Boy did I screw up...

rjo_

I should have gotten a Hydra last year[noparse]:)[/noparse] It's amazing how stupid a reasonably smart person can be sometimes.

I'm thinking that I have a perfect application for the experimenter's card... but stop me now if I'm wrong.

I'm interested in reading a memsic 2125's temperature sensor pin (Tout)... which supposedly is a pure analog of the chip's temperature and therefore I need a good reference voltage to feed to the ADC... which is tentatively an LTC1298. How would I know whether the Hydra's power supply can provide a reference good to a level of about .01%????????

I've read the section on power supplies in Andre's book and it seems to me that as long as I don't put any other loads on it, I might get away with a one chip circuit... which would be fabulous.

I have a vague idea of what I will do with the output... but really the only thing that is crystal clear is that at 25 C the output is supposed to be 1.25 Volts and change by 5 millivolts per degree.

Ordinarily I would expect that this number would go into a polynomial expression... but apparently that isn't supplied and we have to just figure one out?

Congrats to everyone associated with the Hydra. Sorry it took me so long.


Thanks

Rich

Mike Green

The Hydra's power supply (like any other standard linear regulator) cannot provide a reference as good as you want. The regulator is pretty good, but not that good and there's some noise on the digital power supply even with a low load. There are some good temperature compensated voltage references that you could use, but that's an extra couple of parts. Some ADCs include an on-chip voltage reference.
Check the datasheets.

rjo_

Thanks Mike,

The truth is the truth... and you only speak the truth.

I have a couple of articles, but I don't remember the performance. I'll have to dig them out. This would be an important component for a lot of what I have in mind (and what I have in mind is driving down the cost of some very expensive medical equipment[noparse]:)[/noparse] If I only needed one, I'd just go buy it. I think there is a potential consumer market...(RadioShack carries accelerometers now...) and if customers actually expect to have accelerometers, the customers are going to need some good/inexpensive A to D. If we can get the RadioShack's customers to lower my costs... that would be perfect.
They are going to come to Parallax, we don't want them to go away disappointed.

Merry Christmas

Rich

Max Wooden

There was an article in the September 2007 issue of Nuts and Volts on making a .01% voltage reference. I don't have it in front of me, but I seem to recall it having a ton of great information. You may want to check it out.

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Max Wooden
Reedley, California

sam_sam_sam

Rich

If you need the Nuts and Volts article i can send to·you i get the online as well as the print
page if you need me to do·this for you Please·send·a PM with your Email Address and i will send it to you >>>>>>If this will help you

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··Thanks for any··that you may have and all of your time finding them

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Sam