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Stable voltage divider circuit

I'm using a Basic stamp to parse out a GPS string and send a beep into my motorcycle intercom in time to warn me of the info screen on said GPS showing me the details of an upcoming turn

I intend to use the microcontroler to read the temperature and also to monitor Bike voltage via and ADC.

My ADC0831 8 bit A-to-D converter reads 0 to 5v... I need to adjust my bike voltage down to fit... A resistor voltage divider seems to be the thing.. but is it going to be pretty stable (I'd like to keep a reasonable accuracy of say.... .05V I know... overkill, but I want to do it if I can...) in the temperature range of less than freezing to 40 deg C?... .is there a better way?

Al...

Reply to
Alan Adrian
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Sure there is a better way. I'm not sure if you need a reference voltage or a regulator but you can use a TL431 to get 5.00V. The TL431 is cheap yet very precise and stable, I use to read 4.99V with power supplies using it as a reference.

Tom

Reply to
T. Atkin

Reply to
saeed

There are better ways, but you don't need them. Regular metal film resistors have temperautre coeffiicients of 50ppm/C. Two combined give a worst case error of +/-100ppm/C which is 4,000ppm or 0.4% over 40C, almost exactly the resolution of your 8-bit A/D converter (one part in

256).

It you wnat to do better, you can buy +/-15ppm/C metal film precision resistors off the shelf from broad-line electronic distributors like Farnell, who also stock thin film precision dividers which offer ratio temperature coeffiicients down to about +/-5ppm/C.

For the sort of divide ratio you'd need, the dividers cost about $5 apiece - about twice what you'd pay for a pair of precision resistors.

--
Bill Sloman, Nijmegen
Reply to
bill.sloman

It depends on the bike voltage and the scaling factor of the attenuator to make it fit the full scale A/D range. The A/D range is fixed at 5V and measured with approximately 0.02V maximum error. If your input scaling is S then your scaled reading error will be S*20mV, making maximum allowable S=2.5 for maximum battery voltage range of

2.5*5=12.5V. If this is not good enough, then you will have to scale and offset so that final reading is of form S*Vm+OFFSET where S
Reply to
Fred Bloggs

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