Hi everyone, i am a complete newbie to arduino and am trying to get a signal from an Infra-Red Finger / Ear lobe Clip Sensor part number EP-107 (from http://www.cosycommunications.com/Digit … alogue.htm )
without the use of an op Amp. I have wired the sensor up in the same way as the Arduino Potentiometer sketch but so far have just had a random reading. The ultimate goal is to turn servos with the output data. Any tips or hints would be greatly appreciated. Thanks 
You need an amplifier.
Leon
Hi Leon, thanks for your advice, do you have any suggestions as to which type of amplifier to use in order to get a readable signal and in which way it should be configured. I really appreciate your help. Thank you.
I’d use an op amp. You’ll find how to design the circuit in a good text book.
Leon
Thanks for your help Leon.
Although an amplifier would help, I’m not convinced that one is necessary. Looking at the link that was provided, this appears to be a simple IR transmitter/phototransistor pair. It is similar to devices like this [IR sensor. Tie the collector to +5v through a resistor and connect it to an analog input in the Arduino and see what readings you get.](http://www.sparkfun.com/commerce/product_info.php?products_id=8906)
The fluctuations in IR transmission resulting from the pulsation of blood in the capillaries are small, and quite a lot of amplification is required (something like x100).
Leon
Hi, thank you for your replies. I will try out your suggestion Ralph. Would the resistor need to be about 1 mega ohm? I also agree that the signal could be quite small, but will do this test first and fingers crossed it will yield a result. Thanks again.
It’ll be a waste of time, without amplification. You will probably also need a low-pass filter.
Leon
I think a 1 megohm would be a good value. You may be surprised at the voltage swing that you will get. I’ve used similar IR emiter/detectors in robotics applications and was pleased with the results. Of course, this is a different application, but I’m optimistic none-the-less. If you have a voltmeter, you could measure the change of voltage before connecting it to the Arduino. That will make diagnosing problems easier.
If you end up needing an amplifier, you might find [this project interesting. However, your probe looks like it has only three connections (GND, LED emitter, and phototransistor out). If you don’t have a schematic for your probe, I’d use a current limiting resistor on the emitter end to avoid damaging the LED.](http://www.bioe.psu.edu/seniordesign/SD2006/DFord/bioe450%20web%20page.htm)