5Pcs Speed Measuring Sensor LM393 Speed Measuring Module Tacho Sensor Slot Type IR Optocoupler for MCU RPI Arduino DIY Kit with Encoders

All tested ok, quite a bonus to have the dupont wires as well, especially for this price.

Good value and performed as expected. The only issues that I had were more to do with how I was using them, rather than any special device defect. However, I will explain here in case it helps others.1. I needed to fit these face down on the chassis of a cheap robot car kit. Unfortunately the connector pins, though angled outward, still protruded to much from the top of the board. Simple fix, I removed the connector and soldered wires directly to the board. I chose not to refit the connector on the other side of the board to improve robustness against vibration.2. I found that the sensors were occasionally seeing more slots than had actually passed by. Close examination with an oscilloscope revealed that, although at first glance the output pulses were nice and square, as I zoomed in I saw a small amount of noise on the leading edge of the output pulse. My work-around was to fit a 100nF disc ceramic capacitor between the output pin and ground (which although it reduced the sharpness of the square wave, also integrated the noise and leading edge in to a smooth(ish) slope).

These devices might produce a clean signal at high speeds as they are, but to get clean signals at low speeds the comparator needs to have hysteresis, which is lacking in this design. Fortunately it can be added by adding a resistor between the output and +input pf the LM393. This is what we advise our customers to do when they use these devices to produce pulses to feed into our electronics.

Pack recieved only contained two encoder discs. Product photo shows five discs, one for each sensor. This is clearly a quality issue at source.

The sensor does not produce accurate readings. It requires an external circuit to filter out the junk pulses.

One encoder disc was missing. The sensors, discs and ribbon cable are supplied in a thin resealable bag, which had split from the sharp edges of the ribbon connectors. So there’s a hole in the bag, that’s why things are getting lost.Both the Power and Beam LEDs are green, which is fairly dumb. Can’t tell from any distance what state it’s in. May as well not have bothered with the Beam LED at all.Other than that, they boards work great.