Find all your DIY electronics in the MakerShed. 3D Printing, Kits, Arduino, Raspberry Pi, Books & more!

AskMake_Jameco.gif

Ask MAKE is a weekly column where we answer reader questions, like yours. Write them in to becky@makezine.com or drop us a line on Twitter. We can’t wait to tackle your conundrums!

Resistive_divider.png

Louis writes:

I’ve seen the term “voltage divider” used a lot lately. What exactly is a voltage divider, and what is it used for?

A voltage divider does what it sounds like: it creates an output voltage less than the input voltage. A potentiometer can be used as a voltage divider, as can two resistors in series. It’s often used as a reference voltage, where little current is drawn over the connection. Op-amps use reference voltages to change signal output, so you can use a pot as a voltage divider to change attributes of sound in a synthesizer, for example. The op-amp outputs current that is proportional to the difference in voltage between it’s two inputs, so the resistor divider is used to make the output voltage a multiple of the input voltage- basically a resistor divider in reverse.

Many sensors respond to their respective input by producing a corresponding change in resistance. For instance, a light sensor might have a high resistance when it’s bright out, and a low resistance in darkness. Sensors can be used in one of the positions pictured above (R1 or R2; the diagram is a resistive voltage divider) to invert the output. For example, a light-sensitive resistor (LDR) in a voltage divider could be changed from its normal high-when-light state to high-when-dark. Sure, you could invert that output in software, too, but what if you’re not using a programmable microcontroller? With just an extra resistor, you’ve inverted the sensor’s function.

Here’s some more reading material on voltage dividers:

Where do you use voltage dividers? Post up your experiences in the comments.

This week’s Ask MAKE has been sponsored by Jameco Electronics.

Becky Stern

Becky Stern is head of wearable electronics at Adafruit Industries. Her personal site: sternlab.org


Related

Comments

  1. Chris W says:

    My scariest divider is the 6666/1 divider in my CRT monitor. It provides a scaled sample of the CRT anode high voltage to the regulation circuit. If the “bottom” resistor fails then 27,500 volts are present on a low voltage wire+board.
    A designer caution: when designing voltage dividers be aware of the load which the output is connected to. It is usually in parallel with the “bottom” resistor.

In the Maker Shed