Display circuit

Posted on Feb 7, 2014

Had bought this EDE702 some time ago, and a LED-backlit LCD character display. After buying the EDE702, I considered that it did not provide enough integration with HD44780-compatible displays to justify its price. Nevertheless I should use it, as it would be more use set up than lying in a box. It was convenient to put it in the Secure DigitalWriter box, as there was room for the display, and the

Display circuit
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serial infrastructure already was in it. However, the display and the writer are not compatible, since they require different commands. Although the existing board has enough space for the EDE702, it was put on a separate board because of the large number of connections to the display. The display board plugs directly into the display with a single-row header. I was not sure how much current the LED backlight should have, since I did not have a data sheet which matched the marking on the display, and it did not have a dropping resistor. A data sheet for a similar-appearing display gave 240 mA for the backlight, but this seemed excessive, so after experimenting I chose 80 MA, which did require rework of the writer board to put a heatsink on the regulator. This display is black on yellow, and is very readable indoors, with a good field of view.

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