Raspberry Pi - HW/SW Application Development

Raspberry Pi HW/SW
Application Development
Make your own shield and control peripheral using RPi
Walter Dal Mut & Francesco Ficili

Intro to RPi
● Basically a Microcomputer on a ‘Credit Card sized’ board
● Based on a Broadcom SoC
● Many different interfaces: USB, Ethernet, HDMI, SD, TFT
Display...
Model B Model B+

...And a Mysterious Thing
● The RPi GPIO (General
Purpose IO) Connector
contains all low-level
interface of the board.
● Usually not known by high-level
software programmers.
● Well known by embedded
software developers.
● It’s the best choice to make
board functionalities
expansions.

Interface Options
● GPIO: the General Purpose Input Output is the most simple interface of the
board. It can writes or reads the status of a single pin.
● UART: the Universal Asyncronous Receiver Transmitter is one of the most
used serial standard in data communication. It’s the TTL level version of
the old PC RS232 interface (tty under Linux). It is a full-duplex point-to-point
standard.
● I2C: the Inter Integrated Circuit (aka I square C) is a communication
standard developed by Philips during ‘80. It’s a address oriented, half-duplex,
master-slave multidrop standard. It also support a multi-master
variant.
● SPI: the Serial Peripheral Interface is a communication standard
developed by Motorola. It is a master-slave multidrop full-duplex standard.

The ‘Shield’ Concept
● Shield Definition (from Arduino Website): “Shields are boards that can be
plugged on top of the Arduino PCB extending its capabilities”
● So a Shiled is, basically, an application-oriented expansion board that is
managed by the main board through one of its interfaces.
Example of RPi Shield
(GSM/GPRS Shield) Arduino ZigBee Shiled RPi to Arduino Shields
Adapter

Build a Custom Shield
● Many different type of shields available on the market.
● Sometimes the range of available shields could not fit a particular
application or you may have the idea of build your shield by your own.
● To build a custom shield you need:
○ An electronic CAD for design,
○ A PCB maker,
○ Shield components,
○ Assembly operations.
● Many PCB maker provide assembly
service.

KiCAD EDAS
● Many different type of EDAS (Electronic Design Automation Suite)
available nowadays: ORCAD, Mentor, Allegro, Altium Designer…
● Expensive Licensing, too complex for the task, too much tool inside the
suite… Not suitable for RPi shields development.
● Some free open source EDAS developed through years by electronic
entusiasts are now reaching a good maturity level.
● KiCAD is one of this tools!!!

Why KiCAD?
● Completely free and open source,
○ http://www.kicad-pcb.org/
● Cross-platform (Linux, MacOS and Win),
● Simple to use (getting started is only 27 pages long),
● Very large community of users that shares component libraries,
● Examples:
○ http://smisioto.no-ip.org/elettronica/kicad/kicad.htm (useful lid for
hobbysts)
○ http://kicad.rohrbacher.net/quicklib.php (component generator)
○ http://www.kicadlib.org/ (libraries collection)
○ … and many others

Suite Description
● It comprises a schematic
editor, layout editor, gerber
visualization tools and provide
a simple interface for output
files generation,
Kicad Project Manager

Layout Editor
Navigation Shield Layout

Examples
● Navigation Shield
○ GPS Unit (over UART link)
○ IMU Unit (over I2C link)
○ GP LEDs
○ Possible application: rovers or drone
navigation control
● Smart I/O Shield
○ 5 Analog Inputs,
○ 8 Digital I/O (2 PWM),
○ PIC18F2550 with I2C interface
○ Possible application: I/O expander for
RPI (acquisition, control…).

Build your prototype
● PCB (need gerber files):
○ Md srl: http://www.mdsrl.it/ (very professional service)
○ PCBProto: http://www.pcb-proto.com/ (very large pool)
○ JackAltac: http://www.jackaltac.com/ (cheaper one)
● Components (need Bill of Material):
○ Farnell, RS, Futura...
● Assembly (in case of pick-and-place need module position files)
○ Md srl is now providing an assembly service (quite expensive for
small numbers)
○ ...otherwise buy a solder station

GPIO - General Purpose In/Out
● GPIO strip provides different communication
layers (board to board or on single board)
○ Generic In/Out pins (different libraries)
○ UART - Serial Communication
○ I2C - InterIntegrated Circuit
○ SPI - Serial Peripheral Interface

