Files from my forays into programming for the Raspberry Pi.

Includes programs written in C, Python, Javascript, and a little Scratch.

Libraries used: RPi.GPIO, gpiozero, wiringPi, pygame, python-cwiid, and soon Pygame Zero.

If anyone is interested enough in any of the below programs to read an expanded blog article with diagrams and more code explanation, please contact me and I will write one.

Use make to build the programs in here.

Uses the PWM pin, physical pin 12 (GPIO18). The clock divisor, range, and duty cycle value can all be set from a menu. It has been tried with an LED, a speaker, and a 6V motor connected to the collector side of a PN2222 transistor.

I have also tried it with a servo, setting it up for 50Hz (20ms cycle time). The duty cycle need s to be kept very low.

The frequencies quoted in the program have now been checked with a multimeter that has a frequency function.

General python programs.

Test the resolution of time.sleep().

It appears to be about 100us (microseconds), which is an order of magnitude (or more) better than I expected. time.sleep(n) ALWAYS sleeps for at least the time specified.

A few programs to flash LEDs etc.

Flashes an LED attached to Pin 12 (GPIO18).

Flashes two LEDs alternately, attached to pins 12 and 26 (GPIO18 & GPIO7).

Makes a 1kHz (ish) tone from a speaker attached to pin 12 (GPIO18).

A driver library for LCD displays attached to GPIO pins in a 4-bit configuration The connections have been updated and the pin numbers changed to use BCM numbering (see comments in the file for details).

When run directly, it starts by initializing the panel and writing 'SETUP'. Then it waits for the user to hit enter between each of the next phases: position the cursor to the beginning of the second line and write 'Second Line', then write 'End' at the end of the second line, after which the cursor is shown, hidden, and set blinking before finally waiting for the user to hit enter again and then disconnecting from GPIO.

An updated version of the drive_lcd program, specifically for a 20x4 display. There is more cursor addressing in this one to reflect the extra lines.

Drive a slightly strange 128x64 display. It seems that most either have an I2C or SPI interface, or 8 data bits and 2 chip selects. The one I bought is different, and has strange GDRAM addressing instead.

It turns out that mine would work on SPI too. it works perfectly connected to an Arduino using the U8glib library.

See python/st7920 below

Displays a clock on the first line of a connected LCD display using the drive_lcd library. See drive_lcd for the connection details. It ensures that it always releases the GPIO pins by having a try...except round the main loop to trap Ctrl-C.

Show the top line from the Delorean display, and the second line is the current time.

Drive a seven segment, common-anode, display. Connections can be seen inside the file. Currently set up for B+, assuming a 40-pin GPIO.

First, it shows 0-F with a delay between each. Then, it shows 6 arrows pointing forward and back, right and left. Finally, it shows each possible letter and waits for the user to press enter.

The simplest way to change to a common-cathode display would be to swap the names of segment_on() and segment_off().

Simulate a (British) set of traffic lights with a Red, Amber, and Green LED connected to pins 11, 13, and 15 respectively.

Turn a motor on and off connected to pin 12 via PN2222A transistor.

I wrote this so that I could turn the motor off quickly in case I'd made a bad choice of transistor or another schoolboy error. The motor is connected to the collector and powered by a wall-wart providing a range of voltages, I tried 6V and 9V, but I initially tried it with the 5V line (pin 2) on the Pi GPIO and that was fine too.

it turns out that my choice of transistor was OK. With pin 12 connected via a 4K Ohm resistor to the Base of the transistor, I'm drawing less than 1mA from the Pi. The motor is drawing around 180mA when running freely. I'm going to try stalling the motor a little to test its maximum draw once I have some crocodile clips.

Read a Light Dependent Resistor using the RC charge time of a capacitor. See comments inside for details.

The circuit I used is a little different from the one suggested in the GPIO Zero documents for Light Sensor

Drive a servo connected to pin 25 using software PWM. I don't think it's very practical, but that may be more to do with the low quality servo I'm using. The software PCM is wavering between about 47Hz and 51Hz whereas the servo really wants a steady 50Hz.

