I am planning to build a count-down timer for yacht racing starts. I have settled on a pi pico W with a Waveshare 2.9inch E-Paper Module for Raspberry Pi Pico 296x128 (Black/White) as the display. I’ve found other types of screen are unreadale in bright sunlight on a pitching deck and 7 segment displays are too clunky.
The E-Paper screen seemed to meet my need with a 0.3s partial refresh time (for the seconds digits) and 2s for a full screen refresh when needed.
My problem is the Waveshare website has some dire, but pretty vague, warnings about refresh:
For E-paper displays that support partial refresh, please note that you cannot refresh them with the partial refresh mode all the time. After refreshing partially several times, you need to fully refresh EPD once. Otherwise, the display effect will be abnormal, which cannot be repaired! ---- I wonder how many “several” is.
it is recommended that the refresh interval be at least 180s – If I understand this right, this pretty well rules out use as a race start timer. I see you have examples on your site of the screen being used a s a clock - how is that possible if you can only refresh every 180s?
Unfortunately not a lot of manufacturers publish this number. It might be due to variability in operating conditions or how the displays are made. This Maker runs the partial refresh >10 times without any ghosting (presumably on a new display). As long as a full refresh occurs after the rapid countdowns you should be all good!
This is the minimum suggested full refresh interval, i.e. you’ll want to make sure the display is updated at least this often, smaller intervals are fine!
While these may be suggested limitations you likely wont break the modules straight away - feel free to experiment with them!
Hi Charles
You are right. I thoroughly agree. If I were you I would clarify this. It should be one way or the other. Waveshare statement and Liam’s interpretation are directly opposed. Although being Waveshare I suppose anything is possible.
Cheers Bob
I may not have explained this too well, to make sure ghosting due to a persistent colour on the screen you’ll want to update the e-paper at some intervals (<180s, or atleast 180 seconds).
