Maker Sudhir Chandra occurred upon a big amount of single-line 32-column character shows, missing something in the way in which of documentation or drivers — so set about saving them from landfill by sanding a couple of chips down for some actual hands-on reverse engineering.
“I acquired a maintain of loads of these 1×32 LCD shows, however I could not discover a datasheet for them,” Chandra writes by means of background to the challenge. “They did not appear significantly attention-grabbing at first, however throwing out 150+ of them appeared like an enormous waste. I spotted later that I could not discover one other instance of a 1×32 LCD show wherever else, which does make them considerably distinctive.”
Sandpaper, a sizzling air gun, and a modified microscope helped to reverse engineer some uncommon single-line LCD panels. (📷: Sudhir Chandra)
Whereas the boards had been marked with half and product numbers, neither introduced up something helpful — other than the producer’s web site, which listed a spread of different shows however no single-line units like these. Inspecting the board had an additional problem: the motive force used a chip-on-board (COB) development, protecting the half in a thick blob of opaque black epoxy.
“The datasheets of the same shows did embody the motive force chip they used, the ST7066,” Chandra notes. “Trying on the ST7066’s datasheet I spotted that the required exterior elements is also discovered on my show’s PCB. I used to be capable of affirm with a multimeter that they had been related in the identical method as talked about within the datasheet.”
That was a part of the puzzle, however the show’s pinout did not match any identified ST7066-based show. “As a final resort, I might attempt to decap the chip to measure what bond wires go the place and determine the pinout that method,” Chandra says. “However I had by no means achieved this earlier than. I additionally do not have entry to nitric/sulfuric acid. Nonetheless, I did discover some movies of individuals utilizing sandpaper or a warmth gun to launch the chips from their packages.”
With 150 shows to play with, Chandra wasn’t eager to surrender and drop every little thing in a landfill. (📷: Sudhir Chandra)
In order that’s precisely what Chandra did. Whereas sanding the epoxy blob down, Chandra realised one thing aside from the ST7066 should be at play: there was solely a single chip hiding inside the blob, and the ST7066 requires a assist chip to supply greater than 16 columns. Choosing up an inexpensive microscope from a closed veterinary clinic and modifying it with a brand new gentle supply, he switched to utilizing a warmth gun and a pastime knife to unveil markings on the chip’s floor — however none had been readable with the tools at hand.
The breakthrough got here when Chandra realized the chip was much more rectangular than most driver chips, revealing it to be an ST7070. “I in contrast the measured connections of the voltage divider to the areas within the pinout of the chip within the datasheet and it appeared very promising,” he explains. “By matching these connections I might additional deduce the place all the opposite wires went. I used to be capable of hint the information bit and instruction pins to the pinout of the flat cable!”
After manually decapping a chip, Chandra constructed a brand new lighting setup for an inexpensive veterinary microscope. (📷: Sudhir Chandra)
With the Arduino LiquidCrystal library and a microcontroller wired for the weird pinout of the shows, Chandra was capable of fireplace one up for the primary time — proving his efforts weren’t in useless. To make life simpler for the remainder of the boards, Chandra used what he had realized to design a customized adapter board to carry out the show’s flat versatile circuit (FFC) cable to a breadboard-friendly 0.1″ header.
Chandra’s full write-up is accessible on his web site; he plans to write down a customized library to make it simpler to make use of the total width of the show, and is providing his spare show boards up on the market if anybody has a necessity for a 1×32 character show — an uncommon beast in today, it appears.