As mentioned in an earlier post
I'll try to do one small PCB project every week and then send for PCB's of it every Monday.
This week I'm in Bangkok for some business meetings, but it won't stop me from doing this weeks PAW.
Since the last PAW was about as simple as it can be, just a small pcb with a bunch of holes drilled into it, I'll plan to do something a little bit more fancy for the PAW.
Unless you have a properly calibrated "serious" DMM like the Agilent 34410A
or the 8.5 digit Agilent 3458A
or even a Fluke 87V you really can't be sure that your $20-$50 DMM is displaying values that are not too far from the real value.
So a high precision voltage (and possibly also a semi-high precision current) generator might come in handy to check the accuracy of your DMMs.
-series are high precision voltage references (max 0.02% error) and a typical tempco 0.5ppm/°C (=0.00005%) so it basically won't be affected by temperature variations at all.
The 0.02% error might sound very good, but it's actually 1 mV for a 5 volt reference, so the output could theoretically be 5.001 volts. This is good enough to calibrate a standard 3.5 digit DMM, but it might be nice to have something more. Luckliy the output can be adjusted for higher precision if needed, something that of course woule require a properly calibrated 6.5 or 8.5 digit meter to do...
If I would to sell a few of these boards (pre-built) I'm thinking of having my 6.5 digit Agilent re-calibrated and certified so those MrRefs could be calibrated for an order of magnitude higher precision than the initial 1 mV.
The MAX6350 is available in 2.500, 4.096 and 5.000 volt versions and I'm leaning towards the 5 volt version and then possibly either include a selected high precision resistor to add a 1mA output on the board as well or including a voltage divider to add a 1 volt output.
The chip needs at least 8 volts to do its job properly so I plan to run it from four lithium button cells in series.I think that the 1mA current output would come in more handy than a 1 volt output - what do you think?
The output terminals would of course be gold plated 4mm banana jacks, but I'm debating with myself if I have to put them at the "standard" 3/4 inch distance or not. It would be much easier to make a small pcb without this constraint. Any thoughts?