Page 110 - Programming the Photon Getting Started With the Internet of Things
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Figure 5.8 Voltage divider circuit.
Figure 5.8 shows two resistors set up in series to one another between the input
voltage and ground. You can also see one wire coming from between both resistors, which
is the voltage output, which is the value that we read from the input on our Photon board.
If we first consider a fixed voltage divider, we can understand the concept of how a
voltage divider works. The mathematical calculation for working out the values of a
voltage divider is as follows:
V = Vin(R2 / (R1 + R2))
out
In our case, the voltage input from the Photon would be 3V3 and the voltage output
would be connected to one of the analog input pins on the Photon board. If we use the
resistor values for R1 and R2 so that they are matched (both 10 K in this example), the
3V3 is divided by 2 to make an output voltage of 1.65 V according to the equation. Let’s
look at this in a bit more detail by adding our values to the following equation:
