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desolatordan:

--- Quote from: _Sync_ on February 05, 2010, 12:17:34 am ---As I said, I think our major concern should be designing a usable ADC!

The userinterface and interfacing with other stuff is not really complicated.

I don't have much time on my hands now but I will look into reverse-engineering and drawing schematics for something that is based on the Keithley 196. This should provide a good basis from which we can work on...

And I agree, only fancy graphical interfaces would require a bigger ammount of computation time, but people get along with just 8-seg displays ;)

--- End quote ---

I agree, any of those microcontrollers would work fine. But because the analog front-end shouldn't be limited by the microcontroller, analog design can be developed parallel to microcontroller and user interface. I say whoever is most inclined to start programming with their favorite microcontroller be the deciding factor.

Get started with:
isolated external communication (ir, usb, wireless, ?)
physical user interface
graphical interface
Mastro Gippo:

--- Quote from: alm on February 04, 2010, 10:52:00 pm ---The main argument I see for using a 32-bit micro (ARM) is a graphical LCD (or OLED ;)). This might be nice for large numbers (your standard character LCD is a bit small for bench DMM IMO, and 7-segment is less flexible), dual display (like the Fluke 45) or graphs (both bar graph and histogram). I believe 8-bit micro's are a bit short on memory for this task (unless you go for the largest parts that costs more than a basic ARM).

--- End quote ---

*aehm*.. http://rossum.posterous.com/teeny-avr-media-thing-the-nanotouch-0
 ;D
GeekGirl:
If I want 32 Bit, I would go to the AVR32 line before ARM, but that is only due to the fact I have no experience with ARM :( although I am prepared to jump in an learn ;)
alm:

--- Quote from: Mastro Gippo on February 05, 2010, 07:13:43 am ---*aehm*.. http://rossum.posterous.com/teeny-avr-media-thing-the-nanotouch-0
 ;D
--- End quote ---
Yeah, as long as you can avoid using a frame buffer it can work.

It would be possible to use two different micro's for measurement and control. The HP 3478A does this: one micro connected to the ADC, and one to the buttons/display/GPIB. I don't think it would be a good idea to mix two different micro families here, since only people that know both would be able to hack it, but it's possible.

I would isolate the signals as soon as possible, as opposed to isolating USB/RS232/Ethernet. Commercial meters are often rated for about 500V between input low and ground (and more between input high and ground). The less area you have to protect, the easier (i.e. connecting buttons to this potential would mean your buttons have to be rated for 500V). It's not practical to isolate the analog signals, so I'd put the isolation device right behind the ADC (SPI is easy to isolate, there are devices for I2C), or behind the front-end micro if we go that way. Relays are isolated, not sure what the isolation rating of small-signal relays is.

The analog part is definitely the hard part, and doesn't depend on the digital part, so it seems a good idea to start there.

Alson
xani:

--- Quote from: GeekGirl on February 05, 2010, 08:22:26 am ---If I want 32 Bit, I would go to the AVR32 line before ARM, but that is only due to the fact I have no experience with ARM :( although I am prepared to jump in an learn ;)

--- End quote ---
Well both are supported by GCC so probably biggest difference would be how to configure things like SPI/UART etc., probably some code can be even ported from avr ^^
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