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I want to convert a 24V signal from sensors to 3.3V input signal for a Raspberry Pi. I have almost 20 sensors, so I have to convert all to 3.3V.

Is there any IC from which I can do multiple voltage conversions coming from many sensors? What is the additional ckt to used, to remove the floating value of input?

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    Is this an analog signal? or Digital? – Steve Robillard Dec 1 '15 at 6:04
  • digital signal . High and Low – amrit kumbhakar Dec 1 '15 at 12:38
  • What do you mean by "ckt"? Do you mean "circuitry"? – Greenonline Feb 8 '16 at 17:42
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Here is a simple voltage divider circuit that should meet your requirements - note that the upper resistor will be sinking nearly half a watt when the input is 24V so should be 0.5W rating - 0.6W is a common rating for some manufacturers so should be easy to source...

This will draw over 2 milliamps with a 24V input voltage if that is important for the circuit under test.

Simple voltage divider using a 10K resistor in upper arm and 1.5K in lower to divide 24 volts DC down to 3.1 volts to feed into a GPIO pin on an RPi

Drawn using GSchem, part of the GPLed GNU Geda package.

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    I know the OP talks about external signal but I think its worth mentioning that sending data BACK to the sensor is not possible with this circuit. PS Did you know Pi Exchange has a schematic editor now? – Piotr Kula Feb 17 '16 at 17:46
  • The OP did mention "input signals" so I took that to mean sending data back is NOT wanted - so it is a valid answer - though your point is valid for anyone seeking a bi-directional level conversion - it is possible but it needs active (semiconductor) devices. PS Yeah I know about the schematics editor but I keep my web-browser locked down with NoScript and RequestPolicy and I wasn't keen to jump through the additional hoops to get all the JavaScript working to use it - when I have a perfectly good schematic editor installed and in use - though it does mean posting "dumb" pictures...! 8-P – SlySven Feb 19 '16 at 3:54
  • Hi, not critisizing that your answer was wrong or anything. I think its a great answer - Just wanted to alert you and other that it doesn't support sending signals back thats all. OK, cool, it sounds like you locked down tightly on your side ;) I jsut block flash for now, not had any issues since flash ads stopped showing on my side. But thanks, even pictures are amazing to add to content. – Piotr Kula Feb 19 '16 at 14:36
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That's a hardware question, not a RPi question.

Use two resistors for each sensor to make a voltage divider. A calculator like this will help you get the right values, and it includes a picture of how to hook it up. If the resistors get hot from the current, then you need bigger ones, or you need to use a different method.

Here is a good discussion of Optocouplers

  • Could you expand your answer to explain how the optocouplers would help? Also, as links are liable to die over time, could you provide a synopsis of the link? – Greenonline Feb 18 '16 at 23:12

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