Saturday 11 July 2015

Displaying Variety

Having seen my adventures with the new display for the little Occam's Dirk rig, Dennis, g6ybc, from Kanga sent me a sample of a Nokia display rated for 5V operation.

I tried a hook up direct to the Arduino - running the "Occam's Dirk" code - and, sure enough, the display starts up as expected...

Notice there is no 3v3 connection for power and no logic level change. There are also no resistors etc. I did run the display in the new interface board (i.e. on 3v3 supply and logic), where it also behaved perfectly.

The only difference is the function of the backlight...

On the original display, the "Light" line has to be pulled to ground to cause the backlight to illuminate. On this new unit, the same line, which is labelled "BL", has to be pulled up to light the backlight diodes.

Here you can see I've hooked up the "BL" line to 3v3 on the Arduino...

When supplied by 3v3, the backlight draws 20mA and the diodes light up normally. If you try to power the backlight from 5V, it drawas over 60mA and (to my mind) the lights are too bright. If you wanted to run the entire display off 5V, I'd recommend a series resistor on the BL line.

The photo above doesn't show the backlight too well, as the illumination is dominated by the camera flash. Here's another photo with the flash off, proving that the display backlight really is doing its stuff (at least as well as these displays ever are backlit)...

I've no idea if this device is any different than any other Nokia 5110 type display and where the claim for 5V compatible operation arises from.

All I KNOW is that it worked when I tested it (see photos above) and it survived at least for twelve hours when I left it on overnight. Beyond that, I've no more information.

These displays, which are marked with the claimed supply voltage range on the rear silkscreen...

are available from Kanga (and, do doubt, elsewhere) and would save a good deal of trouble in logic level conversion.

Fortunately, having already made my little interface board, I don't have to wonder if the claim that the display will survive 5V is correct - others can make the test for me!

...-.- de m0xpd

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