RPi SPI wheezy
In this guide, I will show you how to get SPI up and running on a Raspberry Pi, and how to control a SPI_LCD module. We will start from scratch, with a blank SD card.
Things we will be using
- Raspberry Pi
- 2GB (or larger) SD card
- Power supply for your Raspberry Pi
- Ethernet cable
- SD-card reader
- RPi Serial Breakout board
- SPI cable
- SPI LCD
Not necessary, but useful:
- Monitor with HDMI (or DVI and a HDMI-DVI adapter)
- HDMI cable
Software we will be using
- Raspbian "wheezy" image for Raspberry Pi, with hardware floating point support
- Script to enable SPI and I2C, and to update your Pi's software
Unpack the Raspbian image, and download the script. I advise on making a seperate directory for this project, and put all the files there.
Preparing the SD card
First, we will flash the SD card with the Debian image. Plug your SD card in your favourite reader, and into your PC. My SD card became /dev/sdc on my laptop, your mileage may vary.
Copy the image to your SD-card:
sudo dd if=debian6-19-04-2012.img of=/dev/sdc
This may take some time, depending on the speed of your SD card, and card reader.
Next, we need to move the modified kernel image and modules to the freshly flashed SD card. For this, you need to mount the partitions on your SD card. Im lazy, and just unplug my card reader, and plug it back in. Ubuntu then automagically mounts the two relevant partitions.
You will see a small (56MB) partition (mounted as /media/1AF7-904A on my system), which is the /boot partition/directory. You will also see a larger (approx 1.7GB) partition, containing all other data (mounted as /media/8fe3c9ad-c8f5-4b39-aec2-f6e8dba743e0 on my system). You may need to change the target directory in the following commands.
Copy the relevant script:
cp bw_upgrade /media/8fe3c9ad-c8f5-4b39-aec2-f6e8dba743e0/home/pi/
Make sure the script is executable:
chmod 755 /media/8fe3c9ad-c8f5-4b39-aec2-f6e8dba743e0/home/pi/bw_upgrade
And your SD card is ready!
Unmount your CD card
sudo umount /media/8fe3c9ad-c8f5-4b39-aec2-f6e8dba743e0 sudo umount /media/1AF7-904A
And remove the SD card from your reader.
Will be written ASAP.
connecting the hardware
We recommend you have/buy the rpi_serial board. It breaks out the SPI and I2C busses of the raspberry pi. This allows you to use a simple straight through 4- (I2C) or 6-pin (SPI) cable to connect the raspberry pi to the LCD board. The cables are available from our shop as well.
Connecting the SPI version of the board to raspberry pi without any interface logic is not recommended: The LCD board needs to run at 5V because the HD44780 only works at 5V. The MISO line is then driven by the board at 5V level, which is said to shorten the life of the BCM2735 significantly.
The I2C version of the board can be wired directly to the rpi with four wires.
If you're using SPI, please use the spi0 port for now for the purpose of this tutorial.
You might want to hook up your pi to a monitor, but I usually find that to much of a hassle. Hooking up your Pi to your network, however, is necessary.
Mount the RPi-serial board on your Pi, connect the SPI cable to the SPI0 port (mind the polarity!), and connect the other end of the SPI cable to your SPI_LCD module.
Plug your freshly flashed SD card in your Pi, hook up power, and your Pi will boot.
SSH into your Pi. If you have a monitor attached, your Pi will tell you it's IP address: "My network IP address is 192.168.1.116" (or an other IP of course). If you don't have a monitor attached, you need to check your routers logs to find out which IP your Pi has.
SSH into your pi:
ssh 192.168.1.116 -l pi
The default password is "raspberry"
Run the script (this may/will take some time):
And now, it's time to play! Let's try to display our first text:
sudo ./bw_rpi_tools/bw_spi/bw_lcd -T 0,0 'Hello World!'
If you did everything right, you now have "Hello world!" displayed on your LCD. Have a look at the source of bw_lcd, or its Raspberry_Pi_LCD_program manual for other options.
The bw_lcd program can also be used to control all of our other SPI boards, using the -a, -r, and -v switches.
sudo bw_lcd -a <address of the board> -r <register> -v <value>
Let's try this with a SPI_LCD, by clearing the screen. The display is at address 82, the register is 0x10, and the value doesn't matter. Caveat: The address should be given in hex, but the register and value in decimal.
sudo bw_lcd -a 82 -r 16 -v 0
Now your display should be cleared.
Note: We have written a new program, bw_tool, which is also capable of controlling our SPI boards. However, we still need to write the documentation for it. The program and sources are located in ~/bw_rpi_tools/bw_tool .
If you managed to get everything in this howto working, you should be able to control the entire range of BitWizard SPI boards. Good luck, and please show us your projects!
If you have any problems, please let us know, and we will do our best to help you resolve them. You can email us, or post your problem in our forum. We will respond as soon as we can.