Useful Rotary Mouse Encoder

An extract from RMP meter Project;

"We decided to try and recycle a simple ball mouse into a useful encoder for our project. Each mouse has at least 2 rotary encoders so we attempted to reuse these encoders into something that can be used with a microcontroller for an input device as a rotary pulse generator (RPG). Useful !!
After examining several types of mice, we found there was quite a range of technology used in the detector circuits. Some older mice used LEDs and phototransistors but the best units we found had an integrated detector that directly output TTL level quad rate signals. These units had 3 pin clear plastic IR LED sources and black plastic 4 pin detectors.

To interface to a microcontroller, all that was needed was one output pin to pulse the infrared emitter and two inputs to read the 2 phases of the encoder. The LED sources are pulsed on by the controller about 120 times per second (14.8µs on, 8.5ms off). When motion of the encoder wheels is detected, the pulse rate increases up to over 5000 times/second (14.8µs on, 172µs off). This operation results in three benefits. The LED life is improved, the current consumption of the mouse is minimized when it is not being used and the signal to noise ratio on the detectors is improved because the LED sources can be driven harder when using an 8.6% duty cycle.

Amazing Features of Mouse Encoder
  1. Low cost rotary pulse generator
  2. Resolution of around 256 pulses/revolution
  3. Pulse rates of up to several hundred pulses/second"

Posted by Muhammad Ahmed on 16:51. Filed under , . You can follow any responses to this entry through the RSS 2.0. Feel free to leave a response


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