Is it possible to get a decreasing output voltage from an increasing input voltage?

Thread Starter

PushToClose

Joined Aug 5, 2021
16
I need to take a hall sensor input, and get an output signal voltage which decreases as the input voltage increases, with a linear relationship between the two. Is this possible? I can't work out how I could achieve it.

Circuit voltage is 5V. The Hall input range is 0.8 - 4.2V. I need to produce an output range starting at 2.5V and going down to 1.1V. Any ideas for where to start experimenting?

Thanks for any assistance.
 

Thread Starter

PushToClose

Joined Aug 5, 2021
16
Thanks for the replies, that's incredibly helpful! May I ask some follow up questions?

- I already have some LM6484 op amps. Looking at the data for the CA3140 they don't seem massively different - could I achieve the same aim with a different basic op amp, or is there a feature of the CA3140 that is essential? (I appreciate that small specification changes probably make a large difference to behaviour, but I don't fully understand it yet)

- What is the need for the POTs instead of just a voltage divider?

- Lastly, to test how well I've understood op amps so far, is it a voltage follower inputting into a differential amplifier?

Thanks again.
 

ericgibbs

Joined Jan 29, 2010
14,697
hi,
If the LM6484 op amps can operate from a single 5V supply they should be OK.

The voltage follower is used to reduce the incoming Hall signal, it also provides a low impedance connection for the following Gain of 1 Amplifier Inverting resistor.

R5 and R6 apply a positive offset voltage to the Non inverting input, which has a Gain of 2.

You need a 100K pot at the Span and Zero in order to adjust out any Vout errors due to component tolerances.

Do you follow, OK.?
E


Update, added image.
Set the pots to approx 50% before powering up.
to Calibrate, Vhall input at EG 986.png0.2V and 4.8V
EG 986.png
 
Last edited:

Thread Starter

PushToClose

Joined Aug 5, 2021
16
This is great, I really appreciate you taking the time to help. Thanks for the explanation - it has been a long time since I studied this stuff. I'm not sure I understood it then!
 
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