Speedometer Corrector #1
A couple of years ago, when I was getting ready for bigger tires and a gear change, I built a digital speedometer corrector. It's designed around an Arduino Pro Mini (a standard Arduino, same AVR processor as the Uno, but tiny and without the USB interface).
It's based on a design by Tom M'Guinness for his 1986 Porsche 944 Turbo.
I modified his hardware a little to work with the TJ. I tweaked his firmware just a tiny bit, but it's still 98% Tom's code. He used a pot to adjust the correction factor. That's really convenient, but I wanted exact repeatability and the ability to step to the next notch up or down, so I used an 8-bit DIP-switch instead. Less convenient, more exact. Frankly, I don't know which one I like better.
This was a first go at it, and I expected to have to alter it, so I did nothing to make it small. It's on a sea-of-holes breadboard in a 4.5" x 3.5" x 2" box. I wired the cable into a pair of OEM connecters and plugged it in between the vehicle wiring and the speed sensor. That makes it easy to remove, and no OEM wires were cut. I ran the cable through a hole in the tunnel under the console, to sit under the driver seat. I had planned to eventually shrink it, and move it under the dash or under the hood.
I installed it, calibrated it, and enjoyed it. I went from 31" to 33" tires, calibrated it again, and enjoyed it. Switched from 3.73 to 4.56 gears, calibrated again, and enjoyed it. It's very accurate, and has worked perfectly for over two years.
I eventually found that I didn't need a support chip, so I removed it and jumpered across pins in the socket. That's the only tweak I've done to it (and it's possible that some TJs would need that chip, it's a Schmitt Trigger to clean up the signal from the Vehicle Speed Sensor).
I recently placed the design on GitHub:
https://github.com/OldBuzz/Speedometer-Corrector-Arduino-based
I do not plan to develop this one any further, or shrink it.
But wait, there's more...
A couple of years ago, when I was getting ready for bigger tires and a gear change, I built a digital speedometer corrector. It's designed around an Arduino Pro Mini (a standard Arduino, same AVR processor as the Uno, but tiny and without the USB interface).
It's based on a design by Tom M'Guinness for his 1986 Porsche 944 Turbo.
I modified his hardware a little to work with the TJ. I tweaked his firmware just a tiny bit, but it's still 98% Tom's code. He used a pot to adjust the correction factor. That's really convenient, but I wanted exact repeatability and the ability to step to the next notch up or down, so I used an 8-bit DIP-switch instead. Less convenient, more exact. Frankly, I don't know which one I like better.
This was a first go at it, and I expected to have to alter it, so I did nothing to make it small. It's on a sea-of-holes breadboard in a 4.5" x 3.5" x 2" box. I wired the cable into a pair of OEM connecters and plugged it in between the vehicle wiring and the speed sensor. That makes it easy to remove, and no OEM wires were cut. I ran the cable through a hole in the tunnel under the console, to sit under the driver seat. I had planned to eventually shrink it, and move it under the dash or under the hood.
I installed it, calibrated it, and enjoyed it. I went from 31" to 33" tires, calibrated it again, and enjoyed it. Switched from 3.73 to 4.56 gears, calibrated again, and enjoyed it. It's very accurate, and has worked perfectly for over two years.
I eventually found that I didn't need a support chip, so I removed it and jumpered across pins in the socket. That's the only tweak I've done to it (and it's possible that some TJs would need that chip, it's a Schmitt Trigger to clean up the signal from the Vehicle Speed Sensor).
I recently placed the design on GitHub:
https://github.com/OldBuzz/Speedometer-Corrector-Arduino-based
I do not plan to develop this one any further, or shrink it.
But wait, there's more...
