b***i
发帖数: 3043 | 1 可变电阻，0-10 k
ADC, 5V supply, 10 bit
如果我用10k 电阻和这个可变电阻分压，用ADC测量电压，再用公式计算就可以得到电
阻。
问题：是否需要用准确地5V供电？如果10k + vR 和 ADC都用不准确的但相等的电压，
比如4.9V
ADC读数是否还是一样？
另外，可否设计一个电流源，几百微安，那么就可以输入到vR，然后直接用5V ADC测量
电阻了。我想，ADC里不是一般有电流源吗？是不是？另外，如果用电压源和电阻，运
放，如何做电流源？ | f*****0
发帖数: 489 | 2
it can be done. you can use the 5v (Vcc) to power a resistor string
consisting of a sampling resistor and your 10K pot. the sampling
resistor needs to be much smaller than the pot.
configure the measurement so you take the voltage differential off the
sampling resistor on the high side only. By measuring the signal off the
high side, any ripple in Vcc is a common mode signal to the ADC.
however, you do need to have very precisely matched resistors for high
side measurement. this is less of an i
【在 b***i 的大作中提到】
: 可变电阻，0-10 k
: ADC, 5V supply, 10 bit
: 如果我用10k 电阻和这个可变电阻分压，用ADC测量电压，再用公式计算就可以得到电
: 阻。
: 问题：是否需要用准确地5V供电？如果10k + vR 和 ADC都用不准确的但相等的电压，
: 比如4.9V
: ADC读数是否还是一样？
: 另外，可否设计一个电流源，几百微安，那么就可以输入到vR，然后直接用5V ADC测量
: 电阻了。我想，ADC里不是一般有电流源吗？是不是？另外，如果用电压源和电阻，运
: 放，如何做电流源？
| y*****e
发帖数: 31 | 3 Build a Wheatstone bridge.
【在 b***i 的大作中提到】
: 可变电阻，0-10 k
: ADC, 5V supply, 10 bit
: 如果我用10k 电阻和这个可变电阻分压，用ADC测量电压，再用公式计算就可以得到电
: 阻。
: 问题：是否需要用准确地5V供电？如果10k + vR 和 ADC都用不准确的但相等的电压，
: 比如4.9V
: ADC读数是否还是一样？
: 另外，可否设计一个电流源，几百微安，那么就可以输入到vR，然后直接用5V ADC测量
: 电阻了。我想，ADC里不是一般有电流源吗？是不是？另外，如果用电压源和电阻，运
: 放，如何做电流源？
| f*****0
发帖数: 489 | 4 "另外，如果用电压源和电阻，运放，如何做电流源？"
an opamp's based CCS may not be useable here, due to the high minimum Vdd/
Vss an opamp needs to operate.
if you insist on doing that, you are far better of with a 3-pin voltage
reference, like lm317lz or tl431: a couple of capacitors, plut one resistor
+ your variable resistor, and you have created a voltage source whose output
changes with the variable resistor.
if you have to go down the CCS route, you may explore discrete CCS,
especially cascoded jfets: they are inc | f*****0
发帖数: 489 | 5 the solutions that are done in the analog domain (using voltage references
or CCS) are not suitable for mass production as you may need calibration for
accuracy.
another solution is to use a digital pot. the simplest would be to use a mcu
with a built-in adc (pic12f675 for example) to adjust the digital pot's
wiper so the voltage drop over the two devices are the same. the wiper's
position then represent's the trimmer's resistance.
if the digital pot uses up/down buttons (some of them do), you c |
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