This is the speedometer replacement I made for my trusty old VW Beetle (1973). The main processor (another DS5000), display and indicators are inside the original speedometer housing. The analog to digital converter is in a separate aluminium box under the hood.
The speed sensor is made of a sensorwheel from a PC mouse and is driven by the original speedometer cable in a 1:1 ratio to the front wheel revolutions. Each revolution results in 45 ‘ticks’ on the timer input.
By calculating the circumference of the wheel the speed and distance calculations could be determined. With the current wheel size every 100 meters there are 2222 ticks on the timer. The display updates ones every second so the speed indicator is nice and steady during driving.
I also had the opportunity to add a ‘daytrip’ counter along with the total amount of kilometers driven, a clock, voltage indicator and of course the fuel indicator.
Since the DS5000 has battery backed SRAM as its main storage the clock, distance and daytrip values are not lost when the system is switched off.
The fuel indicator in the original speedometer is attached to a fuelsender which ‘ burned out’ several times in my VW due to the old stabilizers intermittent failure.A common problem with the Beetle
In the new setup the current through the sender is kept at a constant value and the amount of fuel is determined by reading the voltage across the sender so hopefully the sender will last a lot longer now.
Programming and ‘dry run’ on the bench:
Inside the car
The ‘Bootsplash’ I added which is shown briefly during ‘ignition on’ (camera was a tad bit slow)
The display is a 120×64 backlit LCD
The external (I2C driven) A/D converter box (note: the TEMP and RPM inputs are not yet used)
Here is a link to the C source of the system:
Future plans include a color LCD, a ‘rev counter’ and maybe some more indicators for other functions.