Driving a dozen individual single element LCDs with variable amplitude - Page 1
Forum section: electronics / projects

author: DaJMasta
author_rank: Super Contributor
timestamp: January 27, 2024, 03:06:59 am
content: I got an interesting device to play with recently - a liquid crystal variable optical filter stack - that I've been able to verify basic functionality of, and I'm thinking up best ways to make driver circuitry. Basically, the connectors on the modules are just piped directly into the LCD's plates, so there is no driving built in, and both the controller and the company that made it are long gone (and seem to be sparse on the used/surplus market). For those curious, it's an older CRi Verispec module.In any case, I don't know the drive voltage for the panels, but know some drive voltages for similar devices (from a declassified military paper, no less), and know that the amplitude of the voltage across the panel needs to be adjustable - the LCD elements act as variable optical retarder plates, so being able to change it finely lets you tune the individual plate of the filter. I also know that I've got at least a dozen of these elements in the module which will need to be driven simultaneously to tune the filter correctly. From my testing, around 1kHz seems to be fine for a drive frequency (still saw some response at 500 Hz and a little at 2 kHz), and 3-5V seems to get me more variability in the transmission of a panel than is needed (from graphs in that paper, you seem to be able to get several complete polarization flips out of the normal working voltage for a panel, but that drive voltages could be up to 10V, and ebay single channel controllers suggest it could be as high as 25V on some.)So here's the quandary I'm at: what circuit would be most practical for driving all of them? While just driving everything with a bipolar DAC would be straightforward enough, it seems like overkill and way more complexity than I'd really prefer. From testing, I know that driving both plates with a square wave and then adjusting the phase between them will do what I'm looking for, but it seems like fine phase control is trickier to have an easy manual adjustment for (though I suppose the filter as a whole will probably need digital control, since tuning to a specific bandpass involves all elements). So I'm basically looking for some advice on what approach seems to be most practical/flexible/straightforward to execute. It will be a one-off for-fun project, and I'll be manually tuning everything for filter response anyways, but I'd rather not break the bank or solder hundreds of parts to a giant board.Maybe some kind of straightforward chip that can generate two PWM signals at variable phase from each other which I can just use on every channel?Maybe a higher speed clock divided down for a reference (used on the common of every LCD) and a count down timer to trigger the holdoff for the adjustable PWM for each channel?Is there a straightforward DAC (or cheap DAC board) who I can just throw a couple power rails at and program arbitrarily?Something else that scales well to a dozen channels or more and doesn't break the bank?Or, does someone actually have experience driving them or using this one?