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Revision as of 13:49, 19 March 2012 by Tom (talk | contribs) (Pinout)

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This is the documentation page for the SPI_3FETs board.


The board has 3 fets that allow you to pull a pin of a load low. You would normally tie the other end of your load directly to the powersupply.

About 5A per output should be possible. Maximum voltage is 30V.

You will have to provide your own protection circuits if you are going to drive inductive loads (like a motor).

Assembly instructions

None: the board comes fully assembled.


The 3fets board is capable of sinking about 5A per output. We have tested A and the FET became slightly warm, as predicted by theory.

Although the specifications for the FETs allow a larger current, it is not recommended to exceed the 5A

Possible Configurations

External resources


The FETs

Additional software

Related projects


For the SPI connector see: SPI_connector_pinout.

The output connector is connected as follows:

pin function
1 OUT0
2 OUT1
3 OUT2
4 V+
5 V+
6 V+


The only LED is a power-LED.

Power connector

jumper settings

See solder jumpers on how to change the solder jumper.

By changing the solder jumper SJ1, you can make the connector nearest the board edge into the ICSP programming connector for the attiny44 on the board.


To make the 3fets PCB do things, you need to send things over the SPI bus to the PCB.

The general overview of the protocol is here.

The specific commands for the 3fets PCB are explained on the page about the spi_dio board, as the two boards share the same protocol: spi_dio_protocol . Where the SPI_DIO drives an output high, the 3fets board will drive the output pin LOW when the pin is driven active.

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 the dio and 3fets boards as well.

The software

Default operation

Future hardware enhancements

Future software enhancements

TODO: write a library to make handling this board easy.



  • Initial public release