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Topic: Cheap scope with LCD (Read 10354 times) previous topic - next topic

gnu_linux

Nice mod :)

How did you make the cut? It looks really nice and clean.

It's too bad your meter isn't working any better :(

Mine still works with the default firmware.

madworm

#61
Jul 12, 2009, 10:14 am Last Edit: Jul 12, 2009, 10:55 am by madworm Reason: 1
I used a mini mill. This investment is repaying more and more ;-)

I've downgraded to the firmware it came with (070) again. I can still make it crash by using the buttons a lot. I'm also powering it from USB now, so it isn't a bad power supply issue either. The strange thing is that when it freezes the +/- buttons don't work anymore but all the others are. I was suspecting that maybe the pins on the chip that read the buttons are bad, but looking at the schematic revealed that it is physically impossible that those two buttons are "dead" and the others still work as they share some pins. There must be something fundamentally wrong. I suspect the cpu/eeprom might be bad. I also doubt that the schematic is 100% correct. When I program the device with jumper1 removed, the cpu and the display get power but the ADC doesn't work - but it should get power too.

I wish I had never touched the firmware at all...

It seems the scope overclocks the ATmega64 to 20MHz... It's only guaranteed to work up to 16MHz. If that's not a reason for unstable operation then I don't know anything. And I call that bad design. Even if most cpus which pass factory tests at 16MHz also work at 20, some will definitely fail.

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gnu_linux

That's strange, there is a 20MHz chip with better specs than the 64-16AU which is several dollars cheaper.

The ATmega64-16AU sells for $11.83.

The ATMEGA644P-20AU sells for $7.76


In 100 unit quantities it's $6.88 vs. $4.77 so the native 20MHz part is over $2 cheaper.

So I'm not quite sure why they would continue to use the more expensive ATmega64-16AU.

The only major difference I could find is the number of I/O pins 54 vs. 32.

32pins I/O should be enough for the scope, right?

gnu_linux

What kind of mini-mill did you get by the way?

Thanks :)

madworm

http://www.emachinetool.com/new/catalog/vertical.cfm?ProductID=719

It's good enough for small PCBs and other odd jobs. There are even CNC mods for it. I haven't tested it with metal though. The nice thing about it is that it's really small and portable and not too expensive.
• Upload doesn't work? Do a loop-back test.
• There's absolutely NO excuse for not having an ISP!
• Your AVR needs a brain surgery? Use the online FUSE calculator.
My projects: RGB LED matrix, RGB LED ring, various ATtiny gadgets...
• Microsoft is not the answer. It is the question, and the answer is NO!

gnu_linux


madworm

I've been able to make it crash with the 070 firmware and a clean power supply. I've checked with my big scope that the ADC chip doesn't get any clock signal form the ATmega64 anymore when it is crashed. That could explain why the screen shows nothing anymore or at least doesn't get any updates. I've also confirmed that the CPU is only rated up to 16MHz (ATmega64-16AU) but it is clocked with 20MHz in the scope. Maybe this one doesn't tolerate 20MHz and gets upset.

To make sure it's not caused by bad solder joints, I've touched up all the pins of the ATmega and the ADC chip, but that didn't improve things at all.

I will make one last attempt to fix it by replacing the CPU hoping it works. If that doesn't help I will salvage some parts (display, switches, ADC) and the rest will go into the TRASH.
• Upload doesn't work? Do a loop-back test.
• There's absolutely NO excuse for not having an ISP!
• Your AVR needs a brain surgery? Use the online FUSE calculator.
My projects: RGB LED matrix, RGB LED ring, various ATtiny gadgets...
• Microsoft is not the answer. It is the question, and the answer is NO!

gnu_linux

Mine seems to have the ATmega64-16AU and a 20MHz crystal.

Most components can tolerate a slight overclock, but who knows.

I suppose you could try to use a native 20MHz part and see if it works better :)

madworm

Well, the 20MHz ATmega644 chips are all TQFP44 as far as I can see and I'm not going to make a new PCB for that thing.

I've checked with my scope that the "dead" buttons actually work. The signal gets to the chip, but it doesn't react. The ADC chip doesn't have a busy line or some sort of protocol, so it shouldn't be able to freeze the CPU (unless it short some pins). It could be the ADC chip, but as I also get corrupted fonts on the screen sometimes, I think it must be the CPU. Once I have a replacement ATmega, I will cut all lines to the ADC and see if it still crashes. If that's the case it simply must be a bad processor. I also could try to see if the ADC still works when the program has freezed by injecting an external clock to it and scope the data output lines for a change.

It simply has to be the damn cpu...
• Upload doesn't work? Do a loop-back test.
• There's absolutely NO excuse for not having an ISP!
• Your AVR needs a brain surgery? Use the online FUSE calculator.
My projects: RGB LED matrix, RGB LED ring, various ATtiny gadgets...
• Microsoft is not the answer. It is the question, and the answer is NO!

gnu_linux

They should have made it field replaceable.

Oh well :(

Oracle

Quote
It's good enough for small PCBs and other odd jobs. There are even CNC mods for it.


This is something I've wanted to do for a while.  I searched and the CNC mods seem to just be a few people who have done it and posted pictures with a general idea.  Do you know of any specific plans or better yet complete conversion kits?

At least for the short term, I'm looking to cut/engrave project enclosure panels.  The machine you linked might be a bit small for that. though.

Thanks

madworm

#71
Jul 13, 2009, 04:53 am Last Edit: Jul 13, 2009, 04:54 am by madworm Reason: 1
The machine indeed is SMALL, not much larger then a common food processor.

You can buy CNC enabled version of this here: http://www.usovo.de/shop/index.php?cat=c9_CNC-Milling-Machines.html

They also have bigger ones for more serious task and ones with longer x-travel. Of course they cost more than just 300?. Last time I checked, you could also get an upgrade KIT for it. Unless you want this particular machine, I'm sure you can find similar ones on your continent. As with every piece of machinery, good stuff ain't cheap.
• Upload doesn't work? Do a loop-back test.
• There's absolutely NO excuse for not having an ISP!
• Your AVR needs a brain surgery? Use the online FUSE calculator.
My projects: RGB LED matrix, RGB LED ring, various ATtiny gadgets...
• Microsoft is not the answer. It is the question, and the answer is NO!

RoyK

I got mine Saturday and am having fun with it. The display is a bit dim for my old eyes but otherwise it works fine.

I've been trying to find a schematic for the beast but haven't had any luck. Can someone point me to one?

madworm

The DIY KIT contains a schematic. It's a bit low quality as small colored text was rastered on the BW laser printout. I could scan it when I get back home. Its pretty simple and straight forward. The only "nifty" stuff is the negative voltage creation for the opamps (at least from my point of view).
• Upload doesn't work? Do a loop-back test.
• There's absolutely NO excuse for not having an ISP!
• Your AVR needs a brain surgery? Use the online FUSE calculator.
My projects: RGB LED matrix, RGB LED ring, various ATtiny gadgets...
• Microsoft is not the answer. It is the question, and the answer is NO!

RoyK

Quote
The DIY KIT contains a schematic. It's a bit low quality as small colored text was rastered on the BW laser printout. I could scan it when I get back home. Its pretty simple and straight forward. The only "nifty" stuff is the negative voltage creation for the opamps (at least from my point of view).


That would be great! Thank you.

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