I mounted first 25 pcs of rotating speed sensors. It has 2 IR LEDs lightening the rotating surface and photoelement connected with operational amplifier working in comparator circuit. The op-amp compare actual light level with moving average. In that way it can adapt itself to wide range of lighting conditions.
Sensor can works with own source of the light, for example lightning black and white sticker on electric outruner engine or with existing ambient light looking on it through propeler. In case of work with own reflected light the distance between sensor and rotating element should be not bigger then 5cm. In factory settings all optical components are set paralelly to each other. The LEDs emit a beam with an angle of aperture 50°. Photo element collects th light from the angle 24°
The LEDs and photo element are soldered to have 2mm distance above board's surface. It allow to some degree of modification in case on not typical conditions. If we want to decrease sensor height, we can resolder LEDs and move it more close to board. Also backside wires can be cut to keep minimal lenght.
In situations when size of the sensor is critical we can cut the upper part of the board with second mounting hole. Simply break the board on the line marked with 4 small drillings. The upper part has no electrical connections, it is only for mechanical purposes. Cables to sensor has to be threaded via holes nex to soldering pads and next soldered. That way of mounting protects wires from breaking.
Sensor has 3 wire connector. Pads are described as "+", "out" and "-". Pads "+" and "-" should be connected to 5V power supply. On the pad described as "out" will apear electrical signal with frequency proportional to changes of reflected light.
In case of working condition when sensor has to works with very small distance to reflecting surface the LEDs should be bend close to photo element to light directly ahead it. Because LEDs works in not visible range of infra red light, the helpfull tool can be simple camera without IR filter, for example camera in cellphone. Using it we can see LEDs lighting and control location of the hot spoots on the working surface.
Conecting sensor to any measureing systems please remember the propeller produce frequency multiplied by number of blades. Analogical situation is with multiple stickers.
The sensor can be bought in Pit.Lab.Shop