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The expansion boards connect to the AVR200 via its
I2C bus connector. Most expansion boards have two
bus connectors, allowing them to be daisy chained. The
AVR212 and AVR213 boards shown here provide eight
additional outputs and inputs, respectively.
Six low-cost
E x pan sion Board s
for the AVR200
Add up to 128 bits of digital I/O, a keypad and LCD, more
non-volatile memory – or a combination of any of these for
a very reasonable price.
By PETER SMITH
B
ACK IN JUNE AND JULY 2005,
we described a low-cost, highperformance development board from
JED Microprocessors based on the
popular ATmega32 microcontroller.
Since then, JED have produced a
complete range of add-on modules
for the AVR200, most of which can be
purchased in kit form.
Included in the range are prototype,
I/O expansion, non-volatile memory,
keypad and LCD interface boards.
All boards communicate via the I2C
(TWI) serial bus, with the prototype
and memory boards plugging directly
into the AVR200’s “upstairs” connector (J14).
All other boards connect via the
AVR200’s 10-way I2C header (J6) and
use the Philips 82B715 bus extender IC
for communication at up to 100m (at
44 Silicon Chip
the 71kHz data rate) from the AVR200
using ordinary ribbon cable. Note that
as the I2C bus frequency is reduced
this distance will increase; refer to
the Philips application note AN10216
(available from www.semiconductors.
philips.com) for specific details.
All remote boards are based around
the PCF8574 or PCF8574A 8-bit I/O
expander IC. Essentially, these ICs act
as addressable nodes with eight input/
output lines. Most boards include
two I2C headers, allowing subsequent
boards to be wired together in daisychain fashion. This makes for a truly
simple and flexible expansion system.
Let’s look at each board in a little more
detail.
AVR201 I2C FRAM board
Up to eight FM24C256 chips can
be installed on the AVR201 for a total
of 256Kbytes of non-volatile memory.
Alternatively, the board can be ordered
with one, two or four chips for a total
of 32, 64 or 128Kbytes of memory,
respectively.
The FM24C256 is a ferroelectric
random access memory (FRAM) device with a read/write endurance of at
least 10 billion cycles, no write delays
and data retention for at least 10 years.
Individual memory chips can be
hardware write-protected by installing
jumpers on the board.
Input power requirements are 5V
DC at 800mA (idle), increasing to about
1.2mA during read/write access. As
mentioned earlier, the AVR201 plugs
directly into the “upstairs” connector (J14) on the AVR200, as does the
AVR202 prototyping board, so these
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The AVR202 prototype board
makes it easy to assemble and test
experimental circuits. It mounts
directly above the AVR200 board.
two don’t readily co-exist.
Note that as the FM24C256 memory
chips are only available in surfacemount packages, JED has elected to
offer the AVR201 in preassembled
form only. This eliminates the hassle of
soldering these subminiature devices
by hand.
AVR202 prototype board
Experimental circuits can be conveniently built and connected to the
AVR200 using the prototyping board.
This board plugs into “upstairs” connectors J13 & J14, which provide access to both the I2C and SPI buses, as
well as several bits of Port B.
The board mounts in satellite fashion directly above the AVR200 and is
secured to it by four tapped spacers
and screws. Included on the board is
space for six decoupling capacitors,
four LEDs and their current-limiting
resistors, and four 5-way screw-terminal blocks. The remainder of the board
is laid out with a large array of platedthrough holes on a 0.1-inch grid, just
waiting for your next invention!
In addition, it supports the latest
PLED (polymer-based LED) displays
that are compatible with the older
LCD technology. Compared to backlit
LCD modules, these have the advantages of lower power consumption and
brighter displays with wider viewing
angles. Various linking options and
resistor values allow for minor variances between the two display types
and backlighting options. For example, the on-board potentiometer can
be set to control either LCD contrast
or PLED brilliance.
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AVR210 I2C LCD board
Adding a liquid crystal display
to the AVR200 becomes a relatively
simple task with the aid of an AVR210.
This board works with any alphanumeric LCD that uses an integrated
HD44780 or compatible controller.
H 80mm internal width
Signature ________________________
The KEY200A
16-key stick-down
keypad features
“user-loadable
lettering”.
Name ____________________________
Address__________________________
__________________ P/code_______
March 2006 45
Both single and dual-row header
display types can be accommodated,
due in part to the small size of the
AVR210 as well as its mounting
method. Basically, it’s attached to the
rear of the chosen display module
via the header and several layers of
double-sided tape.
Backlighting is software controllable and can be powered either by
the I2C bus or a separate DC power
source, depending on current requirements. For an AVR210 equipped with
an LCD (no backlighting), the board
draws about 20mA at 5V. However, for
a large 4 x 20 LCD with LED backlighting, this requirement could increase to
over 180mA.
