CRT5000 sensor work with an Infrared LED (950nm) and a photo-electric transistor. The whole things included within a box allowing the light to get inside.
This sensor is used to detect contrast changes on the surface. A white surface reflect a lot (infrared) light to the photo-electric sensor (which activates the transistor). On the other hand, a dark/opaque surface return very few of the infrared light and the photo-electric sensor is not activated.
We can use this type of sensor for:
- To detect shaft rotation (with an encoder)
- To detect white line on black background.
- To detect reflective material (like white cardboard, paper, magnetic strip, CD, ...)
- To act like a switch to limit mecanical movement (used a lot in older tape reader)
- Where there is really few room to place a sensor.
Measure distance from 3 to 6mm.
The first time we meet this sensor was in a gaz counter decoder. As the white digits have different shape, the quantity of light reflected to the photo-electric sensor will vary from digit to digit. For each digit, the reflectance scheme will be different. It is possible to detect the 9th digit (so when the counter did make a complete turn :-) ).
To make this sensor really efficient, it is very important to have surfaces with different reflectifve factor (significant difference). By example, black mate vs white mate. The black mate have a reflectance ratio from 0 to 10% whereas the white mate has a reflectance ratio from 90 to 100%
The datasheet mention an optimal current of 20 mA for the infrared LED (and also a current of 40mA). For long term usage, you should use a 20mA to avoid degradation the LED.
On the other hand, higher is the current, higher is the infrared illumination, higher illumination improves the efficiency of detection.
For a 40mA current, you will use a 125 Ohms resistor (for a 5V power supply).
Using a 250 Ohms resistor will limit the current to 20mA (also for a 5V power supply).
Two ways of using it
- By using a resistor, you will ba able to read the voltage with an Arduino's Analog Input... you will have to analyse the input signal to detect when it activate
- You can also use a operational-amp with a potentiometer to assign a trigger signal. This will help to transform the analog input signal to a digital output (high / low level)
- Sensor type: Phototransistor
- Dimensions: Length 10.2 mm x Wide 5.8 mm x Height 7.0 mm
- Optimal working distance: 2.5 mm
- Working distance: 0.2 mm to 15 mm (it is recommended to stay under 6mm)
- Testing condition: typical current: Ic = 1 mA
- Filter the visible light
- Wave length of IR LED: 950 nm
- TCRT5000L technical detail
- You will find lot of ressources on Internet.
This sensor is very appreciated by makers because it is easy to use.