3FETs
This is the documentation page for the SPI_3FETs and I2C_3FETs boards.
Overview
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 power supply.
About 5A per output is possible. Maximum voltage is 24V.
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.
Specifications
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
Datasheets
Additional software
Related projects
Pinout
For the SPI connector see: SPI_connector_pinout.
For the I2C connector see: I2C_connector_pinout.
The output connector is connected as follows:
| pin | function | |
|---|---|---|
| 1 | OUT0 | |
| 2 | OUT1 | |
| 3 | OUT2 | |
| 4 | V+ | |
| 5 | V+ | |
| 6 | V+ | |
| 7 | GND | |
| 8 | GND |
LEDs
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.
Protocol
To make the 3fets PCB do things, you need to send things over the SPI or I2C bus to the PCB.
For the intro to the SPI and I2C protocols read: SPI versus I2C protocols.
In case of SPI, please read the General_SPI_protocol notes.
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: 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.
Some 3fets boards were shipped with software that would default the outputs to inputs. On those you need to set all pins to outputs by sending 0xff to register 0x30.
For arduino, a sample PDE is available, called ardemo_lcd.pde, also at the 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.
Changelog
1.0
- Initial public release