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Revision as of 16:23, 11 May 2012 by Rew (talk | contribs) (Protocol)

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The SPI_Servo PCB
The Servo PCB (SPI version photographed)

This is the documentation page for the SPI_servo and I2C_SERVO boards.


This module enables you to easily control upto 7 servomotors over an SPI or I2C interface, while needing minimal resources from your CPU. The PCB is equipped with two SPI or I2C connectors, so daisychaining multiple SPI or I2C modules is possible.
This allows you to control a chain of boards with only 4 data lines (MOSI, MISO, SS and SCK) for SPI or two lines (SDA, SCL) for I2C. This is not only pin-saving, but is is also possible do daisy-chain multiple modules (we will be releasing even more boards with other functions in the very near future)!
The board can be used with all microcontrollers, such as the Atmel AVR, Arduino/Freeduino boards, Microchip PIC, Raspbery PI etcetera.

For small servos, the power supplied by the SPI or I2C connector is enough. However current surges of up to a whole ampere are easily achieved even when two or three smaller servos need to move simultaneously. For larger servos however, the voltage drop may be to high. We suggest conneting an auxillary 5V power source to the PCB, and move the jumper.

External resources


The CPU:

Additional software

Related projects


The pinout is standard for servo-motors; Pin 1 is GND (near the edge of the board) Pin 2 is VCC (5V) Pin 3 is data


The only LED is a power-LED.

Jumper settings

Solder jumper (on bottom layer): ICSP-Enable. CAUTION! Pin 1 and 2 are connected by a narrow PCB track. Cut this if you want to change this jumper setting.
1-2: Default: Both SPI connectors connected in parallel.
2-3: ICSP enabled; programming the MCU over the 6-pin connector. This connector may be marked SPI1 or SPI3 (near the edge of the board, furthest from the CPU.)


For the intro to the SPI and I2C protocols read: SPI versus I2C protocols

The board specific protocol can be found here: Servo_1.0_protocol

You should also read the General_SPI_protocol notes.

For arduino, a sample PDE is available, called ardemo_lcd.pde, also at BitWizard software download directory .

This is a demo to send things using SPI to the lcd board. The SPI routines there are applicable for SERVO boards as well.

The software

Default operation

Future hardware enhancements

Future software enhancements



  • Added jumper/power connector for (external) servo power.


  • Initial public release