I'm looking for a back-lit LCD display that has a fast rise and fall time. Right now I have a run-of-the-mill 20 by 4 LCD display showing a menu and some various other stuff. However, I want to be able to display a clock/timer. Currently, I have it showing minutes and seconds but even the seconds look sluggish. I want this clock to be able to display fractions of a second like a normal stopwatch does. This is not a write speed issue - even the normal liquid crystal library writes pretty fast, but I am using LiquidCrystalFast (because I have other operations to do via fake multi-threading). It's just the time it takes the actual LCD to update is way too slow.
Do you have any recommendations on a cost effective solution?
I always found the white on blue, white on red are sluggish. I have used several of those and switched away from them and stick with black on yellow or black on green. Go get one and try for yourself. Not sluggish. I have tons of projects with them:
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Ahh ... interesting. I have a white on blue currently. The only trouble is that this will be used at night, so I like the brightness of the current display. Are the black on green or black on yellow visible at night or do they need a "top light" to read them?
tms8c8:
Ahh ... interesting. I have a white on blue currently. The only trouble is that this will be used at night, so I like the brightness of the current display. Are the black on green or black on yellow visible at night or do they need a "top light" to read them?
Thanks!
Quite visible. You will be amazed how little light you need to read them. I sometimes use 220 ohm resistor with the back light and if I use 47 ohm, wow they are too bright.
It's just the time it takes the actual LCD to update is way too slow.
If you frequently write to the lcd, the display will appear to be grayish. If you slow down the fresh rate, they appear darker.
Also, the lcd slows down at colder temperature, as does the contrast get lower.
My favorite displays are black on yellow with back light. They are very readable under the sun, and at night, you can increase the backlight. Not so much with the white on blue types.
You need TFT display for fast switching, these have response times in the 5 to 10ms range. Passive LCDs are mainly much slower, but STN (super twisted nematic) are faster than old TN displays. Of course TFT displays get complex, but there are some bargains on eBay - some only need a few pins to drive (SPI compatible), many take 13 pins to drive (parallel 8080 interface).
Some of this could be a persistence of vision issue.
Consider that the human eye sensors charge up from the light signal and it takes time for that to fade.
(anywhere from 10-20ms)
So even if you have a very fast display, depending on how you use it, you may not be able
to actually "see" the speed of the pixels changing because of persistence of vision.
If you are seeing visible "slugishness" when seconds are being displayed (updates only once per second)
perhaps something else is going on.
Maybe you are seeing some flicker during the updates?
The key to eliminating that is to make sure you don't clear the display (EVER).
The CLEAR command is VERY slow.
You can actually home the cursor (using setcursor(0,0) NOT home() as HOME is also slow)
and repaint the full display faster than a CLEAR command.
The issue with CLEAR is that it causes the display to blank for quite some time (many milliseconds)
that is visible.
The other thing that can really help is to only update the portion of the display that has changed
vs blindly updating the full display.
I'm not sure what library you are using (LiquidCrystalFast??) and its optimization, but the standard
LiquidCrystal library is quite slow!
If you want speed, use this LiquidCrystal library replacement: https://bitbucket.org/fmalpartida/new-liquidcrystal/wiki/Home
It includes a benchmark that I wrote (LCDiSpeed in the examples) that can measure speed of
updating the lcd.
You can see the results for FM's library and the stock LiquidCrystal Library.
It would be interesting to run it on your "LiquidCrystalFast" library to see
how its speed compares to the stock LiquidCrystal library and FM's library.