# Question about op-camp circuit

• atlbraves49
In summary, this is the op-amp circuit I'm going to have to implement...This is an op-amp circuit. It is meant to be used to amplify signals. It has a power supply that provides -9V and 9V, and a drive voltage of -5V. It uses a zener diode to create a reference voltage, and a resistor to create a voltage drop.
atlbraves49
so this is the op-amp circuit I'm going to have to implement...

http://www.tekscan.com/images/flexi-circuit-new.jpg

Does that mean I need a power supply to power the supply voltages of -9V and 9V, and then another power supply to power the drive voltage of -5V?

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Why not use a 5.1 V Zener between ground and V(t), and a resistor between V(t) and -9 V?

skeptic2 said:
Why not use a 5.1 V Zener between ground and V(t), and a resistor between V(t) and -9 V?

could you explain more about the zener? (and the resistor between V(t) and -9V should work, thanks)

Zener diodes are reversed biased diodes that conduct at specific voltages. They come in a variety of voltages usually the same as the 10% resistor values. Zeners below about 4 V are of a different type and their voltages are not as stable as those above that value. The actual voltage varies a little not only from unit to unit but also due to the amount of current they are conducting and their temperature.

Zeners come in various wattages so you will need to pay attention to how much current they are conducting and how much power they are dissipating.

For your circuit you would connect the Zener's cathode, the end marked with a band, to ground and the other end to V(t). For starters you might try using a 1 K resistor from the Zener anode to -9 V. Note: If you connect the Zener in backwards it will work like a diode and the voltage drop will be about 0.65 V instead of 5.1 V.

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so something like this (just to make sure I am understanding the setup)?
http://img443.imageshack.us/img443/3008/opampuu6.jpg

And is there a reason you can't just put a resistor between the -9V and -5V to get the voltage drop of 4V across the resistor? Like, why is the zener diode even needed?

Last edited by a moderator:
You're right, you don't really need the Zener (your diagram was correct, however). You could do it with a resistive voltage divider, especially because the Flexiforce is such high resistance. Keep the resistances at less than 1/10th of the lowest value you expect to see with the Flexiforce.

Consider decoupling that -5V reference voltage with capacitors to lower the impedance of that reference.

i guess it depends on how accurate you need things. zeners are generally crap as a reference. you can get some noise coupled through the power supply with an op-amp, and you want to put some capacitors on the power inputs near the device... but overall, probably more error is introduced directly via Vt.

edit: if you measured both Vt and Vout to compute each measurement, i don't guess it would matter much.

You will need to calibrate the amplifier/sensor with some sort of standard forces applied to the sensor. What are you requirements? If you want really good results, you could use NIST traceable weights as your calibration standards (only for small values of force; cost prohibitive for large weights).

## 1. What is an op-amp circuit?

An op-amp circuit, short for operational amplifier circuit, is a type of electronic circuit that uses an operational amplifier to amplify and manipulate electrical signals. It is commonly used in signal processing, filtering, and amplification applications.

## 2. How does an op-amp circuit work?

An op-amp circuit works by amplifying the difference between its two input terminals. The output is then fed back to one of the input terminals to create a closed loop. This feedback allows the op-amp to have a very high gain, making it useful for amplifying small signals.

## 3. What are the main components of an op-amp circuit?

The main components of an op-amp circuit include the operational amplifier itself, resistors, capacitors, and power supply. Depending on the specific circuit, other components such as diodes, transistors, and inductors may also be used.

## 4. What are the different types of op-amp circuits?

There are several types of op-amp circuits, including inverting amplifiers, non-inverting amplifiers, differential amplifiers, summing amplifiers, and integrators. Each type has a different configuration and is used for different applications.

## 5. What are the advantages of using op-amp circuits?

Op-amp circuits have many advantages, including high gain, high input impedance, low output impedance, and low distortion. They are also versatile and can be used in a wide range of applications, making them a popular choice for electronic circuits.

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