I really like the
Adafruit LCD Backpack, but I've been wanting to play around with adjusting the LCD backlight brightness programatically. After much mulling and reading of forum posts, I decided to just operate the backlight using one extra wire to a PWM pin on the Arduino. To try and keep things tidy, I ordered some extra
3-pin terminal blocks so I could make a 6-pin block instead of the normal 5-pin block. Just to up the stakes, I'm doing this with my brand new
20x4 LCD.
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All the Bits and Pieces |
First up, I broke off 15 header pins instead of 16 and soldered them into openings 1-15, leaving opening 16 empty; this is labeled "K" on my LCD. According to the
tutorial at Adafruit, this is the backlight ground connection. I then cut a length of wire, stripped one end and soldered it through opening 16.
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Backpack with Pins and Wire Soldered |
I "folded" over the wire end and soldered it to the pad on the LCD. This required a little bit of finagling with my third hand's alligator clips, but wasn't too rough.
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Backlight Ground Wire Soldered to LCD |
I swapped two 3-pin terminal blocks for the 2-pin and 3-pin terminal block that came with the LCD backpack
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Terminal Blocks |
I soldered the resulting 6-pin terminal block to the backpack with the extra pin overhanging the PCB on the side.
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Terminal Block Soldered in Place |
Next up was trimming the wire to fit the length of the backpack PCB and soldering it to the extra pin. This proved to be a bit of a pain, and I ended up with the LCD in a panavise, the backpack held by the third hands, a soldering iron in one hand, and needlenose pliers in the other. I'm sure there's an easier approach...
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Backlight Ground Wire Soldered to Backpack |
Finally, I soldered the regular pins in place; overall, I'm happy with the way this turned out. I am thinking of putting some insulation on the exposed extra pin / wire end.
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Finished Backpack in Place |
The code I used to test this is just the Arduino Basics/Fade example sketch and Adafruit's LiquidCrystal/HelloWorld_i2c example sketch mashed together:
Nice work, almost looks stock!
ReplyDeleteI'm somewhat surprised the Arduino can drive the LED backlight. Perhaps this module is a bit more energy efficient, but I've seen LED modules that need 100mA to light their backlight, a fair bit more than the 40mA "absolute maximum" that an Arduino can source from a single pin.
Thanks! :)
DeleteFrom the datasheet, it looks like the backlight is drawing 180mA, so that's a fair point. I was thinking that sinking the current has a higher rating; but, going back and rereading the Arduino site, I'm seeing that it's 40mA regardless of source/sink. Seems like it might be worth adding a MOSFET or transistor to the mix. Thanks for pointing that out :).
Just a quick follow up - I used my multimeter to measure the current draw, and it looks like it's fine; the most I saw was about 33mA.
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