Low-power LCD is... hard!

A project log for LCD Solar Creatures

Solar-powered creatures that react to energy with animations on a 7-segment LCD. And they blink at night!

gaborGabor 06/12/2022 at 11:420 Comments

Simple, 7-segment monochrome LCDs have been on every cheap calculator and digital wrist watch for decades, so you'd think they are the easiest component to find for a low-power electronics project... But they are not! In reality, this has probably been the part of where I spent the most time looking for a solution.

There is no shortage of easy-to-use display modules for microntrollers if you're looking for an OLED display or even a 7-segment LED display. These are fun, but they are definitely not low-power.

Then there is an abundance of bare-bones LCD displays without a driver. These are parts with lots and lots of connectors, looking a little something like this:

They are cheap, readily available - and a real pain to use. It's not just the sheer number of wires, though that's an issue as well. The problem with an LCD is that you cannot just send power to the right pins and hope for things to work out. You need to actively send alternatig signals to prevent irreversible chemical changes inside. People have done it before and written about it, and it makes for a really interesting read too: Driving an LCD display directly with ATtiny. But I'm not ready to bikeshed this from scratch.

And I don't need to, either: there are ready-made components to drive an LCD. After a great deal of searching I zoomed in on the HT1621, which seems to be the most widely used one for small displays with up to 32 segments. I could get one of these and hook it up with a bare-bones LCD display, except... The HT1621 has a lot of pins, and it comes in an extremely tiny form factor. Just to get started I would need to get a custom PCB manufactured, and I'm pretty convinced I wouldn't even be able to solder parts this small. I need a breakout board.

Which is where things get really, really difficult. It's exactly these breakout boards that seem to barely exist. Mohit Bhoite has apparently found one for his latest satellite, but it's unclear where it comes from. Maybe it's this part from Hexpert systems? There's something inside me that rebels against spending 12 bucks on what's supposed to be a super simple mass-produced component. [UPDATE: Mohit just tweeted about this, and it's exactly as I thought: his satellite uses the part from Hexpert.]

And so I turned to Aliexpress, where I eventually struck gold. The link will most likely be gone soon, so here's a screenshot of my bounty:

44€ might sound like a lot, but it's for a bag of 10, and I think when I placed my order it was more like 30€. Anyway, these postings come and go all the time and the price of the exact same product varies a lot, so it's worth searching around!

I placed my order, crossed my fingers, and waited... And true enough, in about four weeks I had a padded envelope in my mailbox with a literal bag of 10 of these things.

NOW the fun can start! But that will be a separate update.

Useful links: