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I'm trying to digitize a Hall Sensor whose center voltage is 2.5V and the gain it's output is 1.5V to 3.5V, or ±1V. My digitizing card's center voltage is 0V and I would like to get the full range of the sensor in the 0V space, -1V to +1V. I'm using a LM358 op amp to try to do the task. I'm very new to building circuits and I really don't know where to start.

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  • \$\begingroup\$ What supply rails are available from the digitizing card? \$\endgroup\$
    – scorpdaddy
    May 20, 2019 at 2:23
  • \$\begingroup\$ There are no voltages coming from the card at all. It is only data in. Here's the card: signatec.com/products/daq/… \$\endgroup\$ May 20, 2019 at 4:17
  • \$\begingroup\$ I've been using USB to power the sensor and the amp, but I'm realizing that 5-0V isn't going to cut it. I was thinking that I'd invert the +5V for input into the amplifier and still be able to use a common source to power both the sensor and the amplifier. \$\endgroup\$ May 20, 2019 at 4:22

2 Answers 2

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You can do this:

schematic

simulate this circuit – Schematic created using CircuitLab

Note that the op-amp requires +/- supplies. You can generate the negative supply from your +5V supply using an ICL7660 and a few ceramic or electrolytic capacitors. Not shown are supply bypass capacitors.

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    \$\begingroup\$ @ Spehro I like it. \$\endgroup\$ May 20, 2019 at 10:59
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    \$\begingroup\$ @ Spehro I built the circuit and it worked great. I ended up using an ATX power supply for the ±5V source. \$\endgroup\$ May 22, 2019 at 14:09
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So you want to take in 1.5 to 3.5v, and output the same change in voltage but shifted down to swing +-1volt.

How about this [notice we don't need a calculator to design this]

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ I also built your circuit and it worked great. Your explanation was very clear and I learned a lot from it. Thank you. \$\endgroup\$ May 22, 2019 at 14:11
  • \$\begingroup\$ I have another problem. Both circuits worked as advertised, but I can only upvote one of the two. Somehow that doesn't seem fair. Thank you both again for helping me out. \$\endgroup\$ May 22, 2019 at 14:16
  • \$\begingroup\$ @ bgeorge98121 Upvote Spehro answer. But before you upvote it, be sure you understand its elegance What he did is useful in many situations. \$\endgroup\$ May 24, 2019 at 3:49

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