Interestingly, this board and the
AVR211 keypad interface can be built
as buffered or non-buffered I2C peripherals. For the non-buffered builds,
the main omission is the 82B715 bus
extender chip, presumably to cut costs
in short distance I2C bus hook-up
schemes.
AVR211 I2C keypad board
The AVR210 easily attaches directly to the rear of most alphanumeric LCD or
PLED modules. Most modules can be powered from the I2C bus or an external
supply can be connected for units with high-current LED backlights.
Need a keypad to complete your
front-panel interface? JED has this
angle covered too with their AVR211
keypad interface board.
This board allows the AVR200 to
read up to 16 individual push-button
switches wired in a 4 x 4 matrix. Continual switch polling is unnecessary,
as the PCF8574’s interrupt pin can be
programmed to signal when a switch
closure takes place.
If you need a keypad rather than individual switches, then JED offers the
KEY200A 16-key stick-down keypad
with “user-loadable lettering”. A keypad can be customised and mounted
ready for use in just a few minutes
with this system.
As with all other boards, the AVR-211 receives its regulated 5V supply
from the AVR200 via the I2C bus cable.
Typical supply current is a respectable
20mA.
AVR212 I2C output board
This “Floribots” interactive kinetic sculpture is powered by a single-board
computer with similar capabilities to the AVR200. It was created by Geoffrey
Drake-Brockman and was short-listed for the 2005 National Sculpture prize.
Specifically, Floribots incorporates a JED573 microcontroller board, which is
similar to the AVR200 but incorporates an ATmega128 micro. Sixteen AVR212
output boards drive the sculpture. The whole shebang runs a compiled BASIC
program and monitors the outside world via eight infrared sensors. More details
can be found on the JED website at www.jedmicro.com.au/avr200.htm.
46 Silicon Chip
This board allows you to add eight
more digital outputs to the AVR200.
It features high-current open-drain
Mosfet outputs, with the state of each
output displayed by a rectangular
green LED.
Although the supplied Mosfets are
capable of sinking greater than 10A
continuous current, the maximum
safe current level is determined by the
siliconchip.com.au
The guys at JED recently needed a jig for testing wiring harnesses, and
their solution was (not surprisingly) an AVR200 with lots of extra I/O. As
shown here, the end result was stuffed with four AVR212 output boards,
eight AVR213 input boards and the whole lot mounted on a wooden
backing board! The test software was written in BASIC for the BASCOM
compiler. JED will supply the code to anyone interested in seeing how it
was all done.
AVR212’s PC board track width. In this
case, ground current must be limited
to 4A per group of four Mosfets or 1A
per Mosfet.
Like the AVR213 input board (see
below), the AVR212 has eight possible address configurations, selectable
with on-board jumpers. The on-board
PCF8574 and PCF8574A I/O expander
chips occupy two different address
ranges, so up to 16 unique addresses
are achievable by using both device
variants. This means that up to 16
input/output boards can be installed
on one I2C bus for 128 individual I/O
lines.
In standby mode with no LEDs illuminated, the AVR212 draws a maximum of 15mA at 5V. With all LEDs lit,
this will increase to approximately
60mA.
AVR213 I2C input board
The AVR200’s digital input capability is readily expanded with the aid of
an AVR213 input board. These boards
have eight general-purpose inputs, all
of which are over-voltage protected.
Inputs can be pulled up to 5V or down
to ground simply by repositioning two
plug-in resistor packs.
The state of all bits is made visible
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via a row of rectangular red LEDs.
In addition, the AVR213 can be programmed to generate an interrupt
whenever an input changes state.
Note, however, that only two interrupt
lines are available on the AVR200’s
I2C bus, which may limit this feature
when using multiple boards. In some
applications, it would be possible to
share interrupt lines between boards,
as the PCF8574’s interrupt output is
open drain.
In standby mode with no LEDs illuminated, the AVR213 draws a maximum of 15mA at 5V. With all LEDs lit,
this will increase to approximately
60mA.
Software
Most of the I2C boards described
here are supplied with demonstration programs written in C for the
CodeVision AVR C compiler. These
can be used to test the boards as well
as gain an insight into how to access
their various elements from within
your own code.
What’s coming?
JED Microprocessors is currently
working on more I2C expansion boards
for the AVR200, including a multiple
This is the AVR201 FRAM board with
all eight FM24C256 chips installed for
256kbytes of non-volatile memory.
The AVR211 keypad interface board
allows the AVR200 to read up to 16
keys in a 4 x 4 matrix.
servo actuator driver and an 8-bit
power relay board. Need something
special? The engineers at JED are always ready for a new challenge – give
them a call!
Pricing and technical details for
the complete range of I2C expansion
boards can be obtained from www.
jedmicro.com.au/avr200.htm. You
can reach JED Microprocessors on
(03) 9762 3588 or via email at jed<at>
SC
jedmicro.com.au
March 2006 47
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