Inky Impression 4 Project Questions

Support
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Hi there

I have a couple questions about a project I am working on with an Inky Impression screen and a RPi4.

I am working on a Raspberry Pi project that involves a continuous a slideshow of images on the Inky display. The images display for between 1 to 5 seconds before continuing to the next image so the majority of the time it is in the refreshing state. Every 5th image I clear the screen so that it wont damage the screen and cause ghosting or fading.

I have been writing Python code to display the images, and plan to install the Pi in a self-contained sculpture that will be wall-mounted and exhibited as part of an exhibition. I want to have zero cables coming out of the sculpture during the time that the gallery is open.

I was thinking of powering the Pi with an internal battery that can be charged without having to turn off the Pi or open up the sculpture each day. So the Pi will be always on. To achieve this, I plan to use a battery power bank with “pass-through charging” so that the Pi can stay connected and be powered by the battery while it is charging overnight.
Because I will be powering it over a power bank I am really concerned about the battery dying and then the Pi becoming corrupted. With all the GPIO pins taken I cant work out how I could set up a safe shutdown and power up switch.

I was thinking of also putting a timer on the script so that it pauses during the night when the exhibition is closed, in order to not overly stress the inky screen.

Happy to share the script I have written with the help of ChatGPT if it would be useful to see too.

My questions:
-Firstly, do you see any glaring problems with the proposal, this is my first Pi project so I am learning a lot of new things and am not sure if something I am doing is very wrong.

-Can I change the hardware script to speed up the rate of refresh, like overclocking it somehow? I ask because I had the script running from launch once and accidentally opened a new script and it did this really interesting partial refreshing where it didn’t completely load any of the images in the slide show but kind of flicked between the pulsing purple images.

-How much power does the screen actually draw? I understand it says it is ultra low power but I am trying to decide on the capacity of the power bank battery I will buy to fit internally and I am hoping that something like a 10,000 will sufficiently last each day between charges.

-Another concern is the temperature. I read that pass through charging batteries can get a lot hotter when being powered. All the electronics for this project will be incased in a seating foam so I am wondering how hot things are going to get as I don’t see any way I can get better ventilation into the sculpture.

-Has anyone got experience about putting such stress on the screen? The exhibition will last 3 weeks and be open 7 hours a day which seems like a lot of stress for it to be refreshing continuously for that time.

-What is the optimal number of images that I can show before I should clear the screen to avoid ghosting or permanent damage? Ideally I would have this happening more infrequently like every 10 images but I would rather be safe.

Thank you to any and all answers! Appreciate the feedback and help on this!

C

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If you have a less power hungry Pi I would use it, instead of a Pi 4. A 3A or Zero 2. Even a Pi Zero should be able to do what you want to do, and run on battery for a lot longer.

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I should think with a big enough battery you would be fine. It depends on how much space you have available. Does the data sheet for the Inky Impression give some idea of current draw?

I wouldn’t encase a rechargeable battery or a SMC in foam - batteries often come with a warning not to charge them in enclosed spaces, and I’d add using them to that as well. If the sculpture has a hollow part then I’d probably mount the electronics in “free space” as much as possible, so the air in the sculpture acts as a coolant. I’d put a silent fan on it as well, given that the air will not be fresh.

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A project like this, IMHO, would be beter suited to a Micro Controller like an RP2040, versus a SBC like a Pi. A Micro controller will use less power, produce less heat, and will be tolerent to total power loss.
I know, easy to say, but not so easy to do. Sometimes you just go with what you already have on hand. ;)

1 Like
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Thank you for your message.
I agree that something like a 10,000 mah should do it and any more will just brute force it in terms of having enough juice. Do you know where I can find the data sheet for the inky impression? I cannot find it on the page.

The sculpture doesn’t really have much extra space unfortunately. The sculpture where the electronics are kept is a car headrest so the its leather and foam. I was planning to cut away the foam so that the electronics slot in like a flight case. The only openings are where the poles go into the headrest so I was planning to have the battery closer or against that opening. I don’t want there to be bulges where the battery is against the leather either though.

Maybe I can get a battery that has more safety precautions about overheating. Hopefully that wont mean that they’ll just cut out when it gets to hot though…

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I did some power profiling on the Inky Frame 5.7" which is essentially a Pi Pico W with minimal extra bits to get the same screen as Impression 5.7 working to get an idea of how long they can last on three AA alkalines, detail in Instructables: Battery-Powered Digital Picture Frame Using Pimoroni Inky Frame which includes a video of the power profiling where you can see what happens during a screen refresh. There are a few open questions for that, does the current change with voltage (I think it does) and does it change with the old vs new image.

I agree with @alphanumeric’s thoughts on lowering power, a microcontroller or earlier version of Pi will reduce that which could be helpful. Some caution on manufacturers’ stated battery capacity and reduced capacity due to aging/use would be appropriate. Art galleries normally have really good temperature and humidity control but if you’re in a room which gets cold overnight that might affect your effective capacity too.

If you want to check your setup and it’s going to be below 1 amp, I’d say the Nordic Power Profiler Kit II is useful. It’s very good value for money if you have other things to use it for.

With the 30 second display update and 5 seconds pause until next update your screen is going to spend most of its time flashing. Is that want you want? I’ve had mixed responses on this along the lines of “what is it doing?”, “can it do it quicker?” and “it looks really interesting when it updates”.

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I think this whole setup is not suitable for an e-ink. E-Inks are about low-power applications, not always-on applications with a Pi4. Most E-inks will suffer if updated very often. Modern e-inks are much more robust. But it just does not make sense to show an an image for 1-5 seconds and then have an update flickering for 30 seconds.

I also agree with the other comments that the Pi4 is absolute oversized for this. If it is only a passive slideshow, the Pico will be just fine. If you do some more stuff, like image manipulations and so on, a Pi-Zero will be just fine.

Power banks are also not a good idea for running devices. They are built for other use-cases.

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A random spot that may be of interest, a teddy bear with a Pi 4 inside it powered by a power pack: Adafruit Learn: Robotic AI Bear using ChatGPT