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Community Bench Meter
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xani:
Maybe use some small ARM instead ? More horsepower and interfaces, like for example  AT91SAM7X256 , builtin Ethernet and USB, ok price and plenty of space in flash and RAM.
Then we could add things like USB<=>SPI/I2C/USART debugger or serial bus monitor on LCD. Or telnet into your meter from work ;)
Curtisbeef:
I like the MicroSD card idea. Its simple enough to put a 8GB storage card in there for many hours of data logging and they are super simple to interface with almost 0 extra parts(besides the connector). Id definitely say go with the MicroSD over the standard SD the size makes it way better and there are no downsides.

USB PC Connection is a MUST.
I love Dave's idea about about having a simple serial terminal. That would be a Awesome feature. If we are gonna go that route might as well add I2C and SPI Analyzers Etc...

My opinion about the Ethernet is that it kinda adds a huge amount of complexity / expensive parts for a feature that I don't know how useful it would be to most people. But like was said before we could always go for a modular type of a system where that could be a addon feature or something.

For Micro I would probably suggest some type of MSP430 because they are know for using like insane low amounts of power. And there are a TON of options. But if we are going for Horsepower ARM would definitely be a good option.

I love the idea of making it handheldish..../portable but if you guys wanna make it a bench tool thats cool too.
xani:
SD have one advantage over MicroSD, you can use card from your old phone/camera in your meter ;]. Or just make connection on PCB to both SD and MicroSD socket, problem solved ;]

About ethernet, i think that using something like "Ethernet shield" for  8 bit uC is a overkill (more expensive than main CPU) but if we use some stronger CPU we could just use one with buildin Ethernet/USB (like that AT91SAM7X256 which is about $10 here in Poland). And Power over Ethernet/USB option would be nice also, one less cable on bench ;]

About power consumption,  we could add option to power off some parts of meter, like USB and Ethernet when on battery power and/or downclock CPU when on battery and not doing anything computation heavy work.
Mastro Gippo:
Usb and ethernet cables on a multimeter are just a disaster waiting to happen. It's not a good idea to connect a multimeter to the common ground, because if you don't isolate everything you will end up shorting things to ground if you measure a signal with a floating reference. I think wireless (bluetooth, zigbee, custom 2.4ghz) is a better option.

I don't see any benefit in using an ARM, I think all the tasks we need can be easily handled by an easier micro.

I suggested the microSD because they're, well, micro, but a regular slot will be ok too because you can find adapters everywhere.

Sorry Dave, but I think that a rechargeable battery is a must if we want an OLED diaplay, wireless, SD slot.... But I wouldn't go the SLA route, li-ion are cheap and easy to work with, SLA weigh a lot and has Peukert and is big...

We should try to focus on building a meter, and keeping it simple and useful (and CHEAP!!); I understand the enthusiasm, but adding tons of features that don't belong to a meter will only be frustrating in the end imho.  :)
jahonen:

--- Quote from: Curtisbeef on January 27, 2010, 12:50:16 pm ---USB PC Connection is a MUST.
I love Dave's idea about about having a simple serial terminal. That would be a Awesome feature. If we are gonna go that route might as well add I2C and SPI Analyzers Etc...

My opinion about the Ethernet is that it kinda adds a huge amount of complexity / expensive parts for a feature that I don't know how useful it would be to most people. But like was said before we could always go for a modular type of a system where that could be a addon feature or something.

--- End quote ---

The advantages of ethernet over USB are:

1. No need for writing device drivers at computer end. All necessary things are already in every operating system on the world. Yes, you can use those RS-232-USB converters, but they still require a driver.
2. Easy galvanic isolation (in fact ethernet standard requires transformers at both ends).
3. Is not operating system dependent.
4. Long distances (>5m) easily achieved, communicates easily to other side of the globe if required :)

That serial terminal is also easily implemented over TCP/IP using telnet. Ethernet is replacing the venerable GPIB slowly, most modern serious measurement equipment is equipped with LXI (LAN eXtensions for Instrumentation). Some kind of compatibility with HP34401 etc command set would be also nice. So you can actually say "MEAS:VOLT:DC?" to the meter (using that telnet) and it will perform a DC voltage measurement and return the result using plain ASCII. That makes it easy to program your automated testing system :)

Of course, that becomes with the price tag of more complex embedded software, but 32-bit ARMs (7TDMI, Cortex-M3) etc. are very cheap nowadays. Actually so cheap that one should think very carefully before using 8-bit ones, from the price standpoint.

Regards,
Janne
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