Basic Electronics for Tomorrow's Inventors by Nick Dossis

Author:Nick Dossis
Language: eng
Format: epub
Tags: -
Publisher: McGraw-Hill Companies, Inc.
Published: 2012-11-11T16:00:00+00:00

FIGURE 9-3 A potential divider circuit

This type of circuit allows you to generate a specific output voltage by altering the values of the resistors. You can use this formula to calculate the output voltage:

Output Voltage = Input Voltage × (R2 / (R1 + R2))

So, for example, suppose that R1 and R2 are both 4.7KΩ, and that the input voltage (the supply voltage) is 4.5 volts. If you add these values to the formula, you can calculate the output voltage as follows:

Output Voltage = 4.5V × (4.7KΩ / (4.7KΩ + 4.7KΩ))

Output Voltage = 4.5V × (4.7KΩ / 9.4KΩ)

Output Voltage = 4.5V × 0.5

Output Voltage = 2.25V

So you can see from this calculation that the output voltage is half the input voltage when the values of R1 and R2 are equal.

Let’s see what happens if you reduce the value of resistor R1 to 1KΩ and keep the value of R2 as 4.7KΩ.

Output Voltage = 4.5V × (4.7KΩ / (1KΩ + 4.7KΩ))

Output Voltage = 4.5V × (4.7KΩ / (5.7KΩ)

Output Voltage = 4.5V × 0.82

Output Voltage = 3.69V

This exercise shows you that you can increase the output voltage by reducing the resistance value of R1. Now that you understand this concept, you can put this circuit effect into good use in this experiment.

The Circuit Diagram

Have a look at the circuit diagram for the temperature sensor, shown in Figure 9-4. The circuit should now look familiar to you, because it uses the potential divider that you just read about.

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