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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 siliconchip.com.au Silicon Chip Binders REAL VALUE AT $12.95 PLUS P & P These binders will protect your copies of S ILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold 12 issues & will look great on your bookshelf. 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. siliconchip.com.au H SILICON CHIP logo printed in gold-coloured lettering on spine & cover H Buy five and get them postage free! Price: $A12.95 plus $A7 p&p per order. Available only in Aust. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Use this handy form Enclosed is my cheque/money order for $________ or please debit my  Bankcard  Visa    Mastercard Card No: _________________________________ Card Expiry Date ____/____ 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 siliconchip.com.au 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