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- Size: 42 x 19 mm
- Weight: 19 g
- D-shaped shaft hole of 3 mm diameter
- Rim colour: white
- Supply voltage: 4.5 V to 5.5 V*
- Power consumption: 14 mA for 5 V
- Two digital outputs (quadrature)
- Small size 18
- Weight 1,6 g
* It is also possible to supply 3.3 volts through a suitable calibration.
- Two wheels with tires
- White extension mountings for Polyol micromotors
- Optical encoder set for speed measurement
The quadrature optical encoders, designed for Polol's micro motors, consist of two infrared reflective transoptors. The measurement is carried out by reading the current position of the sensor using teeth and slots in the wheel rim. The output signals are shifted inphase by about 90 degrees. This makes it possible to distinguish the direction of rotation. The outputs are connected via comparators with hysteresis, so that the signal is free of interference. The resolution of the encoders is 48 pulses per revolution.
The small size allows the sensors to be mounted between the motor and the chassis by means of extended mountings.
An example of a sensor operating code for AVR microcontrollers can be found in the Polol AVR library at: link.
Encoder wheels work with Polol micro motors with gears from 5:1 to 298:1. Sensors do not support motors with 1000:1 gear.
Calibration for 3.3V
The sensors can be set for operation with a 3.3V supply voltage. For this purpose, a R4 resistor should be bridged (shown in the diagram below). In practice, this means solder a piece of wire between two pads of R4 resistor, or remove this resistor completely and replace it with a jumper. This operation will reduce the total resistance in the circuit of the IR sensors' transmitting diodes. Only the R1 resistor of 100 Ω value remains (plus the resistance of the diodes themselves).
Diagram of the Polol optical encoder module.
The next step is to calibrate the sensors. For this purpose, use small potentiometers located on the board. Correctly calibrating the encoders should send out a signal with a fill of about 50%. Calibration is facilitated by the use of an oscilloscope, but this can also be done with the microcontroller itself by measuring the signal fill.
Thanks to their large treads, the wheels are resistant to bumps and dirt on the surface on which they move. The wheels are designed to fit the micro motor shafts of Polol.
The diameter of the tyre is 42 mm and its width is 19 mm. Rim dimensions are shown in the figure below.