LED Tester

Hey everyone, I build a lot of LED based projects and always find it cumbersome to test the LED's before using them in the project as I've learnt it the hard way of replacing the LED's after finishing the projects only to realize some of them are bad.

It was meant to be a very simple build however I have this habit of overcomplicating things and so here is an LED tester which can be used for regular single colored as well as Common Anode and Common Cathode LED's.

It also has color specific resistors inside so they can be tested safely without damaging the LED's and the device works of 2 x AA batteries which are easily available with everyone and will last a long time for this project.

Let's get started

• An old power bank or enclosure which can house all these components
• 3 way switch or 3 position switch
• 3.3v boost module
• Female headers
• 2 x AA batteries + battery holder
• Small piece of perf board
• 10 ohm x 3, 100 ohm x 1 resistors

So I found this little bugger in my box of junk and thought would be useful here. This is not an important part of the project but having a fixed supply voltage will help in deciding the suitable resistors.

An alternate option is to use the 2 x AA batteries directly and choose the resistors on an approximation, LED's are quite versatile and don't need the resistors value to be exact.

Coming to my choice of the resistors, they are what I had and they work well with the 3.3 supply voltage that am giving them and the current can vary from 10ma - 20ma for any color. But you can choose them based of your availability, this is how I calculated the resistors for this project.

Red/Yellow/Orange LED - Forward Voltage 2v

Green - Forward Voltage 3v

Blue/Violet/White - Forward Voltage 3.2v

R= (Vs - Vf)/I where Vs - Supply voltage, Vf - Forward voltage of LED, I - is the current required for the LED

This is an optional step. I'd like my device to look clean and functional and last a while

Found this old dead power bank , removed its internals and this looks like a perfect enclosure for my need.

The front has a small opening where it had a button so I plan to put in the female headers here and glue it up.

On the side you can make a cut out for the switch. Moving onto the inside there was enough space for a 9V or 2 AA or 3AAA batteries or even a 18650 cell. I chose the 2 x AA as i had a holder and these batteries are pretty cheap and the design of this box is such that the top half joins to the bottom half with a clip and so it can be opened, batteries added when ever needed.

There is small area above the battery compartment which is more than sufficient for my circuit. I cut out a perf board to match the shape of the space.

The most interesting part for me at least. Am still a novice when it comes to soldering correctly and neatly, so pardon my ugly soldering skill

Bend the female header to a right angle so that it does not push into the batteries when closed and add small pieces of heat shrink tube as the contacts are very close to each other.

The 3 position switch is a DPDT meaning the switch contains two input terminals and each of them moves between their own two output terminals. Cross join the outer terminals and the middle 2 pins connect to the common pin of the female header and the other to the common connection of the resistors. Please follow the connection diagram if it feels confusing.

After soldering the components , glue the perf board, battery solder, switch and the female headers.

Please watch the video to understand how it all works. It is a useful design for me and will serve a long time.

Thanks for your interest, Stay Safe Stay Happy.