Category Archives: Controls

ThumperFI – Single-Cylinder Motorcycle EFI Controller

What started as a summer project morphed in to today what I like to call ThumperFI – “thumper” from the characteristic sound associated with single-cylinder dirt bikes and “FI” for Fuel Injection. I started the project with the intention of fuel injecting a lawn mower as a sort of in-depth introduction to fuel injection before I started work in the Internal Combustion Engines lab at school. However, the project quickly increased in complexity as my goals became loftier (and I maxed out the inputs to the MyDAQ) until it became a full-fledged system for controlling any single-cylinder engine.

Assembled ThumperFI v1.0 board

Assembled ThumperFI v1.0 board

The system is based around the Atmel ATMega644 8-bit microprocessor. Among it’s many features:

  • On-board serial-to-USB converter (FT232RL)
  • Variable Reluctance CPS (MAX9924)
  • Flyback protected injector output

There are 6 analog inputs to the system, which uses speed-density to calculate airflow. The analog inputs are:

  • Manifold Absolute Pressure (MAP)
  • Intake Air Temperature (IAT)
  • Coolant Temperature (CLT)
  •  Throttle Position (TPS)
  •  Wideband O2 (UEGO)
  • Battery Voltage (BATT)

The firmware is written C and compiled by the AVR-GCC compiler in AVR Studio 6. User configuration and tables (warm-up table, MAP-RPM VE table, etc.) are stored on the external 16kB EEPROM.

The driving force behind this project has been my own desire to learn and grow in both my field of study (mechanical engineering) and other, related fields of study (computer, electrical engineering) as well as learn about engines and controlling them. Since starting this project I have attained experience in:

  • Use of oscilloscope for general measurement and circuit debugging (TDS 320)
  • Use of digital logic analyzer (USBee ZX)
  • Familiarity with engine control sensor use and operation
  • Circuit construction, design and debugging
  • Component selection and sizing
  • Basic engine fuel control algorithms and theory
  • Reading data sheets
  • Microcontrollers and embedded programming
  • Project management and documentation
  • Soldering, both through-hole and SMD (with Weller WES51)
  • PCB layout and assembly

Needless to say, I’ve learned quite a lot – and I’m always learning more each day. Two weeks ago I put the finishing touches on my communication scheme and implementation. Over winter break (2013) I received my PCB from the fab, spent 10 hours soldering it, tested it and only had to make two slight modifications.