Main Atmega8 I2C Scoreboard Interface

This project provides a simple i2c interface for controlling two connected seven segment numbers. It optionally provides RGB PWM for two independent output ports and understands simple ASCII letters, numbers to be displayed on both digits and individual control of segments.

The software is intended for the board layout provided in the hardware repository.

Requirements:

• Atmega88p(a) (other microcontrollers may be suitable if the code is adjusted accordingly (ports, clock, etc.),
• A suitable flashing device,
• A suitable i2c controller, such as the raspberry pi with i2c-tools installed or similar.
• Fuses of the Atmega88pa should be set to -U lfuse:w:0xe2:m -U hfuse:w:0xdd:m -U efuse:w:0xf9:m (Brown out detection, 8 MHz internal oscillator) Efuse can potentially be read as 01 instead.

Example Schematics:

See the hardware repository.

Build:

Navigate to the debug or release folders and run make.

Usage:

The default i2c address of the atmega88p is 0x10. The device takes either no parameters with the command, 8 bits of data or 16 bits of data. The software can control two digits individually or use them combined to display numbers between 0 and 99.

Anything that cannot be interpreted as a command is interpreted as an ascii symbol to be output on the primary port. For example, sending 0x32 will print a 2 on digit 0. A non-printable symbol will be replaced by a dash (-).

• The virtual 16 bit registers 0x00 and 0x01 control the first PWM port. They take one 16 bit parameter. The upper byte of the parameter for 0x00 controls the pwm timing for the red component, the lower byte controls the blue component. 0x01 controls the green component. Values up to 0x01FF are acceptable, thus the green component has twice the pwm precision as the other two colors.
• The second PWM port is likewise controlled by 0x02 (rb) and 0x03 (g).
• Writing to the virtual register 0x04 disables PWM. The parameter given controls what colors on what port are enabled. Bit order is xxRrGgBb, where capital letters control the first, small letters control the second pwm port. Thus to enable port 0 with white light and disable port two completely, xx101010 could be used.
• Writing anything to the virtual register 0x05 reenables pwm.
• A byte written to the virtual register 0x06 is interpreted as a number and written to both digits.
• A byte written to the virtual register 0x07 is written as ascii to the first output (right).
• A byte written to the virtual register 0x08 is written as ascii to the second output (left).
• The registers 0x09 and 0x0B can be used to set individual bits on the first and second port respectively. Default bitorder for the parameter is GFEDCBA for both ports.
• The registers 0x0A and 0x0C can be used to clear individual bits on the first and second port, respectively. Default bitorder for the parameter is GFEDCBA.
• The Software supports a change of the i2c Address via i2c. Since this is dangerous to do in a live system, it requires a series of 2 commands for a temporary address change and a third command to write the new address to the eeprom. Please make sure that your address is valid (0x0F < address < 0xF0), otherwise your commands will be ignored.
  1. Write the new address two times simultaneously to 0x0D. For example, if the new address should be 0x12, write 0x1212 to 0x0D.
  2. Confirm the new address by writing it again two times to 0x0E. This will cause an immediate change of the i2c address. The device will now respond to the new address, but fall back to the old address if it is reset.
  3. Write the address to the eeprom by writing the old address and the new address to 0x0F. The old address must be the one currently stored in the eeprom. This defaults to 0x10 if no address was programmed before. For the example above, if the default address is still present, write 0x1012 to 0x0F.
• anything else written is interpreted as a symbol to be displayed.

Reading from the device with a generic read command will return the currently displayed digit.

License

See License.md.