2 Line by 16 Character LCD Add-On Circuit
The Dragon Rider printed circuit board includes an area for a 2 Line by 16 Character LCD module and support circuits. A 10-pin header allows the LCD to be linked to a target microcontroller port with a 10-way ribbon cable of the type supplied with the Atmel STK500. The module uses the very common HD44780-type controller, wired in 4-bit mode to conserve port bits. Firm support is provided by standoffs and the display contrast can be adjusted with a trimmer potentiometer.
Typical Parts Required
The table below lists the parts that are provided in the ECROS Technology add-on parts kit for the LCD. Although you will need the exact specified LCD module (for a mechanical fit), many of the other parts are not critical and are the sort of thing you may have in your spares drawer. The comments column should help you find substitutes; refer also to the Technical Information section, below.
|1||10-pin headers (2 by 5)||J31||Common 0.1 in. pin spacing|
|1||2 line by 16 character LCD||LCD1||Lumex LCM-S01602DTR/M|
|1||1-row by 14-pin header †||-||Mount to Dragon Rider at LCD1|
|1||1-row by 14-pin header socket †||-||Mount to LCD module|
|2||Pillars, 6-32, 0.375 in. nylon||-||0.437 in. would be better|
|2||Hex nuts, 6-32, nylon||-||.|
|2||Washers, #6, 0.062 in. thick, nylon||-||Used to increase pillar height|
|2||Machine screws, 6-32, pan head, nylon||-||Used to secure LCD, steel screws OK|
|1||2 kohm resistor||R7||Logic pull-down, value not critical|
|1||10 kohm resistor||R8||Value not critical, 5 to 15 kohm OK|
|1||5 kohm trimmer||R9||LCD "contrast" adjustment|
† Headers and sockets with more pins can be snapped or cut to size.
Click here to open a window with the schematic of this add-on circuit.
The LCD circuit is independent of all other circuitry on the Dragon Rider, having only the ground connection in common. Power is taken from pin 10 of header J31. Therefore, the LCD can be connected to and used with other systems, for example the Atmel STK500. This is possible whether or not the Dragon Rider is powered or in use with the Dragon.
The upper four bits of the LCD module's HD44780-type controller are connected to pins 5 to 8 of J31, so when connected to a port header (such as J4 for Port D) they appear at the corresponding bits, i.e. 4 to 7. The register select (RS) line is connected to pin 4 and so appears at bit 3. The enable (E) line is connected to pin 3 and so appears at bit 2. The read/write (R/W) line is brought to a pad and can be linked with a wire jumper to pin 2, so appearing at bit 1 of the port, or can be linked to a pull-down resistor, R7, so that the controller is operated in write-only mode. Not being able to read from the controller means implementing timed, worst-case delays in software (rather than polling a status bit), but conserves a port bit.
The trimmer potentiometer, R9, allows the "contrast" of the LCD to be adjusted for best appearance. The specified LCD module needs a nominal 5 volt supply, so this circuit should not be used when the target voltage is below 4.5 volts. A direct connection to power supplied by the AVR Dragon is fine.