GPIO LEARNING BOARD
This is a simple board which connects to a Raspberry Pi (or compatible) computer's GPIO connector and provides some simple functions for experimenting with GPIO programming. The functions provided are:
- Red, Green, and Yellow LEDs which can be individually turned on or off.
- A pushbutton whose status can be read.
- A DHT11 or DHT22 temperature/humidity sensor
- A connector for an FTDI USB to serial adaptor which provides access to the serial port/console.
It is compatible with the Raspberry Pi 2, 3 or 4. It is not compatible with the Raspberry Pi version 1 which had a smaller GPIO connector. It will work with the Raspberry Pi Zero if it has a GPIO header installed.
The board is compatible with the GPIO connector on a Toradex Colibri i.MX6 series mounted on an Aster carrier board. Programming is slightly different from a Raspberry Pi as the GPIO devices names are numbered differently (see below).
If you use the official Raspberry Pi touchscreen, it uses two pins on the GPIO connector for power. This will conflict with being able to install the GPIO Learning Board on the connector. A couple of workarounds for this are:
- Connect the touchscreen using wirewrap or soldered wires to leave the GPIO pins free.
- On the GPIO Learning Board, use a GPIO header with long pins that extend from the top of the board and can be used to attach the touchscreen wires. See, for example https://www.buyapi.ca/product/gpio-stacking-header-for-pi-abpi-2-extra-long-2x20-pins/
See the file bom.csv.
Make sure the tactile switch has the correct footprint for the PCB.
Either a DHT11 or DHT22 temperature/humidity sensor can be used (they differ in price and accuracy). This can be omitted if desired. You can solder a header if you don't want to permanently solder in the sensor.
Any suitable LEDs can be used provided they have 0.1" pin spacing. You may want to adjust the values of R3, R4, and R5 slightly to make all LEDs similar brightness, depending on the LEDs used.
The GPIO connector needs to be a suitable "female" connector to connect to the Raspberry Pi. See the parts list.
The optional FTDI connector will work with most FTDI breakout boards such as the AdaFruit FTDI Friend or DFRobot Basic Breakout. The power pin is not used so it doesn't matter if it is set for 3.3V or 5V.
If you want to extend the board away from the Raspberry Pi or Toradex board, you could connect it via a 26-pin GPIO extension cable, which is available from a number of vendors.
Refer to the pictures of an assembled board to aid in construction. All parts are through hole, making them easy to assemble. Note that the GPIO connector mounts on the bottom (non silk-screened) side of the board.
The suggested order of installing and soldering is:
- 4 pin SIP for DHT11/DHT22 sensor (if used)
- 6 pin SIP connector
- GPIO connector
- DHT11/DHT22 sensor (if not mounted on a SIP)
The LEDs must be oriented correctly. Many LEDs have a flat side on the cathode pin which should be lined up to match the symbol on the silkscreen, hoever this convention is not consistent across all LEDs. A better indicator is the longer lead indicating the anode which should be on the left when looking at the top of the component side of the board with the GPIO connector at the top. A trick which often works to check the polarity and color of an LED it to connect it to a digital multimeter with the ohms function on the diode test range -- this usually supplies enough voltage to dimly light the LED.
Make sure the DHT sensor is oriented correctly. The silkscreen indicates how it should be installed.
Make sure all component leads are cut flush to the bottom of the board after soldering so they don't short anything when the board is installed on a Raspberry Pi.
When inserting the GPIO board into the Raspberry Pi or Toradex, be sure to orient it correctly as the connectors are not keyed and can be installed backwards.
The GPIO pins and device names are assigned as follows.
Raspberry Pi 0/2/3/4:
|Function||P1 Pin||GPIO Name|
Toradex i.MX6 series Colibri SOM with Aster carrier board:
|Function||P1 Pin||GPIO Name|
Sample programs for the Raspberry Pi (shell script and Python) are provided here. The DHT example requires downloading an AdaFruit DHT Python module.
To use the serial port, on the Raspberry Pi you can run raspi-config to enable a serial console and you should then be able to log in on the serial port using settings of 115200 bps 8N1. The device file for the serial port is /dev/ttyS0. On the Toradex Colibri with Aster carrier board, the serial port shows up as UART B with device file /dev/ttymxc1. By default there is no login process connected to it. You need to be root to read or write the serial port. See reference  below for more details.
This is Open Source Hardware, licensed under the The TAPR Open Hardware License. You are welcome to build the circuit and use my PCB layout.
Assembled and tested boards are available from me for a nominal cost. Check eBay for "Raspberry Pi GPIO Learning Board" from seller Sordnax. Contact me directly about purchasing larger volumes of boards at a discount.