I debated whether or not I should add to this thread given its age but it seems to have recent traffic so...
This post might be a bit long. Even if nobody reads it, it was kind of therapeutic to write it.
Way back in this thread there was talk about replacing the OLED in this meter with an LCD. I think the talk at the time was about replacing it with a fixed-segment display. I didn't have one of those, but I still wondered what the U1253A would look like with a graphic LCD and sort of became obsessed with having one. This is what I wound up with:
The display looks slightly washed out in that pic for some reason, the contrast is better in person. This works because the memory organization and the relevant commands sent by the U1253 (the address-related commands) are basically 1:1 between OLED and LCD graphics modules. I just suppress all the other commands and give the LCD the initialization commands it needs at boot time. I also intercept the OLED brightness command and use it to set the duty on a PWM output, so I can use it as backlight brightness. I don't have any way to set contrast. I picked a middle-of-the-road value that works pretty well when the meter in its normal place on my bench, and hard-coded it in software.
Some might be wondering, the current drawn is as follows:
Condition: Vbatt = 8V
Backlight high: 32mA
Backlight medium: 25mA
Backlight low: 20mA
I have the meter configured to start at medium. I don't remember what the original OLED drew, but nobody ever bought this meter for its battery life so
.
Aside from flipping the power lines to the LCD in my PCB and having to do some surgery to recover from it, I'm happy with this build. I had fun doing it and I think the display I picked looks at home in the case.
Having said that I'm not sure I'd run out and tell anyone else to do this. There were issues:
1. The display update rate of this meter is pretty fast. The display has a hard time keeping up when the numbers jump around. In practice I'm probably not using those numbers for anything when they are jumping around but it's not as crisp as the OLED was with the fast updates. Once the reading settles, the numbers look fine. The glass I used here is STN, I think maybe a FSTN display would have worked better, but I could not find one to meet my display area and overall size requirements.
2. These graphic LCDs are big. I used this one:
https://www.buydisplay.com/blue-2-6-inch-128x64-cog-lcd-module-display-with-touch-panel-serial-spi. It was the sweet spot between display area and overall size. I spent a lot of time looking at spec sheets to settle on this one. It seems that graphic LCDs for a given display area run much larger overall than a similar OLED. This module mostly covers the area of the original display board used in the U1253A. More than that, these modules are much thicker mostly due to the backlight. The one I used has a spec of max thickness of 5mm. My actual display is about 4.8mm thick. For the display are, this is about the thinnest I could find. the OLED I think was less than 1/2 that thickness. The physical reality of the display module had a ripple effect into everything.
You have about 11.2mm total height off the board for everything before you start having issues putting the case back together. The full stack with the original standoffs and the original board lands you at about 8.25mm. Add the LCD to that and you are over 13mm. I ultimately had to gut all the old mounting, including the connector on the board and redo all of it to fit the new module into the envelope I had. It's actually worse, because the screws that hold the board on are on the top of the board, and the display is so large it will sit on top of them.
Here is a side view of the final stack-up fully assembled:
From the U1253 board up:
1. .8mm board with the new interface stuff on it (the connector on the side is the ICSP connector. I had these connectors laying around and I did not care that it had more pins than I needed.
2. 3d printed mounting plate. This plate has standoffs integrated in it so that the top surface can be completely flat. I just printed them so that I could press-fit some metal standoffs into it to accept the screws which come in from the bottom of the U1253A board.
3. The LCD itself
Additionally you might notice the ribbon cable from the LCD comes out the top, the original OLED was on the bottom. The need to route this cable, combined with the fact that the old connector was too high off the board anyhow, meant I needed a new way to connect the display board to the main board. Ultimately I used a flat-flex cable to do this. I had to make an adapter board to convert the old footprint for the 2mm rectangular connector to a 20-pin FFC connector.
The little adapter board is also .8mm thick. JLC does these for their standard prototype pricing and timelines which is pretty amazing. This board was a total PITA to route, I spent more time routing this board than I did the main board. Doing this allows me to get the connector out of the way, so the FPC connector on the LCD can wrap around.
I have a couple more pics, I will add them in a second post.
Home
Help
Search
Login
Register
