Memory LCD Displays

[SiliconWizard]

Many of you probably already know the Sharp memory LCDs, which they first released over 10 years ago. The first one (that I know of at least) was a 96x96 display with a very reflective layer - black pixels were actually appearing almost as a mirror. That looked cool but wasn't all that great with too much ambient light.

The following ones were all with a more conventional "black". I've used the 400x240 monochrome, 2.7" in one project, fantastic display drawing only a few µA on average. This is the one that SwissMicros also use for their DM42 calculator. Reference is LS027B7DH01.

You can find their current offering there: https://www.sharpsecd.com/#/memory-in-pixel-lcds-product

The color ones are also interesting. I had tested their first (I think) color one a few years ago, a 1.3", 8-color one (that is now obsolete apparently), but their newer ones are 64-color. Not tested yet.

The downside is... they are relatively expensive.

I've seen alternative ones appear from other vendors, much more affordable. One of them is JDI. An example: https://www.panelook.com/LPM013M126A_JDI_1.28_LCM_overview_26471.html
seems like datasheets for JDI displays are hard to find, if anyone can find a reliable source.

Also found one that is 250x122 monochrome, pretty cheap compared to the Sharp ones: https://www.alibaba.com/product-detail/2-13-122x250-Monochrome-Reflective-TFT_62423861108.html
I ordered a few of these to test (can be found on Aliexpress too).

Have you used this kind of displays before, and do you know of any that I wouldn't have mentioned here?

[I wanted a rude username]

Used the older Sharp ones a while back but agree they're a bit underwhelming. The ultra low power ones (< 5 µA static image) all have poor reflectance (< 10%), looking greyish.

I suspect (but don't have any evidence) that MIP-equipped Garmin watches use the JDI ones, because they have much higher claimed reflectance (26%) and the Garmin watches' displays actually look close to white. But would love to know for sure.

Haven't been able to track down a datasheet for the JDI displays either, so I don't know if they require an external ~2 Hz clock input for toggling the LCD drive polarity the way the Sharp Memory Displays do (if I recall correctly ... at least in order to run at the lowest power).

[SiliconWizard]

The 2.7" Sharp one has relatively good performance. Blacks look pretty black to me.
The color one I had was nice, but with very washed out colors. Not unusual for this kind of display though.
As I said, haven't tested the newer Sharp displays, so maybe they are significantly better, especially the color ones.

The 250x122 I mentioned (which is apparently from a chinese vendor) uses a ST7302 controller (datasheet can be found) and it doesn't require external toggling for refresh, as do the Sharp displays. It's built-in. It has two refresh rates actually, programmable, one for a higher power mode and one for a low power mode. They are very cheap in comparison. The controller being a Sitronix one has way more features as well than the Sharp displays which have pretty basic, custom controllers.

[I wanted a rude username]

The Sitronix ST7302 datasheet and that Alibaba listing for the B213HWG01 display both avoid giving power consumption figures ... surprising because the major selling point of MIP displays is low power. I guess those displays are not in the microamp realm ... hopefully your application can tolerate that.

By "greyish" I meant the colour of the pixels in their lighter, transparent state. On the MIP displays that Garmin uses, this is a much lighter grey than on the Sharp or Dongguan Shineworld ones. The contrast ratio is ballpark similar, but the effect is that these lighter displays are way more legible, especially in low light. IRL they can be impressive ... for nerds like us anyway. 

Curious to see if those displays from Alibaba suit you and your application's energy budget.

[SiliconWizard]

I see for the grey. Yes, the background, basically. It's still not bad IMO, but it's far from the white that you can get with eInk indeed. Actually, with the 2.7" display, my UI was in reverse - I used the black as background, and it looked better. But that may not fit all UIs.

As to the B213HWG01, there are tests out there showing it draws around 20-25µA on average in low-power mode. That's higher than the Sharp displays, but still pretty good. I'll measure that when I receive them to confirm.

But the reason you need to toggle a pin (or alternatively send an instruction) of the Sharp's controllers is that they probably don't run any internal clock when they are in "standby", while the ST7302 does since it can handle refresh on its own.

In the DS I got for the ST7302, the DC characteristics are given. They say 160µA typ. for the controller for VDD=3.0V. But they don't say in which operating condition it is exactly. Tests you can see elsewhere show 25µA. So I'll see.

I got the 8-color Sharp display out of a drawer and I'm curious to test it again. If I get around to it, I'll post a pic. One "downside" with those displays is that they need a 5V supply. At only a few µA, you can easily generate that with a GPIO and a couple diodes and caps, but that's still something to handle and that will slightly add to the overall consumption.

[SiliconWizard]

I got the ST7302-based displays, but haven't tested them yet. That should be soon.

Meanwhile, I've made a quick test of this color ( 8 ) memory LCD I was talking about. The photo doesn't give it full justice, but that'll give you an idea.
Since there's less contrast with colors than with the black, you need good lighting to clearly see them. Probably of limited use these days (and there are newer ones with 64 colors and better contrast), but that was kind of cool when it got released.
It draws less than 5 µA to retain the display, and the refresh pulse needed can be generated with an extremely low period (several seconds) before you start noticing the slightest decay. So in terms of power consumption these are pretty amazing.

Also, the display is amazingly thin (< 0.5 mm).

[SiliconWizard]

Here's the test with the B213HWG01. The contrast is pretty good. It's on par with the Sharp displays.

