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A more stable Arduino-based turntable tachometer

This respository contains all required files for the IR-sensor-based turntable tachometer.

Breadboard

Why reinvent the wheel?

Existing Arduino tachometer code that is flowing around the internet give erratic readings even when the IR sensor is properly debounced. They are not useful for speed sensitive devices like a turntable.

The code in this repository introduces a few improvements:

  1. Intantaneous speed readings are saved to a circular array. After the IR sensor collects the tenth reading, the average reading flag toggles and an average speed parameter is displayed on the LCD screen.
  2. Display response speed and memory usage are improved as the next reading will overwrite the earliest reading stored in the circular array.
  3. The timer interrupt routine handles the calculations periodically. The loop only performs LCD display tasks.

Required hardware and electrical components

  • Arduino ATMega328 based controller - I am using Arduino Duemilanove
  • Nokia 5110 LCD display
  • Custom IR module - see schematics below for more details
  • 5V to 3V Level-shifter for LCD display (I am using two 74VHCU04s)

The code is written for ATMega328-based Arduinos in mind. Slight modifications are required before compiling the source code for other Arduinos.

Custom IR module

Schematic The parts are choosen as they are what I have at home. The dual opamp NJM4560 serves as a LED driver and comparator for the Omron EE-SF5 IR sensor. You can also use one of those pre-built Chinese IR-modules instead and I recommend that in retrospect.

Best sensor response is achieved when the EE-SF5 sensor is mounted five millimeters away from the target. Check the manufacturer datasheet when using alternative IR sensors.