Summary of Rally Gearshift Display
This device is a reliable gear indicator for rally cars, solving vibration-induced jitter and ambiguous 360-degree potentiometer readings between first and fifth gears. It features a dedicated calibration routine activated by a jumper, where the driver cycles through all gears to map unique values stored in EEPROM, ensuring accurate display on a large LED screen.
Parts used in the Rally Gearshift Display:
- Sequential gearshift mechanism
- Small potentiometer
- Main axis of the gearshift
- Large bright LED display
- Jumper for calibration mode
- Firmware with sorting logic
- EEPROM for storing values
This device was built at Recursive Software Development Labs in order to be mounted on a rally car competing in the Estonian National Rally championship.
The racing team needed help realizing a reliable measurement device which would output the currently inserted gear on a large, bright led display.
The biggest challenge to overcome was that the existing mechanical sequential gearshift would only allow enough room for a small potentiometer to be attached to its main axis, but the mounting mechanism is highly subject to vibrations, therefore after some time the readings would become unreliable or jittery.
Another problem was that when shifting from R until the 5th gear, the potentiometer would output identical readings both for R and 5 (as in, the axis would turn 360 degrees), making the first and the last gear undistinguishable.
This required to implement a dedicated calibration procedure, which is activated by switching oen jumper on the board.
Whenever the jumper is set, a calibration routine is started, which requires the driver to put all the gears, in no particular order, in sequence. The firmware takes care of sorting out the correspondences of the various readings with the inserted gear, and then stores the new values in the EEPROM.
For more detail: Rally Gearshift Display
- What was the main challenge with the existing gearshift?
Vibrations made small potentiometer readings unreliable or jittery over time. - How does the system distinguish between reverse and fifth gear?
A calibration procedure maps unique readings to each gear to resolve identical 360-degree outputs. - Can I calibrate the device while driving?
No, calibration requires setting a specific jumper on the board to activate the routine. - What order must the driver use during calibration?
The driver must put all gears in sequence in no particular order. - Where are the new gear values stored after calibration?
The firmware stores the sorted correspondences in the EEPROM. - Does the firmware sort the gear readings automatically?
Yes, the firmware handles sorting out the correspondences of various readings with the inserted gear. - What type of display does this project output to?
The device outputs the currently inserted gear to a large, bright LED display. - Why was a standard potentiometer insufficient without modification?
The axis turns 360 degrees, making the first and last gear undistinguishable without calibration.
