infrared LED
> Q1 Infrared-sensitive photoresistor
>
>
> This is a very basic infrared detector/emitter
> circuit. One major downside of this circuit, is
> that ambient infrared light will interfere with
> its detecting obstacles.

Hi, I want to data log the IR pulse on my domestic electricity meter.

Can I use the detector side of of the above circuit posted by andrew to sense the pulse or is there a better circuit for this application?

The pulse signal will be counted by a Dallas 1-Wire counter.

Many thanks for your help.