i2c controlled power supply : Flicker free ILI9341 - The problem


I bought a few ILI9341 LCD screens on ebay. I intend to use them for the i2c controlled power supply.
Why those ?

  • They are cheap, big enough
  • Using the block update, they are fast. Basically define a rectangle on the screen and send all the data in one transaction. This is much faster than drawing  pixel per pixel or even line by line


We have a nice driver for STM32 -arduino using that blockmode.
That driver is indeed very fast.

With one issue : font management


Going back in time, that driver is derived from the Adafruit one
With the Adafruit one, you can use pseudo ttf font, with variable width/height. 
Pick any font you like, use fontconvert to generate the fontxxxxx .h and done.
Since they are variable width, the result looks natural.

The problem is when overwriting.
Since it is variable width/height you cannot just overwrite the old text with the new one, some leftovers may stick.
For example, replacing "ZZZZ" by "llll" will create "llllZ" because the "l" are much narrower.

NB: It is actually more complicated, because that driver only draws what's needed, so you'll also got leftovers above/below/right/left when printing small things on top of larger ones.

So the usual way is to first blank the maximum area, then print over it


Problem solved ?
Not really, that creates major flickering. In the example above you'll erase the "ZZZZ" first, THEN draw the "llll". Even if the driver is fast, it will definitively flicker.



The STM32 driver takes a different approach : It uses fixed width font.
So no problem, just overwrite the old text with the new one, they'll take the same space, no leftover anywhere.
BUT
  • It does not look very natural. An "i" is taking the same space as a "Z", same for "." or ",".
  • You cannot pick any font you want, in any size

So let's make something in between combining the best of both.

Comments

Post a Comment

Popular posts from this blog

Component tester with STM32 : Part 1 ADC, Resistor

Image
I was always  fascinated by the so call "transistor testers" that identify and report pin out, features of pretty much whatever you throw at it. They are based on Atmel 328p chip, the same as arduino nano. So why not do the same thing with a STM32/Bluepill ? The STM32 is faster, has a better ADC accuracy, more memory, can do float etc... and is not more expensive. Warning : I'm doing this for fun & to learn, it might contain error & plain misunderstanding So, i watched a couple of video on the general principle on how they work. This is not a "port" but a rewrite from ~ scratch. When something is weird, i check what the original one does for comparison. Measuring resistance So first thing first :  Resistance & Capacitance. These 2 will unlock the other ones. So how do we measure resistance ? What we do is a resistor divider with a know resistance value: Measure = Vcc*(RtoTest/(RtoTest+Rknown)) As far as the ADC goes, it means ADC=
Read more

Fixing the INA3221

Image
It 's not too complicated to change the board we have seen  previously . You 'll need to cut some tracks, i did it with a dremel and i'm not very handy, so you'll do better. Red =Cut tracks Blue = Add wire 1- You'll need to separate the bottom connector from the ground, cut the 3 connectors BOTH SIDES. 2- Remove the small red area below the middle resistor to isolate each channels from each other Last, connect right side of each connector to the now isolated pad. Mine looks like this after the operation (ugly i know): Be wary of the small track on the left connector that leads to the left side of channel3 resistor. I cut it while isolating the right pad. Now it works, we can go back to the charger.
Read more

INA3221, weird wiring

Image
Continuing my "smart" battery charger, i've finally received the INA3221 module. It is the purple one you can find on ebay for ~ 5 bucks I soldered a couple of pins to be able to connect it so that i could test it and something immediately caught my attention. It is supposed to be a high side current/voltage sensor, typically in a setup like that : So you can measure the voltage supplied to the load, and the current going through it. Now, let's have a look at the module, look at the top of the following pic, where the sense connectors are. CH3/GND/CH2/GND/CH1/GND ? Wait ? What ? Yes, all the IN- pins are connected to ground, so it is a bottom current only sensor. Additionally, the - side of the shunts are ALSO connected to the ground, no only the connectors. The actual layout is like that : That raises two problems :  The voltage is meaningless as we are only measuring Current x ShuntValue, not the supply volt
Read more