This T-Slot Photo Interrupter with Cable is a simple plastic sensor with two elements - an IR LED and an IR photo-transistor, situated across a U-shaped gap. You can control the IR LED and turn it on to transmit IR light across the gap, to the detector on the other side. This makes it perfect for detecting when something is in the slot. When there's something blocking the light, the sensor turns off, when the object goes away, the sensor receives the IR light and turns on.

These sensors are handy when you want to detect if something has passed through the sensor slot, we think it's great when paired with our slotted encoder wheels - as you can see we have a demo that will count the number of transitions (slots) over a second, extrapolate that to RPM, and display on an OLED. This sensor is extra fancy with a red LED on the side to let you know when the sensor is triggered, and built in protection circuitry.

We will mention the one down-side to this sensor is that the circuitry inside has power requirements - the Vin line must be powered by at least 5V. But, the output transistor is open-collector so you can connect a pullup resistor to 3V for 3.3v logic if you need. So, as long as you have some 5V power output, you can use it with a 3V device like the Feather shown in the demo.

This version is very fancy with a cable attached:

• Brown wire - VCC (logic circuit power 5-24V)
• Pink wire - L (LED configuration, see datasheet for options but we just tie to VCC)
• Black wire - transistor output. Open collector so you must connect a pullup resistor to your logic level.
• Blue wire - Ground