https://github.com/samie/tacho

Python script to drive a tachometer on Raspberry Pi GPIO using PWM. Show CPU, network traffic, or MQTT data.
https://github.com/samie/tacho

mqtt python raspberry-pi tachometer

Last synced: 21 days ago
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Python script to drive a tachometer on Raspberry Pi GPIO using PWM. Show CPU, network traffic, or MQTT data.

• Host: GitHub
• URL: https://github.com/samie/tacho
• Owner: samie
• License: apache-2.0
• Created: 2015-01-14T07:23:27.000Z (almost 10 years ago)
• Default Branch: master
• Last Pushed: 2015-02-17T17:18:08.000Z (over 9 years ago)
• Last Synced: 2023-03-14T09:15:30.625Z (over 1 year ago)
• Topics: mqtt, python, raspberry-pi, tachometer
• Language: Python
• Homepage:
• Size: 262 KB
• Stars: 4
• Watchers: 2
• Forks: 2
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# Tacho

Python script to drive a tachometer on Raspberry Pi GPIO using PWM

![Screenshot](/tacho-network.jpg?raw=true "Network traffic MB/s")

## Required hardware and schematics

 The components needed to drive a standard automotive RPM gauge are

 pretty simple. You need:

   - 12V power source (or battery) for the gauge

   - Optocoupler 4N25 to separate the gauge signal and Raspberry Pi GPIO.

   - 75 (or so) Ohm resistor for optocoupler input

   - 20kOhm resistor for pull-down for gauge signal line (might depend on gauge)

The script assumes BCM GPIO 4 (Pin 7 in Rasperry Pi) to be used for

driving the gauge. Pin 9 is used for the ground. Opto-isolator acts like

normal led, so putting a small ~75 Ohm resistor makes it ok with 3.3V.

The Hz is calibrated to [specific hardware](http://biltema.se/sv/Bil---MC/Bil-tillbehor/Bil-el/Instrument/Varvraknare-32251/) using the calibration array in the beginning of the script. You probably need to adjust the numbers 

here to make it match your hardware. Mine had huge variations especially between 4 to 6.

## Operating modes

Run the script by giving the operating more as the first parameter:

- test - Goes trhough test cycle setting values from 1 to 8

- [value] - displays the given float value between 1-8

- cpu - displays CPU load percentage from 0 up to 80%

- network - displays network inbound traffic in MB/s.

- mqtt [server] [topic] - subscribes to MQTT broker / topic for values.

Optional 'quiet' parameter disables the console output.

For example the following puts the script to refresh CPU on the background

    sudo ./tacho.py cpu quiet &

Note, that because GPIO on RPi needs root access 'sudo' must be used.