Custard pi 7 user information

CUSTARD PI 7
USER INFORMATION
The Industrial Control Interface for the Raspberry Pi
9th November 2014
SF Innovations

www.sf-innovations.co.uk
OVERVIEW OF FEATURES
2 Relay outputs
4 Open Collector outputs
2 Built in Switches
8 General Purpose Digital I/O
4 Analogue inputs
1 Analogue output
16 pin LCD Interface
LED indication on most ports
Screw terminal connection on most ports
Flexible Power Supply
Board can be powered from Raspberry Pi
Board and Rpi can be powered from 5V supply
Board and Rpi can be powered by 2 separate 5V supplies
LED indication of 5VPi, 5V and 3V3 supplies
Fused 5V and 3V3 available on screw terminals
Prototyping area with pads for 14-pin SMT IC
Ribbon Connector (26 way) to the Raspberry Pi GPIO
Second Connector (26 way) to daisy chain a second Custard Pi -7

LAYOUT OF COMPONENTS
This PCB board size 15cm x 11 cm

PROTOTYPING AREA

RELAY AND OPEN COLLECTOR OUTPUTS
This is provided using the MCP23008 8-port I/O expander which works
on the I2C bus.
This is followed by the Darlington Driver, the ULN2801 which drives the
relays and provides the 4 Open Collector Outputs. There are 6 LEDs
which indicate the status of these outputs.
The 2 spare pins of the MCP23008 are used for the 2 key inputs from the
on board switches.

These are shown on the picture below. There are 2 sets of screw
terminals provided with the relays with access to the 3 terminals
(common, normally closed and normally open) of each relay. Screw
terminals are also provided for the 4 Open Collector outputs and the 2
keypad inputs.

on the I2C bus.
This is followed by the Darlington Driver, the ULN2801 which drives the
relays and provides the 4 Open Collector Outputs. There are 6 LEDs
which indicate the status of these outputs.
The 2 spare pins of the MCP23008 are used for the 2 key inputs from the
on board switches.
The functions to control these are provided in cpi7x.py. Download from
here and change from .txt to .py.
Default I2C address is 0x27 (add7)
The 4 Open Collector outputs are switched on and off using the following
settings.
ONoc1 and OFFoc1, ONoc2 and OFFoc2, ONoc3 and OFFoc3, ONoc4
and OFFoc4

The 2 relays are switched on and off using the following settings.
ONrl1 and OFFrl1, ONrl2 and OFFrl2.
The actual function to set them ON and OFF is:
setbit (address , setting) & clrbit (address, setting)
In readbit (address, bit) function allows the user to read the status of the
the 2 keypad inputs.
In addition the setinandout (address) function sets the MCP23008 chip to
use 6 of the pins as outputs and 2 as inputs.

#1/usr/bin/env python
import time
import cpi7x
#start program
board1=cpi7x.add7
cpi7x.setinandout(board1)
cpi7x.alloff(board1)
while True:
cpi7x.setbit(board1, cpi7x.ONoc1)
time.sleep (0.2)
time.sleep (0.2)
time.sleep (0.2)
time.sleep (0.2)
cpi7x.setbit(board1, cpi7x.ONrl2)
time.sleep (0.2)
cpi7x.setbit(board1, cpi7x.ONrl1)
time.sleep (0.5)
Listing of sample
program to switch relays
and open collector
outputs on and off and
read keypad inputs.
Download from here and
change from .txt to .py
Cpi7ocrelkp.py

cpi7x.clrbit(board1, cpi7x.OFFoc1)
cpi7x.clrbit(board1, cpi7x.OFFrl2)
cpi7x.clrbit(board1, cpi7x.OFFrl1)
time.sleep (0.5)
kp2 = (cpi7x.readbit (board1, 0x01))
kp1 = (cpi7x.readbit (board1, 0x02))
if kp1 == 0:
print "kp1 pressed"
if kp2 == 0:
print "kp2 pressed"
import sys
sys.exit()

LCD INTERFACE
This is provided using the
MCP23008 8-port I/O expander
which works on the I2C bus (default
address 0x25)
A 2 x 16 character display has a
16pin connector on a 0.1 inch pitch
and can easily be connected to the
Custard Pi 7 with a ribbon connector.
The functions to drive the display are
provided in cpi7lcd.py. Download
from here and change from .txt to
.py.

LCD INTERFACE
Here is a ribbon cable connecting the LCD to the Custard Pi 7. (You will
need to solder a 16 way connector to the LCD.)

LCD INTERFACE
import time
import cpi7lcd
lcd = cpi7lcd
lcd.lcdinit(0x25)
while True:
lcd.lcd_clear
time.sleep (0.5)
lcd.lcd_puts("LCD line 1 test",1) #display text on line 1
time.sleep (0.5)
lcd.lcd_clear
lcd.lcd_puts("LCD line 2 test",2) #display text on line 2
time.sleep (0.5)
lcd.lcdinit(0x25)
import sys
sys.exit()
Listing of sample
program to write to a 2
line display.
testlcd.py

8 GENERAL PURPOSE DIGITAL I/O
on the I2C bus (default address 0x26).
The functions to control these I/O is provided in cpi7y.py. Download from

The functions to control these I/O is provided in cpi7y.py. Download from
This works very similarly to the Relay and Open Collector controls. For
this example 4 of the bits are set as outputs and 4 as inputs.
The settings to control the outputs are:
ONbit4, ONbit5, ONbit6, ONbit7 and OFFbit4, OFFbit5, OFFbit6,
OFFbit7.
The functions available are:
setbit To switch outputs high
clrbit To switch outputs low
readbit Read inputs
setinandout To set 4 bits as outputs and 4 as inputs
setpullups 100k pullups on input pins
alloff set all outputs to lo