GPIO - Support Libraries
● Not included by default
○ http://www.airspayce.com/mikem/bcm2835/bcm2835-1.37.tar.gz
./configure
make
sudo make check
sudo make install

int main(void)
{
if (!bcm2835_init()) { exit(1); }
bcm2835_gpio_fsel(RPI_V2_GPIO_P1_11, BCM2835_GPIO_FSEL_OUTP);
bcm2835_gpio_write(RPI_V2_GPIO_P1_11, HIGH);
return 0;
}

int main(void)
{
if (!bcm2835_init()) { exit(1); }
uint8_t c = 0;
while (1) {
bcm2835_gpio_write(RPI_V2_GPIO_P1_11, c);
c = !c;
sleep(1);
}
return 0;
}

GPIO - BCM2835 - board versions
● Model A
○ RPI_GPIO_P1_03
○ RPI_GPIO_P1_05
○ RPI_GPIO_P1_07
● Model B
○ RPI_V2_GPIO_P1_03
● Model B+
RPI_BPLUS_GPIO_J8_03
http://www.airspayce.com/mikem/bcm2835/bcm2835_8h_source.html

GPIO in action
Low-cost ultrasonic
sensors turn on/off a
pin in order to convert
real distances
HC-SR04
https://github.com/wdalmut/libultrasonic

UART for Raspberry Pi
● 2 functional modes
○ TTY for terminal connections (serial console)
○ For other micros and components
● Peripheral mode need few configurations
○ Appears as /dev/ttyAMA0
○ http://elinux.
org/RPi_Serial_Connection#Connection_to_a_micro
controller_or_other_peripheral

Initialize your serial module
void serial_init(void)
{
uart0_filestream = open(“/dev/ttyAMA0”, O_RDWR | O_NOCTTY |
O_NDELAY);
if (uart0_filestream == -1)
{
//TODO error handling...
}
}

Config your UART registry
void serial_config(void)
{
struct termios options;
tcgetattr(uart0_filestream, &options);
options.c_cflag = B9600 | CS8 | CLOCAL | CREAD;
options.c_iflag = IGNPAR;
options.c_oflag = 0;
options.c_lflag = 0;
tcflush(uart0_filestream, TCIFLUSH);
tcsetattr(uart0_filestream, TCSANOW, &options);
}

Send data to your peripheral
int count = write(uart0_filestream, data, dataLen);
Pay attention with strings (char vectors) because dataLen doesn’t
include the termination byte (“0”)

Read data from your peripheral
int rx_length = read(uart0_filestream, (void*)(&c), len);

A navigation shield for Raspberry Pi
Adafruit Ultimate GPS
Breakout v3
UART GPS module
https://github.com/wdalmut/libgps

I2C - Inter-Integrated Circuit
● Multiple components uses I2C in order to
communicate
● Raspberry PI supports also this peripherals
as a master node
● On raspberry the I2C is disabled by default,
you have to enable it!
○ Enable it in your: /etc/modprobe.d/raspi-blacklist.
conf

I2C - Initialize it
void mma7660fc_init(void)
{
i2cdev = open(“/dev/i2c-1”, O_RDWR);
if (i2cdev == -1)
{
//TODO handle errors
}
}

I2C - Write and control your slaves!
void mma7660fc_on(void)
{
uint8_t buffer[2];
buffer[0] = MMA7660_MODE;
buffer[1] = MMA7660_ACTIVE;
ioctl(i2cdev, I2C_SLAVE, MMA7660_ADDR);
write(i2cdev, buffer, 2);
}

Read from your slaves
void mma7660fc_get(accel_t *data)
{
uint8_t buffer[11];
ioctl(i2cdev, I2C_SLAVE, MMA7660_ADDR);
read(i2cdev, buffer, 3); //only x,y,z
data->x = mma7660fc_convert(buffer[0]);
data->y = mma7660fc_convert(buffer[1]);
data->z = mma7660fc_convert(buffer[2]);
}

i2c in action
MMA7660
● 3-axis accelerometer
● Tilt detection
● Movement detection
https://github.com/wdalmut/libimu

Higher level with Golang
package gps
import(
// #cgo LDFLAGS: -lgps -lm
// #include <gps.h>
"C"
)
func GpsLocation() (float64, float64) {
var data C.loc_t
var lat, lon float64
C.gps_location(&data)
lat = float64(data.latitude)
lon = float64(data.longitude)
return lat, lon
}

Any question?
Thanks for listening

Raspberry Pi - HW/SW Application Development

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