Scan Resistors with ScanR

Scan Resistors with ScanR

Ever messed with resistors? They’re electrical components that limit the current in electrical circuits, basically making sure your TV can handle the voltage it gets when you plug it in. Failure to do so would likely result in tears due to your TV frying.

Each resistor has a different resistance value, indicated using color-coding:

"4-Band Resistor" by jjbeard - Made in Inkscape. Licensed under Public Domain via Commons -

There are usually four bands, but only the first three are required to calculate the resistance (measured in Ohms, Ω). To get the resistance, you simply put together the number represented by the first band (‘2’ for red) and the one represented by the second band (‘7’ for violet), then multiply this by a multiplier (green represents ‘5’, so the multiplier is 10⁵). The result is 27×10⁵, or 2,700,000 Ohms. It’s easy to do, but requires you to have a cheatsheet or memorize what the colors indicate… unless you have a handy app on your smartphone that does it for you.


That’s exactly the kind of app XDA Recognized Developer laufersteppenwolf has created, ScanR scans resistors using your device’s camera, and shows you their resistance. It’s very simple to use simply point your camera at a resistor, position it so that the blue line goes from the first band to the multiplier band and hit the “Scan” button. For extra precision, ScanR takes 20 scans at a time and uses the clearest image. If it still detects some colors incorrectly, you can easily correct it by manually selecting the correct color. ScanR also supports manually inputting band colors, as well as resistors with three “necessary” bands or four (hundreds, tens, units and tolerance bands). If you want to take a quick look at how it works, here’s a short video example:

ScanR is completely free and open source. You can check the source code on the ScanR GitHub repo, or visit the ScanR forum thread for more information and downloads. Feedback is welcome, so feel free to leave any suggestions in there for the developer.

About author


Currently studying for a Master's degree in Computer Science at EPFL, Germain Z. is interested in all things related to technology, mobiles and programming. Previously, he was also a Forum Moderator and Recognized Developer on the XDA forums.

We are reader supported. External links may earn us a commission.