[uncle_bob]

Step 5 - Signal Amplification

There are several ways of designing an amplifier based on operational amplifiers. In our case we chose one of the simplest forms, usually referred to as non-inverting amplifier which can be generically represented in the form illustrated in the figure below.



In this configuration the computation of the gain of the amplifier is obtained from the following formula:



Since the desired Vout is 1.1V and what our Vin is 0,160V our OP must have a gain to 6.875 (Vout / Vin), which we obtain with R1 = R2 = 8K Ohm and 47K Ohm.

The gain we want is quite modest for any OP, but probably will not serve in any one OP. Most of the OP power require a symmetric positive, or negative and GND. Since I'm not building a power just for the OP, but feed it 5V from the Arduino I have available, I will have to choose an OP that has this possibility, there are many and are designated by OP's Single-Supply.
Moreover matter me for future use, which is an OP able to provide a voltage very near the supply voltage output. These PBs are also of course, and are commonly referred to as OP's Rail-to-Rail. For this particular situation, my choice was to AD822AN - Single-Supply, Rail-to-Rail Low Power FET-Input Op Amp.

AD822AN APPLICATIONS
Battery-powered precision instrumentation
Photodiode preamps
Active filters 12-bit to 14-bit data acquisition systems Medical instrumentation
Low power references and regulators

We already have everything we need, the rest is now building.
At the end of this article a little example code for the Arduino that allows us to view our Solar Radiation readings will be presented.


Continued ... in the next topic.