2.8" TFT Touch Shield works only with some Mega 2560 R3s?

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pburgess
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by pburgess »

One, er, two other questions...when running the shield on the older R3 boards (where it works), what LCD driver ID is reported in the serial monitor? Presumably you're powering these via USB...in which case, are these connected to a powered hub? Have you tried connecting a DC power supply to see if there's any change?

Not aware of any schematic or component changes in the Mega boards. There's the thing with the power supply caps, but in principle that shouldn't be changing anything.

prabbit
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by prabbit »

The old silkscreen boards (working) send back over Serial:
Paint!
Found ILI9325 LDC driver

This comes back both when externally powered and when only powered over USB (connected directly to my laptop).

If I repeat the test with the new-silkscreen (not working) boards) I get:
PaPaPaPaPaPaPaPaPaPa

with another "Pa" added on about every 0.5 seconds or so. This behavior is also the same whether the board is externally powered or not. It seems the external power does not affect the behavior of either the working (old silkscreen) or non-working (new silkscreen) Mega R3s.

Incidentally, I found a Mega ADK laying around and gave it a try and the LCD works just fine.

prabbit
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by prabbit »

Pburgess, presumably you've got one new silkscreen R3s and a Touch Shield. Have you been able to duplicate the issue?

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pburgess
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by pburgess »

I don't have one of the new R3s. I think someone at HQ was going to give it a shot...if not, I'll get ahold of the parts and try the same combo.

It seemed like it could be a brownout issue, but apparently not.

prabbit
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by prabbit »

I'm trying to come up with a work-around (or a source for the old-silkscreen Mega R3s) to ease the urgency as this seems to be more difficult to figure out than I was hoping. I will be on travel next week and will not have access to the forums, but I'll check back when I return and hopefully we'll be able to figure this one out.

It would be very good to have someone else verify the behavior of the new-silkscreen R3s with the Touch Shield because it's 100% consistent here, but also seems so bizarre because the old-silkscreen R3s worked so reliably with the Touch Shield. Thanks.

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pburgess
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by pburgess »

I don't have a fix yet, but wanted to mention that I've been able to replicate the problem here with the latest "white silkscreen" Arduino Mega and two different versions of the shield. It's not just you. Looking into it...

prabbit
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by prabbit »

pburgess, thanks for verifying that I haven't lost my mind (at least on this issue). It looks like my two "old-silkscreen" Megas just became incredibly valuable (despite a few blown inputs from a previously misbehaving circuit).

I definitely look forward to hearing what you come up with. In the mean time, do you have a source for the old-silkscreen Megas?

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pburgess
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by pburgess »

Not a "sure thing" source, no, but my local Radio Shack had the Mega ADK R3 on clearance, and I've confirmed this works with the shield.

prabbit
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by prabbit »

That's a good idea. I'll cruise to Radioshack and see if I can't find any of the old layout.

Have you had any luck figuring out what's going on? I'm feeling pretty exposed right now not having a fix if any of the existing Mega R3 boards go bad.

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pburgess
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by pburgess »

Not yet, but it does appear to be hardware related. It's been brought to the Arduino folks' attention, hopefully some sort of fix will be possible.

prabbit
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by prabbit »

Yikes. That's not good. Is there a list of the changes somewhere? This is open source, after all.

If it's the same layout, that seems unlikely. Component changes, however, seem to be a much more likely possibility. I haven't looked into it at all, but my guess is that the Mega is resetting through the reset pin, which could be cause by a component change secondary parameter (cap with higher series resistance, resistor with higher capacitance, ...) coupling back through to cause a reset. Just a guess.

Please keep me posted. I definitely wasn't expecting anything like this when I ordered a few more boards to build out my already working system. Yikes. Thanks for pursuing it.

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pburgess
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by pburgess »

Okay, we've had some back-and-forth with the folks at Arduino HQ, and there's good news and bad news...

Bad: the current iteration of the Arduino Mega 2560 board (identified by the 2/3 solid white silkscreen on the back) is not compatible with the 2.8" TFT touch shield...and we also discovered that NeoPixels can't be driven from pins A0-A15.

Good: there's a fairly simple fix.

Bad: it requires soldering a tiny part.

Good: if that's not an option, we can at least offer a refund on your two boards. Some future batch of Megas will likely incorporate this fix, but we have no idea when this would happen nor how quickly this would filter through the pipeline as existing inventories are restocked, so we can't just issue replacements right now because they'd be from the same batch.

If you'd like to perform the fix yourself:

You will need a 0.1 microfarad capacitor. Preferably surface mount, but it could also be done by bending the legs of a small through-hole capacitor.

Look for this unpopulated spot on the board, it's right next to another component:
add-cap.jpg
add-cap.jpg (28.08 KiB) Viewed 320 times
Solder 0.1 μF cap across those pads. TFT touch shield should then work.

If you'd prefer a refund: email [email protected], include a link to this post and your order number, and we'll get that squared away. Thanks for your patience with this...it required a lot of detective work!

prabbit
 
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Re: 2.8" TFT Touch Shield works only with some Mega 2560 R3s?

Post by prabbit »

Thanks for getting to the bottom of that. I'm going to get the caps and try the fix myself.

Can you give a bit more background on what happened? Was the cap removed from the previous layout? If so, why? What else might be affected?

Thanks again.

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