Amplying a small DC voltage difference

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1

Hello SparkFun forums. I’m afraid I have to ask a simple question after exhausting online resources.

I have a sensor that, under normal conditions, sees a max voltage change of ~5mV. I’d like to amplify that by at least an order of magnitude if not more. I’ve looked into wheastone bridges, differential amplifiers, and common emitter amplifiers but I always hit the same problem: the amplification saturates at the supply voltage. A lot of the resources online show AC voltage, but my application is DC voltage.

Specifically, I’m trying to amplify voltage using the common-emitter amplifier circuit attached to this message. The transistor is the [BC337 from SparkFun.

20210218_165537.jpg
20210218_165537.jpg4032×1960 1.03 MB

“Rpot” is the resistance of a potentiometer. My goal is to change the voltage at the collector (Vc), by changing the resistance of the potentiometer. Problem is, no matter the voltage at the base (Vb), Vc is always the power supply’s voltage (9V in the picture attached).

I’m sure there is something fundamentally wrong with my understanding of voltage amplifiers and the solution is trivial, but I just can’t see it.

tl;dr

How do I amplify a small ~1mV DC signal to 10-100mV?](https://www.sparkfun.com/products/13689)

2

You might consider an OP-AMP, there’s tons of tutorials online that can walk you through how to use them.

https://www.youtube.com/watch?v=bc8YrxqhtJo

3

Op Amps were what I first tried and I could not get the circuit to respond to the sensor as i wanted. Specifically, I tried circuit outlined in Figure 1 on TI’s [Operational amplifier gain stability

Are Op Amps the most beginner friendly way to amplify a DC signal? If not what would you suggest?](https://www.ti.com/lit/an/slyt374/slyt374.pdf?ts=1613772718222)

4

Probably the easiest way to do what you want to do, this book might help.

http://www.zpag.net/Electroniques/Kit/R … rcuits.pdf

5

What’s the value of the potentiometer in the drawing?

6

I’m sure there is something fundamentally wrong with my understanding of voltage amplifiers and the solution is trivial, but I just can’t see it.

Since the circuit you posted is incomplete, we can’t either.

To address the immediate problem, supply more information.

Which transistor: PNP or NPN and identifier?

Which is the emitter and which is the collector?

What is the value of the resistor between Vc and 9V?

What is the value of the pot connected between the base and GND?

To address the real problem, use an op amp, or preferably a differential amplifer, like one of the INA series from Texas Instruments.

Basics on op amp voltage amplifiers, from TI: https://www.ti.com/lit/an/sloa097/sloa097.pdf

7

Post is old but I ended up using the HX711: https://www.sparkfun.com/products/13879