Graphic LCD as a speedometer, question.

I'm thinking about using a Graphic LCD as a speedometer. But I heard those LCD displays have slow refresh, so for example display will only have 2 or 3 large digits on about full screen, and car will accelerate from 0-60 in 6 seconds, so display have to change digit 10 times a second. Is that too fast for this LCD or will it look perfect? Because when I look at this video (link below), acceleration of car is slow and it looks pretty bad, digits look like they're tearing when they change from one to another, but maybe that's because of camera. So my question is, will LCD work good for speedometer or will it bee too slow/bad? http://www.youtube.com/watch?v=0VPEyd6Y1gY

Well it would actually have to be faster than 10 times per second as the acceleration will not be quite constant. It will be capable of doing it that fast but you will have to code it right. If you try and write a number, clear the whole screen, write another number etc then you will probably have issues.
It will easily be possible to do though.

Wondering why a graphic LCD… you could use a normal character LCD with large 4 line numbers.
Take a look at multidisplay: http://code.google.com/p/multidisplay/
http://www.youtube.com/watch?v=PuyfSF7vrHQ&feature=player_embedded#!

Mowcius

Don't forget that refresh rate is also limited by our minds ability to percieve visual change. For a numeric readout, I woud think that 10 times per second is about right, but also about as fast as makes sense.

The popular 128x64 graphic LCD's would push towards max at 10 frames per second, but stiil I think they would make excellent speedometers.

How about using those huge 2.3" 7-segment LEDs? I've just built a speedo with them and response time is not an issue :)

Pic of prototype here http://www.robgray.com/grayit/diary/issue_001/lab_in_box.jpg

I originally thought about using large 7-seg led displays, but LCD kind of looks prettier. I might try both and see what’s better.

I just rode in 08 Honda Civic that has LCD speedometer, and its speedometer updates about 2 times a second at all speeds, so I guess 128x64 graphic LCD would have no problem with that.

I am thinking the same kinda thing.

10 times a second is more than enough IMHO, I remember the old Vauxhall Astra displays were slower than that and "road legal"

End of the day also, the presentation of other functions might look better too, for example an RPM bar, fuel level, etc. Suppose it just depends on what the board is capable of.

:)

I had this issue and wrote a 7-Segment display routine for the graphics LCD, basically an array of chars that hold the 7-Segment info bitwise. Some bitwise manipulation gave the segments that needed flipping, instead of refreshing the entire screen I just changed a few segments. I was using the nuelectronics.com touch shield cheap (£35 for a 2.8" touch lcd) but the refresh is insanely slow.

You don’t want the speedometer to be updated too often, that will only make it hard to read. So any LCD will be fast enough.

You don't want the speedometer to be updated too often, that will only make it hard to read. So any LCD will be fast enough.

Well hopefully they are not accelerating that fast!

Unless you had silly numbers of decimal places on your speed values, there should not be an issue reading them.

Mowcius