Compatibility of IR Sensor with Propeller

robotics

Hi,

In the Parallax Process Control Manual (page 117 - attached) a QRB1114 IR Sensor (spec sheet attached) was used in a 5V BS2 configuration. I would like to use the same sensor in a similar configuration in the Propeller Prof Development Board but I wasn't certain about the 5V to 3V compatibility. If (??) the anode and cathode of the IR LED can be connected to the +5V and -5V rails, and the 10K resistor and emitter of the photo-transistor can be connected to the +5V and -5V rails respectively as they are in the BS2, how can the correct value of the resistor (currently 220 ohm) leading into a Propeller IO port be calculated?

In advance, thank you.

Mike Green

I don't know why you're using +5V and -5V rails since both the LED and the phototransistor should work fine at +5V/0V and Vss is normally 0V. The LED resistor has to be higher or you'll burn out the LED. With +5V/-5V, the resistor would have to be 1K for a 10mA LED current. With +5V/0V, you'd need a 330 Ohm resistor for the LED. The phototransistor and the 10K resistor would work with either +5V/-5V or +5V/0V, but you'd need a 2.2K resistor between the phototransistor's collector and the Prop I/O pin when using +5V/-5V to protect the Prop against damage from the -5V. Using +5V/0V, you could keep the 220 Ohm resistor shown or leave it out if you wish since the 10K resistor will limit the current from +5V to the Propeller I/O pin.