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ADC imageDear all, I am using below model for reading analog value. I wanted to measure 0-10VDc &0-30Vdc .i wanted use it application where accuracy important. if i wanted to 12/16bit resolution of value weather above ckt work out.

Channel-1+ & channel - should be given in range of 0-5V through voltage divider network vout=(VsR2)(R1+R2) -> R1=R2=1K Vs=0-10V from DC output/sensor If it is 0-30V dc vout=(VsR2)(R1+R2) -> R1=5K R2=10K Vs=0-30V from DC output/sensor Is it correct ??

Using voltage divider network we can measure voltage . But how can measure using MCP series module.Is there any proven Schmatic to test it out.

Rasberry module

Ajit N
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  • As you need to change scales you might want to look into the Programmable Gain stage on the MCP3424, this would then let you select the range in software with out having to change the circuit components. For example 30v FSD at x1 and down to 3.75v FSD at x8. – Roger Jones Jun 12 '19 at 10:16
  • Yes, this MCP3234 and ADS1256 ADC with 5V Vcc can do -2.048V to +2.048V (full range 4.096V) and also have Programming Gain Amplifier. To measure 0~30V, we can use a resistive voltage divider to divide down 0~4.096V, and at the same time use an differential opAmp to shift down to -2.048V to +2.048V. Then we can make use of the full range. For 0~10V, we can use the same voltage divider/shifter, if we don't mind losing accuracy/resolution. I am new to this kind of new generation ADC. So I am only messing around as an hobbyist, with little confidence that I am doing the right thing. – tlfong01 Jun 12 '19 at 13:43
  • One problem with MCP3424 is that the voltage reference is built into the chip, and so the full range is fixed at is about -2V to +2V. For ADS1256, the user can select the negative and positive voltage references, to set the full range at 0~5V say, and this suits the OP's situation of all positive value measurements better. – tlfong01 Jun 13 '19 at 01:40

2 Answers2

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The circuit you show appears to be using I²C. However this shows pullup to 5V!

Connecting GPIO to 5V will destroy the Pi!

You can drive I²C from the Pi; it includes on-board pullup, so NO EXTERNAL PULLUP are needed. If they are present they NEED to be removed.

The resistors R1, R2 have NOTHING to do with a voltage divider. You will need to supply your own circuitry.

No idea what the block in the bottom RH corner is supposed to be.

Milliways
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  • thanks for suggestion. Is there any proven Circuit so i wont end up rasberry pi destroying. how i should give input in this case.There is no information on calculation of resistor selection for input. – Ajit N Jun 12 '19 at 08:48
  • @AjitN I was just addressing the Pi interface issues. Provided you remove any external pullups it will be safe. The input circuitry is not a Pi issue, and is unanswerable without additional detail; it depends on the input impedance of the ADC and the source impedance of what you are measuring. I doubt that a differential ADC is the best device (also why use a 4 ch device). You should ask on an EE site with detail of what you are trying to measure. NOTE there is an order of magnitude difference between 12 & 16 bit. – Milliways Jun 12 '19 at 09:35
  • I think the mystery block in the schematic is a bank of two DIP switches for selecting the I2C bus address. – Roger Jones Jun 12 '19 at 10:04
  • @Roger Jones - yes, the direct translation of the 5 Chinese characters is "double throw code switch" for AD0, AD1 pins to select I2C device addresses 01, 01, 10, 11. – tlfong01 Jun 12 '19 at 11:58
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Question

  1. MCP3424 ADC 0~10VDC, 0~30 VDC, 12/16 bit resolution

  2. Sensor Output Divider - 10V x 1k/(1k + 1k) = 5V, 30V x 5k/(5k + 10K) = 5V OK?

Answer

  1. No problem at all. You can even do 18 bit resolution.

  2. Using resistive voltage divider might not be a good idea, especially if you want high resolution. Perhaps you should consider a high impedance OpAmp instead of simple resistor divider. MCP3424 full scale input is -2.04V to +2.04v, not 0~5V. So your resistor values might not apply.

References

MCP3424 ADC-4 Digital I2C Channel Conversion Module for Raspberry Pi for Arduino 2.7-5.5 V High Precision - US$4

MCP3424 Schematic

MCP3424 Datasheet - Microchip

ADS1256 SPI 24 bit ΔΣ ADC Engineering Experimention Notes - tlfong01

Sending I2C-bus signals via long communications cables AN10658 — NXP 2008feb26

I2C Cable Length and Type - Rpi StckExch Discussions

MCP3008 Analog Input Resistive Voltage Divider Discussion - Rpi StackExchange

OpAmp Input Voltage Divider Discussion - Electronics Stack Exchange

Appendices

Appendix A - MCP3424 Summary

Four Differential Channels

Two conversion modes - One-Shot mode, Continuous mode

Auto-calibration internal offset and gain each conversion

Programmable Gain Amplifier x 1, x 2, x 4, x 8 (error: 0.05%)

On board 2.048V reference - Full-range - 2.048V ~ +2.048V

Programmable Resolution: 12, 14, 16, 18 bits

Programmable data rate: 3.75 ~ 240 sps

Appendix B - GY-MCP3424 Module

gy-mcp3424 module

Appendix C - MCP3424 Module Schematic

mcp3424 schematic

Appendix D - MCP3424 Analog Input Block Diagram

mcp3424 analog input

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tlfong01
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