A project log for World's Worst Programmable Gain Amplifier

Building a programmable gain amplifier by applying PWM controlled LED light to an LDR in an inverting amplifier

Jake WachlinJake Wachlin 01/21/2020 at 02:150 Comments

To prove the idea, I set up an inverting amplifier. I used a TLV2462 operational amplifier, since that is what I had on hand. This has a gain-bandwidth product of 6.5MHz, and rail-to-rail output. I planned to put a roughly 500Hz square wave out of an Arduino PWM through it, so this was good enough.

The gain here was:

The resistance from the LDR ranged roughly from 1k to 13k from dark to bright LED flashlight onto it. The second LED I had was 200 Ohm, so the amplifier had below unity gain. I drove the LED with a PWM of frequency roughly 60kHz, and ramped through its 8-bits of resolution. Looking at the output on the scope, it works!

So, yes, it does work, its janky, but maybe someone would have a use for it.