Can you measure millivolts?

dhj2003

I was looking at the documentation but can't seem to find·what i'm looking for.·Can any of the basic stamps be setup to measure millivolts from 0 - 10 volts. Any help would be appreciated. Thanks. Jordan

Lee Harker

If you wish to measure analog voltages with the Basic Stamp you will need to use an A to D converter. One of the important decisions to make in your case is the resolution needed. Consider a 12 bit ADC, you could measure 0-10 volts in ~2.4mV steps. If you need greater resolution than that, the price starts to creep up. There are lots of choices for ADCs. Unless high speed is necessary, a serial ADC would be a good choice by freeing up quite a few I/O pins.
Hope this helps.

dhj2003

Thanks Lee. I found a TI ADC with 4 analog inputs with serial communications. Just what I was needing. Thanks again! Jordan

sam_sam_sam

dhj2003



Thanks Lee. I found a TI ADC with 4 analog inputs with serial communications. Just what I was needing. Thanks again! Jordan

Can you share where and what type· ADC· you are going to use
Can you also share where you are buyimg them at with a web page link

Thank You for your help and time in this matter




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Sam

dhj2003

Texas Instruments makes the ones i'm looking at Sam. I am still researching but here is a little info on the MSP430F11x1 Sigma-Delta Type Millivolt Meter. I will have to find somewhere to puchase also so I don't know where i'm getting them yet. Hope this helped.

Jordan

The concept of an integrating A/D converter is to match an unknown voltage of interest Vin, with
a known voltage, Vout. Using a single digital output, the MSP430F11x1 implements a 1-bit
digital to analog converter (DAC). The DAC outputs a controlled number of short symmetrical
pulses to generate an output density to drive Vout equal to Vin. Software modulates and counts
the DAC output pulses of a fixed length loop. The DAC is low-pass filtered, creating a constant
analog voltage Vout. See Figure 2. The software feedback loop compares the analog voltage
Vout to the interesting voltage Vin using comparator_A, modulating the DAC output pulse such
that two analog voltages are maintained equal. Over a fixed number of symmetric DAC pulses,
the feedback loop integrates the number of high DAC outputs (n) required to maintain Vout
equal to Vin. The feedback loop can be modified in length to deliver the required resolution. For
example, a loop of 256 counts would correspond to an 8-bit conversion, 4096 counts to a 12-bit
conversion. In the demonstration circuit, the count of 3300 is selected to match the VCC of the
MSP430, which is regulated to by the TPS77033 to 3.300 V (3300 millivolts). Each count is then
conveniently equal to 1 mV. In all cases, measured A/D value is ratio-metric to the MSP430 Vcc,
which drives the 1-bit DAC. For example, in the demonstration circuit regulated to 3.300 V, if the
A/D conversion code n were 1800 (out of 3300), this would indicate Vin has a value of exactly
50% of VCC or 1800 mV. In the final application, Vin must be limited to the common mode
range of comparator_A specified in the device data sheet.