| Electronics > Projects, Designs, and Technical Stuff |
| Building another DIY DMM based on MSP430i2xx |
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| Miyuki:
Hi folks, I want just for fun and because it can be done build own DMM with reasonable resolution and features And also to learn how to use MSP430 platform (as even it is old still very popular line) They have nice metering family MSP430i2xx with up to 4 24bit SDAC, they are cheap with reasonable precision, whole chip cost like alone 24 bit ADC or just similar spec voltage reference Also it is nice to have multiple ADC to measure voltage and current together to have power calculation with all details like PF and so (as they have reference design for power meters), and measure low frequency RMS and average values by direct sampling |
| Yansi:
24bit SDADC with what ENOB? Either way, you need a multimeter frontend, which is your major issue designing a multimeter. Picking a suitable ADC is the least concern for a generic DMM. (Most multimeter chipsets already have the ADC integrated anyway...) |
| Miyuki:
It have 14.5 with internal reference and 13.5 at 8x input gain, it is plenty of resolution And it can use fewer steps at range divider (like 100x) No need to use rectification at fronted, just measure AD directly Basically "just" divider with protections (I know this can be tricky) |
| Yansi:
And how about the range switching? Input protection? Ohms mode? Amps measurement? It is not that easy. I have tried to make a custom DMM platform for logging purposes. Not that easy. Ditched it completely. There were all sorts of issues. 13bit ENOB for 24b SDADC is piss poor performance. Thought you've picked 24b ADC due to requiring performance. :) |
| Miyuki:
It is resolution at 4ksps (specified for Fin = 50Hz) for DC it can be further increased Switch something like 3157 switch, with auto range Input protection at Voltage classic PTC and MOV, with diodes after divider Amp measurement classic fuses with diodes over shunt Ohm/continuity mode work like at AVR transistor tester, just will have this protection Voltage input uses But even failure will be good as experience |
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