CPU meter from an old Desynn avionics instrument

Show the min and max utilisation of CPU cores in your laptop. Connect via USB!

Original indicator use in for example Hawker Hunter

Several variants with different labels

https://en.wikipedia.org/wiki/Hawker_Hunter

External view https://www.jetphotos.com/photo/10868031

Cockpit photo https://www.jetphotos.com/photo/9365230

Circuit design

Six voltages 0-24 V

DAC for analog outputs variant?

Amplifier 0-2 V to 0-24 V variant?

Power amplifiers (voltage followers) transistors ?

Timer circuit monostable 74LS123

USB-to-SPI

FT232H https://ftdichip.com/products/ft232hq/

Adafruit Breakout board https://www.adafruit.com/product/2264

Here is the resulting schematics:

PCB design

Kicad https://www.kicad.org/

Software

Written in Python

Autostart with udev and systemd

Installation

Install the Python dependencies so they are available for the root user.

sudo mkdir /opt/cpumeter
sudo cp src/cpumeter.sh /usr/local/bin/cpumeter
sudo cp src/cpumeter_daemon.py /opt/cpumeter/
sudo cp src/95-cpumeter.rules /etc/udev/rules.d/
sudo cp src/cpumeter.service /etc/systemd/system/

udev

sudo udevadm control --reload
udevadm trigger
udevadm monitor
udevadm monitor --property
udevadm monitor --env

Start or stop the daemon

sudo systemctl daemon-reload
sudo systemctl restart cpumeter.service
sudo systemctl stop cpumeter.service

Show log file

sudo systemctl status cpumeter.service
journalctl -u cpumeter.service
journalctl -u cpumeter.service -f

Indicator working principle

Smiths desynn

See http://avionicengineer.blogspot.com/2011/03/synchronous-data-transmission.html

Discussion on https://www.youtube.com/watch?v=2iqJ6352u74