How Can I Invert and Amplify the Output of a Rangefinder for Robotics?

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Discussion Overview

The discussion revolves around the design of a circuit to invert and amplify the output of a rangefinder for use in robotics. Participants explore the requirements for converting the rangefinder's analog output, which varies with distance, into a voltage signal suitable for driving a motor. The focus is on achieving a higher voltage output for farther distances and a lower voltage for closer distances, with considerations for component selection and circuit configuration.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant describes their goal of using a rangefinder with an analog output to control a motor, seeking to invert and multiply the output voltage.
  • Another participant questions the meaning of "multiply" and clarifies the desired output range, suggesting a simple op-amp inverting configuration with a specific gain.
  • A participant explains that the sensor outputs a lower voltage for farther distances and a higher voltage for closer distances, detailing the desired relationship between sensor output and motor voltage.
  • One suggestion involves using a dual op-amp configuration, emphasizing the importance of selecting appropriate op-amps and power supplies for the circuit.
  • Another participant expresses gratitude for the detailed explanation and acknowledges their limited knowledge in electronics.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the specific circuit design or components to use, and multiple approaches are discussed without resolution. There is uncertainty regarding the exact requirements for the motor and the characteristics of the rangefinder output.

Contextual Notes

Participants mention various assumptions about the voltage ranges and the need for specific op-amp configurations, but these details remain unresolved. The discussion also reflects a lack of clarity on the motor specifications and the timing requirements for voltage changes.

BigSteve
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Hi folks.
I am ME/AE by profession but I love robotics and I tinker. I have pretty much zero EE experience so this question probably has a simple answer, I just don't know where to look.
Basically i will have a rangefinder with an analog output. I want to invert and multiply that output. So that farther readings will result in higher voltage to a motor. Also, the multiplication will be very small, like 5V to 12V.
Thanks.
 
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BigSteve said:
Hi folks.
I am ME/AE by profession but I love robotics and I tinker. I have pretty much zero EE experience so this question probably has a simple answer, I just don't know where to look.
Basically i will have a rangefinder with an analog output. I want to invert and multiply that output. So that farther readings will result in higher voltage to a motor. Also, the multiplication will be very small, like 5V to 12V.
Thanks.

Is multiply mean gain to you? Is the input 0 to +5V and you want the output 0 to -12V?

What speed is the voltage change? What is the driving requirement of the motor that the circuit has to drive? What I mean is how much current you need to drive the motor.

Usually all you need is a simple op-amp inverting configuration with a gain of -12/5 = -2.4 if that is what you meant but multiply.
 
Yeah, I probably didn't explain that quite right.
My sensor will output a voltage based on distance. For farther distances it will output a lower positive voltage, but I need a high (still positive) voltage to the motor. Close objects will out put a higher voltage, but I will want a lower(still positive) voltage to the motor. So a close object will approach 5v and the motor voltage should approach 0v, then a far object will approach 0v and the motor voltage will approach 12v (or whatever max motor voltage ends up being).
I don't know about motor current because I haven't purchased a motor yet. I was trying to get the design more concrete before I did. I was thinking of a 12vdc scooter motor or something similar.
Voltage change doesn't need to be anything particularly quick.
 
This is one way to do this:

25tx7ic.jpg


Input from 5V to 0V will give output of 0V to 12V. This is my understanding.

Use a dual op-amp. If you can find a rail to rail input and output op-amp, you need only a single +12V power supply. But if you have +/-15V supply, then any dual op-amp like TLO82 etc will work.

You can do it with a single op-amp, but the resistors are going to be harder to match and op-amps are cheap. I called for 5V reference driving the resistor divider just for convience. I need a +2.5V at the +ve input of the first op-amp, however which way you want to get it is up to you.
 
yungman said:
This is one way to do this:

25tx7ic.jpg


Input from 5V to 0V will give output of 0V to 12V. This is my understanding.

Use a dual op-amp. If you can find a rail to rail input and output op-amp, you need only a single +12V power supply. But if you have +/-15V supply, then any dual op-amp like TLO82 etc will work.

You can do it with a single op-amp, but the resistors are going to be harder to match and op-amps are cheap. I called for 5V reference driving the resistor divider just for convience. I need a +2.5V at the +ve input of the first op-amp, however which way you want to get it is up to you.
Thank you for the detailed answer. I probably could have never gotten that far on my own.
 
BigSteve said:
Thank you for the detailed answer. I probably could have never gotten that far on my own.

You are welcome. If you have further question, I'll be happy to help.
 

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