OP-AMP VOLTAGE-DIFFERENCE AMPLIFIER CIRCUIT

182

03:12:33

I need a simple, compact way to send Arduino a voltage signal proportional to a potentiometer (pot) position.  The issue is that the1K pot installed is a 10-turn and the angle traveled is only about 70 deg so ~2% of the 1K range (about 20 ohm change).  Arduino 5V is sent to the pot input (about 3 feet away) and also to this small circuit near the Pot.   The pot is set at one end of travel and the near 0 ohm end (1%=10ohm).  The OP AMP takes the difference between the Arduino 5V  and the pot output voltage and also then amplifies this difference by about 30X.  This results in a voltage output back to the Arduino (represented by the Voltmeter) of 0 to 4.4 volts proportional to the pot position of 1% to 3%.  Try it by changing the pot % position settings.  The 1K resistor to the voltmeter is a current-limit safety.  NOT SHOWN: Vcc+ is also connected to +5V and Vcc- is connected to ground. Oh, and I plan to use trim pots for the 716 & 399 ohm resistors as getting 0 volts when the pot is near 0 ohms is balancing act of these two guys.
REV 1: Realized that the output was inverted.  Added inverting OP AMP with gain of 1 to correct this.  Using a TI NE5532 chip which has 2 OP AMPs built in, so this works fine.  Eliminated the capacitor also - don't think it's needed.

published 8 years ago

2ctiby

8 years ago

Would it help to attach a second pot and leave the first pot alone in a suitable fixed setting. You could then map your easy-to-manage new full scale pot range in an Arduino program to your required output. http://everycircuit.com/circuit/5078124907986944

Weedster

8 years ago

This is an interesting idea. I'm thinking about whether I can squeeze a second pot into the area of the is rotation sensing pot - not sure I can fit one in this very right space. I am also considering ripping-out the 10-turn pot and replacing it with a 1-turn which directly solves this issue without the amplifier circuit. Thanks for the idea!

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.