I want to display one minute voltage change on analog voltmeter.
Voltage change: from -0.5V/min to +0.5V/min.
My analog voltmeter has 0-10V scale (I will replace it with homemade printed scale).
I don't want to use any microcontroller, PWM etc.
I want to learn how to do it by using op-amps and single supply.
In future - I want to scale it logarithmically (-0.5, -0.05, -0.005, 0, +0.005, +0.05, +0.5), but for now - let's assume that I need just linear delta-V read.
WHAT I KNOW FOR NOW
I know that I need active differentiator block. I can use formula from Wikipedia, find resistor and capacitor value. After that block I can use some non-inverting block to amplify voltage to desired range and add 5V with summing amplifier block to have 0V/min at the center of my voltmeter scale.
WHAT IS MY PROBLEM
My problem is single supply. When voltage change will be negative - I guess single supply op-amp will not work properly.
How can I deal with that?
Long time ago I was bored and I built custom thermometer that measures water temperature at the output pipe of old central heating furnace. It is supposed to inform me about temperature and temperature change. I can see how fast temperature is rising or dropping, and I can estimate when I should go to basement and put some logs or coal into furnace.
There is analog LM35 temperature to voltage converter (linear, 10mV/°C), microcontroller with 10-bit ADC with high oversampling and low pass filter at input.
Display looks like this:
I realize that 0.01°C resolution for temperature read is huge overkill and my thermometer acurracy is about +/- 1°C, so please don't comment that.
Now I want to build analog version of this and use two analog voltmeters similar to this:
One will show temperature, another temperature change.