To drive a servo accurately needs the hardware PCM on GPIO18, I believe.

Drive a quad 7 segment display as a clock. clock drives a common-cathode display and clock-ca drives a common-anode display. See this Raspi.TV page for wiring details.

Examples using the GPIO Zero library.

Using gpiozero library, switch a LED connected to GPIO17 on and off with a button connected to GPIO21 and a GND.

Emulate a complete British Puffin crossing. It has Red, Amber, and Green LEDs for the cars, obviously. It uses a Red and Green LED for walk / don't walk for pedestrians. It also uses another Red LED to indicate that the crossing request button has been acknowledged.

Drive a common-cathode RGB LED.

Run a CamJam Edukit 3 Robot. Takes input from the user:

f   <n>     Forward for n steps
f   d       Forward until less than 10cm from obstacle
b   <n>     Backward for n steps
l   <n>     Left for n steps
r   <n>     Right for n steps
q           Quit

Control the battery-powered Christmas fairy lights that I bought this year. It randomly fades in and out and flashes at a couple of different speeds.

Adventures in game / UI programming.

Bounce a (square!) ball around in a window.

Bounce a ball around in a box with a bouncy sound on each bounce. Use the cursor keys to expand and contract the square that the ball is bouncing in.

Display buttons that turn LEDs on and off. Five buttons turn directly connected LEDs on and off. Another seven buttons turn the segments of a display on and off. Ten more buttons display the digits 0-9 on the 7-segment display and a final 25 buttons allow for most of the alphabet in upper or lower case.

See main.py and .../gpio/drive_7_segment.py for full connection details.

Examples using the python-cwiid library. The main CWiiD library information.

An example of using a Wiimote on a Pi, displays the state of the buttons and the accelerometer data. It's a bit flaky with the £3.99 Wiimote clone that I bought from eBay, It's a lot more stable with a genuine Nintendo one, the rather noisy library can be squelched by using

    wiimote.py 2>/dev/null

if necessary.

The beginning of a program to show the values returned from the accelerometers with the Wiimote in different orientations. I have abandoned it for now because my Wiimote clone is so flaky that there's no point continuing.

Library for a 128x64 ST7920 panel connected via SPI based on Jamie Wood's ST7920 library.

Test the library by plotting a single pixel, drawing a rectangle, filled rectangle, and reverse filled rectangle, and outputting text which shows how long each redraw takes (~114-118ms on my RPi2).

Show the IP address on the display. This could be used on a headless Pi to show its address to allow logging in via SSH.

These are programs to drive a robot based on the CamJam Edukit 3.

Turn on both motors in one direction for 2 seconds.

Move forward for a second, right for a second, and then left for a second.

Read the line-following sensor. Returns low (0V) for Black, and high (3.3V) for white. It works at a distance of ~2.5cm (~1").

Read the ultrasonic distance sensor. This returns high for the echo flight time. This is then turned into a distance in cm.

A voltage divider is necessary to connect this to a Raspberry Pi because it is a 5V peripheral. A 470R and a 330R resistor (provided in the EduKit 3) gives about 3V.

Use the software PWM in the Rpi.GPIO library to drive forward, right, and left at about 30% power.

Turn on all 4 lines. I was having trouble with the supplied H-bridge driver board, so I needed to turn on all 4 lines that the board uses so that I could connect my multimeter and see if there was voltage, which there wasn't with even one motor connected.

NB: This should not be run with motors connected.

Read a MCP3202 12-bit A/D over SPI.

Use the Adafruit I2C library to drive a normal LED connected to the first pin, an RGB LED connected to the second, third, and fourth pins on a MCP23017 chip, changing its colour every time a button connected to the fifth I/O pin is pressed.

A Blynk library client program that updates Virtual Pin 9 with the seconds from the current time, responds to a slider on V1, updating a graph attached to V4, and has a terminal on V3 which feeds back and sends notifications.

The beginnings of an alien game. N.B. I can't draw :-)