JEM EDP-I User Manual - Other Pinouts
Other pinouts
We have tried to address the majority of the pinouts that we’ve seen. However, there are far to
many variations for one board to cover them all. The EDP-I should be able to handle any module
that supports the pseudo-standard 7 bit interface if you can solder up the correct wires.
Backlight Current
The maximum allowable backlight current varies widely, even for modules with the same format.
For example, for different 20x2 modules, the maximum current ranges from 20 mA to 210 mA!
The EDP-I software cannot account for these variations. Therefore, the EDP-I is shipped without
a shunt on H2. This ensures that a current limiting resistor is in series with the module’s backlight
and will limit the backlight current to around 75 mA. This is still enough to damage some
modules. Check with your LCD datasheet before running the module at full brightness.
To increase the backlight current, we recommend installing a current limiting resistor at location
R14. Check with your display manufacturer for the correct value.
We highly recommend connecting an amp meter to J1, (in place of the shunt) and measuring the
actual current being drawn. IF YOUR BACKLIGHT LOOKS TOO BRIGHT, IT PROBABLY
IS! This can shorten the life of the backlight; possibly to only several seconds! Be careful!
Power
:
The EDP-I requires regulated 5VDC. An on-board connector, commonly referred to as a "P-5",
can be used (center pin is +5). The board itself uses less than 5 mA and you can figure about 350
mA for a keyboard. However, the total required is determined by the current draw of your
backlight (which is the main reason we didn't include a regulator on board). A wall mounted, 2.4
Amp switching supply is available from JEM.
Reprogramming the EDP-I
Of course, we left the 6 pin programming header on board. This allows users familiar with the
ATMEL processor to develop their own software (and you’d better be REAL familiar). Just be
careful, if you reprogram your EDP-I it is no longer an EDP-I! You will need to provide your
own keyboard interface routines and other functions as needed. We may someday release the
keyboard, contrast and backlight routines as a compiled library but they are NOT currently
available.
Of course, custom features and functions are available for an additional charge. Contact JEM
Innovation to discuss your requirements.
Spare Pins
The EDP-I provides users with access to 16 of the
processor’s I/O pins as shown. These pins are not
supported in EDP firmware and must be
programmed by the user. Refer to ATMEL
documentation for details.
Note that PD3 and PD4 are used by the Keyboard
interface.