Temperature Sensors.


Where does it make sense to use a rail to rail operational amplifier, if they never use it? Okay, with a gain of two, using the inverting input, you can cancel out the DC voltage between the resistor and the thermistor. Yea, it takes a second voltage divider but, since the gain is two, all of the readings change appropriately. So, it's the same math but, it's literally driven from 0-1052, or 0 to 5 volts.

I was dinking around with circuit board, and it has a threshold control Potentiometer, and it doesn't even make sense to include the Operational Amplifier. It's a higher resolution, without changing the sensor, and using the same SGM358YS chip. I just don't understand how or why they are not using the instrumentation amplifier and common mode rejection to fix the scale. Once it's all said in done, in your code, you'd have to divide the Analog Read Value by two, and that's only real change. Even though your integers are cut in half, you still get point five, on the floating end.

Just starting at half on, cuts your resolution because, those binary bits won't change, and only change matters.

I don't understand why they throw out the analog electronics before the design digital circuits?

You'd be using an Operational Amplifier, in a Differential Amplifier Circuit, with a gain of two on the line in from the sensor's voltage divider.

Using the SGM358YS as a Differential Amplifier

It sounds like you're describing a temperature sensor module that is frequently sold in a pack with other modules as "starter kits" or such for the Arduino. If that's the case then the layout and components on the board are the way they are because the boards are treated as generic and used with several different types of sensors - piezo mics, flame sensors, etc.