TMF1901
Posts: 1
Joined: Wed Apr 10, 2019 10:43 am

Car Digital Dashboard

Wed Apr 10, 2019 10:55 am

Hi,
I am rebuilding an old landrover defender 90 it has no onboard computers or digital sensors. I am planning to use my raspberry pi as a dashboard but I didn't really know how to go about making one or what software/ hardware I would need. I am hoping someone would be able to give me some pointers on how I could make a digital dash. It would need to display rev fuel level and speed.
Thank you

Idahowalker
Posts: 445
Joined: Wed Jan 03, 2018 5:43 pm

Re: Car Digital Dashboard

Wed Apr 10, 2019 11:36 am

TMF1901 wrote:
Wed Apr 10, 2019 10:55 am
Hi,
I am rebuilding an old landrover defender 90 it has no onboard computers or digital sensors. I am planning to use my raspberry pi as a dashboard but I didn't really know how to go about making one or what software/ hardware I would need. I am hoping someone would be able to give me some pointers on how I could make a digital dash. It would need to display rev fuel level and speed.
Thank you
Well, you'd need to tap into the spark distribution line, a transformer type of tap would work, count the pulses, and divide by the number of cylinders to get the RPM's. For the fuel gage, I'd buy a replacement fuel gage, for bench work, and learn how to read the resistance at its various positions, converting those resistance values into a digital format, for the speed, I'd get a GPS module, which now gives you more options of data info and use the GPS device for speed over ground. I'd take the devices to be used and figure out which display device I want to use.

For the GPS, I'd leave it on all the time, even when the rest of the unit is powered off. I use an Adafruit Ultimate GPS, which uses in the uAmp range to keep up with tracking.

You may find that you want to put the individual components in different location, which would require a buss for digital communications. I'd use the CAN buss.
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thagrol
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Re: Car Digital Dashboard

Wed Apr 10, 2019 3:06 pm

TMF1901 wrote:
Wed Apr 10, 2019 10:55 am
It would need to display rev fuel level and speed.
Thank you
Speed is the tricky one. If you're plannig to use the vehicle on public roads your speedometer will need to be accurate within any margin required by the law in your territory. Last time I checked in the UK that was within 10%. Your dashboard as a whole will likely have to comply with whatever additional regs apply for accuracy, number and type of instruments etc.

Old school speedos (i.e speedos from pre engine management system cars) took a mechinal feed from the gearbox's output shaft to turn a pointer against a spring in the speedo. Gearing in the mechanism was used to correct for the final drvie ration (i.e. further changes in rotation between the gearbox output and the wheels). You'd need to duplicate that.

To complicate things further, the ratio between output shaft revolutions and wheel revolutions (hence speed) is affected by wheel and tyre size as well as gearing in the differential(s).

If you know all the ratios, the gear the car is currently in, and the engine RPM it should be possible to calculate speed from that. Calculating speed from GPS updates is also possible but won't work in arteas of poor/no signal so may not be legal as the vehicle's sole speedo.

Fuel tank level should be easy. I'd expect it to be just an analogue float sensor feeding the gauge. It'll just be a matter of scaling it's ouput to a suitable range and feeding it to an ADC.

As for engine RPM, if the vehicle had a rev counter it will likely have been driven in a similar manner to the speedo: a mechanicle cable from the engine's output stage to the gauge. If it didn't you're into counting spark pulses (which are very high voltage) or rigging up some sort of sensor on the flywheel.

Lastly, don't forget that any car is a hostile environment for electornics and you'l need to find some method of performing a safe shutdown and fast restart for the Pi. It's probably not a good idea to have to wait two minutes after you start the car before your dashboard comes online, or if your dashboard goes down while driving.

If the above sounds negative, that's because it is. You're talking about systems that are critical to the safety of the driver, passengers, and other road users. As such this shouldn't be undertaken lightly.
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