Optical sensors with EduBot

[Lloyd Burns]

No, you are not going to be "crossing batteries". The collector of the output transistor in the sensor is not connected to the sensor supply. The highest voltage in the circuit due to the sensor supply is at the base connection, typically 0.6 V above the common ground on the EduBot.

Essentially, the transistor is only a path for current from the input to ground, exactly like a relay contact (neglecting the saturation voltage of the transistor, around 0.2 V, typically). The sensor o/p is "isolated" from the the sensor supply, and run in a saturated condition, usually.

My comment that the sensor might like more voltage is based on the printed voltage requirements on the side of the sensor - "10-30VDC". Often, when connecting to counter-controllers (like the Omron H7BR I have recently been fiddling with), the sensor is connected to the controller's power supply which can be selected to either 12V or 24 V (in the case of the H7's). The designer of the sensor probably had a certain voltage range in mind for the circuit, and there could even be a regulator in the package to make the sensitivity setting repeatable.

The sensor might work at 7.5 +/- 1.5V from the NiCd, but the lessons learned may not be applicable to the Full-sized Bot. A trivial test with the IR sensors ("xxxD" not xxx"LV") shows that at 6 V, the "white piece of paper" detection range for the setting it was left at, is 1/2 the range of the same sensor at 15 V.