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Old May 03, 2010, 09:12 PM
PLD
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That's the plan - I imagine I could end up using it for quite a few other future designs. I better make sure I accommodate for the various pin-headers that the different designs use, including some of those fancy flexible/strap leads (as per the photos you showed above)
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Old May 03, 2010, 09:31 PM
ancora imparo
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BTW, the offer on the 6.5 digit meter for calibration of the voltage refs is still there if it's any use to you.

John
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That's the plan - I imagine I could end up using it for quite a few other future designs. I better make sure I accommodate for the various pin-headers that the different designs use, including some of those fancy flexible/strap leads (as per the photos you showed above)
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Old May 03, 2010, 09:34 PM
PLD
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Ah yes, had forgotten about that - thanks.

I was planning on getting some PCBs done for the new Linear branded refs that I have, putting 1.25, 2.50 and 5.0V into the same box (all isolated of course, running off a 9V drycell).

Paul.
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Old May 04, 2010, 08:34 PM
PLD
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Hopefully the 24-bit ADCs will arrive today and we can start to get a real idea on how far this chip will go before the noise takes over. I'm planning for 20-bit resolution which is a full order of precision higher than the 16-bit.

I've also sent off an order for a PCB I drew up last night to be a graphics LCD driver, again with an AVR mega on it, though I might get away with a mega48 (4K should be more than ample I hope to hold 2 sets of bitmaps for digits, 20px and 8px high). The board won't arrive for probably 2 weeks or more.

Paul.
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Old May 04, 2010, 08:37 PM
PLD
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Oh yes, I forgot to say that after I had routed everything, I barely had 2 or 3 pins left over on the gfx driver board, so there's certainly no way I could have done both the LOM aspect and the gfx-LCD aspect on the same chip in this case, at least not without moving to a bigger AVR (mega32 or such)
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Old May 04, 2010, 11:05 PM
PLD
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24 bit ADCs arrive... still waiting on some 'odd value' resistors to arrive (different supplier).
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Old May 05, 2010, 01:10 AM
PLD
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Kelvin leads

Good news everyone, I received my Kelvin leads today... they've got shielded BNC connectors on them but I think I'll use that to my advantage for the high precision unit.
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Old May 05, 2010, 01:37 AM
ancora imparo
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Hmmm.. neat. Are they pure Cu or Cu plated tips?

John
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Good news everyone, I received my Kelvin leads today... they've got shielded BNC connectors on them but I think I'll use that to my advantage for the high precision unit.
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Old May 05, 2010, 01:42 AM
PLD
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Not sure, looks like Au plated to me. Still fortunately at least with the nature of the 4-wire setup it's not a big issue, so long as they don't corrode severely.
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Old May 05, 2010, 07:58 AM
PLD
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LOM prototype #3

Here's the high precision one showing the resistance down to 0.0001 resolution, I could in theory go to 0.000001 (that's 0.01mR) but it'll be dominated by noise and probably explode the memory requirements of the AVR (as I'll have to deal with 64-bit math)
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Old May 05, 2010, 09:10 AM
ancora imparo
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So when's production likely?
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Originally Posted by pldaniels View Post
Here's the high precision one showing the resistance down to 0.0001 resolution, I could in theory go to 0.000001 (that's 0.01mR) but it'll be dominated by noise and probably explode the memory requirements of the AVR (as I'll have to deal with 64-bit math)
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Old May 05, 2010, 10:00 AM
PLD
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Not sure when production will start... or if it will.

Just gone insane tonight as I did -something- and now the math is all wrong, I'm out by 1 bit somewhere and it's driving me bananas! Perhaps I should plug in a 16x2 LCD for the short term and fill the rest up with raw bit-dumps
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Old May 05, 2010, 10:26 AM
PLD
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Well, I got it back up and running "normally" again. I did have to use 64-bit math which ballooned the firmware size from ~4K to 7.9K. I can say already that beyond 0.1mR resolution is incredibly noisy - even the 0.1mR resolution is something you would want to take much longer term samples of.
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Old May 05, 2010, 05:45 PM
ancora imparo
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A wiser man than me once said, "The best solution is the one that gets the job done - just."

0.1mOhm from something this simple is pretty impressive. Better than that and we are starting to talk Lab gear and big money surely?

John
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Well, I got it back up and running "normally" again. I did have to use 64-bit math which ballooned the firmware size from ~4K to 7.9K. I can say already that beyond 0.1mR resolution is incredibly noisy - even the 0.1mR resolution is something you would want to take much longer term samples of.
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Old May 05, 2010, 07:26 PM
PLD
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I adjusted the firmware a bit more and made the uC go to sleep during the time that the ADC is doing its magic (about 140mS/sample), it's cut down the noise a little bit and I suspect once I mount this board into a metalised chassis and load up the front panel with BNC connectors with common grounds etc etc it should become useful.
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