Optical sensors with EduBot

Is there any good way to power a banner sensor/optical sensor with the EduBot? We could connect it in the same way that we would for the RC, but we are worried about whether the ground pin on the EDU-Rc could accept the 7.2 volts from the battery, instead of the 5 volts sent by the signal pin. The banner sensors work on 7.2 volts, but they do not work on 5 (6.6 is about the limit).

It’s buried in this thread.

The Banner sensors just use current sourcing, so it should be safe just to hook the Brown and Blue wires up to the battery as you would normally, and put the white wire to the EduRobot digital input (+).

The manual says the sensors need 10-30V DC to operate normally, so you might need to use 2 9V batteries connected in series for this to work.

Basically:

  1. Connect the (+) terminal of one 9V battery (Battery1) to the (-) of the other 9V battery (Battery2).
  2. Connect the Blue wire to the unused (+) terminal on Battery2.
  3. Connect the Brown wire to the unused (-) terminal on Battery1.
  4. Connect the white (or black) wire to the (+) on the EduRobot digital input.

The Banner sensors’ outputs merely take the input pin to ground. They might like more voltage than the EduBot battery has, in which case you could lash up some 9V batteries, and feed the sensor(s) approx 18 V.

*Originally posted by Lloyd Burns *
**The Banner sensors’ outputs merely take the input pin to ground. They might like more voltage than the EduBot battery has, in which case you could lash up some 9V batteries, and feed the sensor(s) approx 18 V. **

It’s considerably more complicated than that, but basically that’s what I said. If they did that, they would most surely damage the digital inputs.

The problem with this solution is that you are crossing batteries (feeding power from the 9V batteries into the NiCD battery). One pole will become depleted much faster than the other pole. Although this shouldn’t lead to any problems, it isn’t a very good practice.

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.