It has two power modes (high/low). One can set the refresh rate for each mode. The highest is 32 Hz and lowest 0.25 Hz. I set it to 32 Hz / 0.25 Hz, display some stuff and then put it in low-power mode (along with the MCU) and measure the current. I see absolutely no difference in the image between the high- and low-power modes.

In low-power mode (image maintained), the display draws an average of 11.5 µA. Looking at the current profile, I see some short current spikes every few hundreds of ms of about 160 µA, but on average, it's about 11.5 µA. The current between those short spikes is about 9.5 µA.

So, it's better than I expected. Given its price tag, it's a win in my book.

Beware of the silightly nasty ST7302 though, which orders pixels in its internal memory in a rather funky way, requiring some not-so-fun encoding before sending data to the display. Otherwise, it's all fine.

[SiliconWizard]

Note that the ST7302 is apparently EOL, making those displays probably just "stock while it lasts". Too bad.
https://www.palmtech.com.tw/news/news/sitronix-products-end-of-life-notification

EDIT:
There appears to be newer variants of those LCD panels with a ST7306 controller (which is newer and active in Sitronix catalog). The datasheet is also easier to find.
You can find these here, for instance: https://displaysino.com/product_details/2.13-inch-smart-switch-TFT-Display-122x250-ST7306-LCD-TFT-Reflective-Display.html

Otherwise, I've done some more extensive testing, so here are a few additional notes:

- The hardware reset time looks oddly "temperamental". The datasheet is not crystal clear about it, it gives two delays basically (1 ms max, or 120 ms if the display was in sleep mode when you hardware-reset it, if I understand correctly, go figure). Either way, when you just hw-reset it but don't power cycle it, the startup time after reset looks unpredictable, and sometimes just 1 ms will work, but other times, it requires up to at least 200 ms before sending any command, otherwise it doesn't operate properly. So my guess is that it may all depend on what state the controller was in exactly when resetting it, but it's like a black box. And, they recommend always hw-resetting it after power-on to make sure it's properly initialized, so that basically means that if you want something reliable, there is this 200 ms delay. Not a huge deal, but something to know.

- The various controller parameters (like gate driver settings, voltages, etc) needed for this panel are undocumented. One can find init sequences that "work" in a few drivers one can find online, but these parameters actually only work in low-power mode (which has limited frame rates, up to 8 Hz).  For the high-power mode (16 & 32 Hz), these parameters are not adapted at all and the display flickers like crazy - completely unusable. Whether one can find parameters that will work for the higher refresh rates, I'm going to try and see. I've already tried some change to no avail. It may be possible that this panel can't even support these higher frame rates at all.

Some links of drivers if you want to get init. sequences that will at least get you started:
https://github.com/zhcong/ST7302-for-arduino
https://github.com/elulis/micropython_ST7302

[uer166]

Looking for a 240x400 Sharp memory equivalent for my project (the display is amazing, but the price is not right). Hopefully something relevant exists. Also trying to figure out a front-lighting scheme which is not easy.

[SiliconWizard]

There is this with a ST7306 controller and higher resolution (400x300): https://www.good-display.com/product/455.html
They seem to have the same panel with a ST7301 controller: https://ifan-display.com/product/4-2-inch-monochrome-lcd-300x400/
Significantly larger though.

If you're looking for a drop-in replacement, JDI has the same panel: LPM027M128B/C
https://www.panelook.com/LPM027M128C_JDI_2.7_LCM_parameter_28568.html
Although I suspect you can find it for cheaper than the Sharp one, I'm not sure about that.

[uer166]

There is this with a ST7306 controller and higher resolution (400x300): https://www.good-display.com/product/455.html
They seem to have the same panel with a ST7301 controller: https://ifan-display.com/product/4-2-inch-monochrome-lcd-300x400/
Significantly larger though.

If you're looking for a drop-in replacement, JDI has the same panel: LPM027M128B/C
https://www.panelook.com/LPM027M128C_JDI_2.7_LCM_parameter_28568.html
Although I suspect you can find it for cheaper than the Sharp one, I'm not sure about that.

Not looking for a drop-in, but these options are a bit iffy though interesting: first is too big for the handheld device, second is pretty neat, but unavailable and being RGB has a bit different requirements. It does open a whole new world of GUI possibilities, with added complexity.

[SiliconWizard]

Note that the ST7301/02/06 all have this funky pixel memory organization that requires painful encoding for sending data to the display. So, if you have very limited performance on your board (especially for larger resolutions) and can't afford a full framebuffer in RAM, then it's something to definitely consider.

Is power consumption a significant factor in your case? If not (at least if you aren't looking to shave off the last µA), you could consider more conventional graphic reflective LCD than those memory-in-pixel panels, which are way more expensive.

[uer166]

I'm not looking to save the last possible uA, my total system power consumption is dominated by LoRa and GNSS, something like 15mA average.

I've looked at a lot of conventional options, but never found anything that is as pixel-dense as a memory display. I certainly don't need it to be memory, but found nothing else that's in the 2.7 inch size and high PPI density (monochrome or perhaps greyscale specifically).

[SiliconWizard]

Yes, it's become tough to find high-res monochrome panels.
Sharp have newer ones (as posted in an earlier post) with colors and higher res. But, price is a problem.

Color TFT panels are everywhere and so have become very cheap. Unfortunately, if you want high-res and cheap, that's pretty much the only option. You get backlight and colors as a bonus. But the power consumption becomes a problem.

This is a nice one (it's one of the newer Sharp MIP color displays, but with an added layer for great front lighting): https://www.azumotech.com/products/3-4-14793-01-64-color-display-mip/
it's a bit, uh, expensive though.