New line sensor

I had some problems with the 36 KHz detector when trying to read it from the picaxe, so I have switched to using 4 infrared photodiodes in a feedback setup with two LM358 dual opamp packages as shown in the following image (for one photodiode only):


This gives an analog reading and I will use this for linear interpolation between the sensors to determine where the line is relative to the robot center.

Could you elaborate a bit?

Your schematic only shows 2 units send/detect… Could i get a little more? maybe some part numbers for what you are using?.. More please baby!!

Hi Chris,The schematic

Hi Chris,

The schematic actually shows just one infrared light sensor (of which I use 4 in my line sensor thingie). At the far right of the schematic you can see that it is to be connected to a PICAXE analogue input pin.

First of all I have discarded the voltage divider with the variable resistor seen in the top left of the schematic (and connected to pin 3 of the LM358). From now on I just connect pin 3 to ground.

The diode, D, is a PD638 photodiode which does the actual light reception. The LM358 is a dual operational amplifier (and I use two of these since I have 4 sensors).

Below the LM358 are a capacitor and a resistor. The resistor is creating a feedback from the amplifiers output to its input. If it wasn’t there the output would be 5V all the time. The capacitor is there to stabilize the output. The resistor is 1M and the capacitor is 47 nF as far as I remember.

Hope that was a little more helpful?

- Jimmy