My 2008 Mazdaspeed3 has a small portion of the LCD dashboard display that shows either a clock or a trip computer function (current fuel economy, miles to go, etc), but only one of these at a time. I prefer to keep the “miles to go” function displayed, so the car needed a proper dedicated clock. Here’s a picture of the finished clock installed in the dash. The three buttons below the clock are for setting the time and for changing to a stopwatch/elapsed time mode.
The circuit board is built on a piece of perfboard. There are actually very few components – the main parts are a PIC16F876, a handful of transistors, and a voltage regulator. The ribbon cable connects to the display board, and the small cable harness connects to a tap on the radio’s power supply leads. The display is a 4 digit blue common anode LED module from Sparkfun Electronics
. It is also mounted on a piece of perfboard with a header connector on the back for connection to the ribbon cable coming from the circuit board.
Here’s the schematic for the clock. The PIC is programmed in assembly language to drive the clock functions. The common anodes driving the digits are powered from the transistors. The individual segments are powered directly from the PIC. The voltage regulator delivers a stable 5V to the PIC. When the car headlights are turned on, the DIM input sees 12 volts, which causes the PIC to dim the clock display for nighttime viewing.
The lower dash module removes easily from the Speed3 by removing two screws and then pulling forward. Once the wire harnesses for the lighter and illumination bulbs are disconnected, the unit can be removed from the car. I cut a hole to fit the LED display module and used a piece of smoked plastic from an old alarm clock to make a bezel to dress it up. 4 small screws with their heads filed flat hold everything together. The three pushbuttons for the clock and one for the CAN Bus Monitor are carefully drilled in the dash unit as well.
The circuit board is mounted in a plastic project box, which connects to the modified dash unit. Also shown in the photos is my CAN Bus Monitor box. The clock control box is attached using some self-adhesive velcro strips behind the dash. There’s actually quite a bit of room back there for this to mount.