ATMEL 8535 Microcontroller software for ignition timing


As part of my ongoing effort to avoid buying a new car I wondered if I could improve the performance and economy of my car ('76 Golf) by varying the ignition timing. I wanted a control on the dash so I could make adjustments while driving and see the effects.

I built a box that fits in the radio slot in the dash and has a display and adjustment dial on the faceplate. The ignition timing is controlled by an ATMEL 8535 microcontroller which monitors the pulses from the distributor and produces pulses to drive the ignition coil. The software contains a table of timing offsets and the relevant entry is determined by the RPM and vacuum setting. Adjusting the dial on the box will change the relevant entry when update mode is enabled. The offsets table can be saved to EEPROM.

Please note that there is no ready-made hardware for this project. Testing using the prototype didn't show any dramatic improvement and the market is severly limited as most cars now have an ECU and fuel injection. However, the hardware for this project is simple and I can supply details if requested. I made a plastic case to fit where my car radio isn't. The circuit board and processor are on the left and the plug on the right is the connection to the car electrical system.

front view   top view

The user interface is (left to right) :

When the mode switch is down (normal mode) the RPM and advance are displayed and the pot and buttons are ignored.

When the mode switch is centered (maint mode) or up (update mode) the display contains more info and the YES button can be pressed to access the menu functions.

When the mode switch is up (update mode) the position of the pot is loaded into the current timing offset entry (+/- 22 degrees max).

The keyboard menu contains functions which are selected by positioning the pot and pressing the YES button. Pressing the NO button will end the menu display.

Download ignition timing control software

Circuit board layout || Circuit schematic || Notes for schematic

Last Modified : 2007-03-04