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Topic: [solved] Sainsmart LCD Keypad Shield hardware bug! (Read 442 times) previous topic - next topic

RIN67630

Jul 30, 2019, 08:42 pm Last Edit: Jul 31, 2019, 08:11 am by RIN67630
The design of the Sainsmart LCD Keypad Shield is really stupid!

The keys are transformed into an analog signal through a resistor network.
OK so far.

But the hot line of the resistor network is hard-connected to Vcc instead of Aref.

So if you want to use analogReference=(INTERNAL) or analogReference=(EXTERNAL), the keys won't work!

I am looking forward to modify the shield, but it does not seem to be easily doable since the resistors are located behind the display.

 :smiley-mad:

I just do not want to modify the analogReference=(DEFAULT) on the fly, that is IMHO too dirty programming to circumvent a hardware bug.

RIN67630

#1
Jul 30, 2019, 09:38 pm Last Edit: Jul 31, 2019, 08:11 am by RIN67630
Finally it could have been worse.

It took me 10 minutes with a minidrill to cut the wire and solder another one to Aref.

You need to lift a bit the display and cut the track right of R2:

Then you solder a wire close to R2:

And finally solder the wire on the other side to Aref:


Done!
Now my keys are recognised for every analogReference=(whatever).

Enjoy

Paul__B


RIN67630

#3
Jul 31, 2019, 04:32 am Last Edit: Jul 31, 2019, 08:10 am by RIN67630
And you read this thread, didn't you?
That's a completely different issue addressing the control of the backlight through D10.

I am speaking about the keys reading circuit that won't work if you need analogReference=(INTERNAL) or analogReference=(EXTERNAL).


Paul__B

That's a completely different issue addressing the control of the backlight through D10.
But it is meaningful.

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