The MCP23008 is a very versatile input output device. It allows the user set
All 8 pins as inputs, outputs or a mix of inputs and outputs. The inputs can be
set to have pull-ups and also generate an interrupt on change of status.
There is more info on the registers on the datasheet.

import time
import cpi7y
import pylcdlibseg
board1=cpi7y.add6
cpi7y.setinandout(board1)
cpi7y.setpullups(board1)
cpi7y.alloff(board1)
while True:
cpi7y.setbit(board1, cpi7y.ONbit4)
time.sleep (0.2)
time.sleep (0.2)
time.sleep (0.2)
time.sleep (0.5)
cpi7y.clrbit(board1, cpi7y.OFFbit4)
time.sleep (0.5)
Listing of sample program to
switch the 4 outputs high and
low and read the 4 inputs.
Cpi7gpio.py
To test:
Connect a resistor and LED
from bit4 to GND and see it
flash. Then test bit5, bit6 and
bit7.

bit0 = (cpi7y.readbit (board1, 0x01))
if bit0 == 0:
print "bit0 low"
else:
print "bit0 high“
if bit1 == 0:
print "bit1 low"
else:
print "bit1 high“
if bit2 == 0:
print "bit2 low"
else:
print "bit2 high“
if bit3 == 0:
print "bit3 low"
else:
print "bit3 high"
print "***************************"
import sys
sys.exit()
To test:
Connect a link from bit0 to
GND and check that the
program detects this. Then
test bit3, bit2 and bit 1.

4 ANALOGUE INPUTS AND ANALOGUE OUTPUT
This is provided using the PCF8591 8-bit A to D D to A convertor which
works on the I2C bus (default address 0x4F).

import time
import smbus
#********************************************
# Custard Pi 7 8591 25th Oct 2013
#I2C addresses
add= 0x4F
bus=smbus.SMBus(1)
#DtoA channel select
ch0= 0x00
ch1= 0x01
ch2= 0x02
ch3= 0x03
def readanalog(add):
analog=bus.read_byte(add)
return analog
def writedtoa(add,value):
bus.write_byte_data (add, 0x44, value)
#******************************************
Listing of sample program to
output an analogue voltage
and read the voltage on the 4
analogue inputs.
cp8591.py
To test:
Loop back the ANOUT back
to ANIN0, ANIN1 etc in turn
and see that the analogue
output is being read
correctly.

while True:
value=0x00
for x in range (0,255):
writedtoa(add,value)
print value
time.sleep(0.5)
value=value+1
an0 = readanalog(add)
print "ch0=", (an0)
print "ch1=", (an1)
print "ch2=", (an2)
print "ch3=", (an3)
print "*****“
time.sleep(0.5)

POWER MANAGEMENT
There are 3 powering options.
#1 The Rpi and the Custard Pi 7 can both
be powered from the Rpi 5V supply. In this
case jumper J14 is on the left hand side
and the board 5V and the Rpi 5VPI are
both connected together. Make sure that
only the Rpi 5V supply is connected.
#2 Both can be powered from the board
5V. Same as above but make sure that
only the board 5V is plugged in.
#3 Both are independently powered. In this
case make sure that jumper on J14 is on
right hand side (or not plugged in).

POWER CONNECTORS
There is a 3-way ground connector provided.
The 3V3 and 5V supply outputs on the screw terminal are fused at 100mA
to prevent users from taking too much power from these rails.

MULTIPLE CUSTARD PI 7 BOARDS
Because the Custard Pi 7 uses the I2C interface to interface to the various
functional blocks it is possible to daisychaining 2 or more Custard Pi 7s.
The user has to pay attention to the I2C addressing to make sure that the
devices on the various cards have different I2C addresses. There are also
resistor positions available on the PCB to do this.
One needs to pay particular attention to the power requirements.

SETTING UP THE I2C BUS – STEP 1
At the command prompt type:
sudo nano /etc/modules
This uses the nano editor to make some changes to the modules file.
Add the following two lines to this file
i2c-bcm2708
i2c-dev
Then save and exit the file using CTRL-x and Y.

Make sure that you have the I2C utilities installed by executing the
following two commands. The Pi will need to be connected to the Internet
for this.
sudo apt-get install python-smbus
sudo apt-get install i2c-tools
If you get a 404 error do an update first:
sudo apt-get update
Note : The installation could take a few minutes to do, depend on how
busy the server is.
Now add a new user to the i2c group:
sudo adduser pi i2c

On the Raspberry Pi, the I2C and the SPI buses are usually disabled.
This is done in the /etc/modprobe.d/raspi-blacklist.conf file.
If this file is not present then there is nothing to be done. Otherwise edit
the file by typing the following at the command prompt.
sudo nano /etc/modprobe.d/raspi-blacklist.conf
If the I2C and the SPI is blacklisted, you will see the following commands.
blacklist spi-bcm2708
blacklist i2c-bcm2708
Insert a # in front of these to comment them out.
Then save and exit the file using CTRL-x and Y.
After editing the file, you will need to reboot for the changes to take
effect.

Now we need to test if the I2C bus is working correctly.
Connect up the Custard Pi 6 board (or any other I2C bus device) and run
the following command.
sudo i2cdetect -y 1 (for Rev 2 boards which uses port 1)
Or
sudo i2cdetect -y 0 (for Rev 1 boards which uses port 0)
If everything is OK, then the I2C address of the device will be shown as
on the following slide.

I2C devices with address 40 and 70 present on the bus.

SUMMARY
The Custard Pi 7 provides Raspberry Pi hardware hackers with a handy
board that is packed with features.
Make sure you refer to the www.sf-innovations.co.uk website for the latest
user information.
Further information
Blog dedicated to electronics & Raspberry Pi

Custard pi 7 user information

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