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 number of chips down for some actual hands-on reverse engineering.
“I received a maintain of a whole lot of these 1×32 LCD shows, however I could not discover a datasheet for them,” Chandra writes by means of background to the undertaking. “They did not appear significantly attention-grabbing at first, however throwing out 150+ of them appeared like an enormous waste. I noticed later that I could not discover one other instance of a 1×32 LCD show anyplace 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 — except for the producer’s web site, which listed a variety of different shows however no single-line units like these. Inspecting the board had an additional problem: the driving force used a chip-on-board (COB) development, overlaying the half in a thick blob of opaque black epoxy.
“The datasheets of the same shows did embody the driving force chip they used, the ST7066,” Chandra notes. “Wanting on the ST7066’s datasheet I noticed that the required exterior parts is also discovered on my show’s PCB. I used to be capable of verify with a multimeter that they had been linked in the identical means 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 work out the pinout that means,” Chandra says. “However I had by no means performed this earlier than. I additionally haven’t got 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 all the pieces in a landfill. (📷: Sudhir Chandra)
In order that’s precisely what Chandra did. Whereas sanding the epoxy blob down, Chandra realised one thing apart from the ST7066 have to 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 affordable microscope from a closed veterinary clinic and modifying it with a brand new mild supply, he switched to utilizing a warmth gun and a passion 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 hearth 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 discovered 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 complete 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.
