Brian Benchoff Upgrades 1980s Electric Car with CAN-Enabled Digital Gauge Cluster
This Comuta-Car's new dashboard looks retro but uses modern tech.
Sometimes, the easiest way to upgrade a device is by replacing everything! This principle was applied when Brian Benchoff gave a digital upgrade to a 1980s Comuta-Car's gauge cluster.
"How I used Two Million transistors to replace four relays."
Benchoff's long-term project is modernizing a Comuta-Car while keeping the 1980s nerd aesthetic. These electric automobiles featured lead-acid batteries powering a (up to) six-horsepower DC motor. You might also recognize these cars as their predecessor, the Citicar.
An early upgrade Benchoff made was replacing the electric drive with an AC induction motor and a modern speed controller. Unfortunately, this change meant the stock speedometer was no longer usable since it uses a cable connected to the original motor shaft. Benchoff needed another solution for this critical meter to keep the upgraded car street-legal.
Fortunately, the modern motor controller provides speed information via the CAN bus. Almost all modern automobiles communicate with devices via the CAN bus. So, with a handful of microcontrollers and CAN PHYs, this Comuta-Car got a significant digital upgrade inside and out.
A 1/8-inch thick aluminum plate held the original gauge cluster components. The new metal plate is twice as thick as the original and contains a dense LED matrix, a key switch (ignition), a custom-made rotary knob for selecting the gear, and four accessory switches.
The centerpiece display contains 702 LEDs configured in an 18 x 39 matrix driven by an IS31FL3741 IC. An Adafruit Feather M4 CAN Express interfaces with the CAN bus to receive information about the vehicle's speed, turning the display into a speedometer and odometer. Since the battery management system is on the CAN bus, this display can also provide the Lithium battery's state-of-charge and estimate the vehicle's range.
Drive, Neutral, and Reverse make up the gear selections. A custom-made rotary knob with a 16-segment LED indicator at its center provides this interface. Benchoff says the satisfying aspect of this arrangement is that the segmented LED stays put while the knob's outside ring moves.
Four switches on the other side enable the lights, windscreen wiper, defroster, and hazard flasher. In the original electrical system, the switches enabled a relay. The upgraded design features a MOSFET with a shield-like secondary card that attaches each device with screw terminals. An ATmega328P, the same processor found in the Arduino Nano, controls the MOSFETs and communicates with the CAN bus via a Microchip MCP2515 CAN controller and MCP2551 CAN transceiver.
Below those switches is a replacement panel for the former climate controls. The upgrade only features a 150-watt portable 12-volt heater for defrosting the windows. This accessory only needs a single switch. So, the replacement for the climate panel is mostly empty. This aesthetic reminds us of similar "blanks" found in production automobiles where optional features are missing. (Although none of those cars have a Party option, like this one!)
A maple burl veneer covers the entire digital gauge cluster and completes the look. You can learn more about Benchoff's Comuta-Car restoration project on this page. All design files are available here if you want to replicate this one-of-a-kind dashboard, including Party switch.