Minty LED Tester





Introduction: Minty LED Tester

Stop fumbling around for a 3V battery, build your own LED tester, and freshen your breath while you are at it!

Let's get started.

Step 1: Materials

You will need:

Step 2: Individualize the Wire Headers

Find the two metal wire headers, and fold them back and forth until they are apart.  In order for these to fit in the plastic housing, you will have to take some wire cutters and trim the edges of the header. 

In the picture below, I have noted what you will need to trim off on the headers in order for them to fit in the housing.

Step 3: Some Soldering

Take your first piece of hookup wire, and solder it to the portion of the wire header that has a lane for the wire to rest in.  Solder that wire down, and then if you can, crimp it.

Do the same for the other wire header as well.  You should now have two wire headers with two pieces of hookup wire attached to them.

Step 4: Some More Soldering

Now solder the opposite end of each hookup wire, to leads (or holes) on your 3V Coin Cell Battery Holder.  Make sure the 3V battery is not in the holder during this step!

Since most of the LEDs that I use are safe with just the 3V battery, I did not add a resistor.  But if you have LEDs with a lower voltage drop, then there is definitely enough room inside to add a resistor. To add a low Ohmage resistor, connect it between the negative lead on your battery holder, and the wire header thatis connected to that piece of hookup wire.

Step 5: Drilling and Securing

Now take your rotary tool and drill a hole roughly 75% of the total circumfrence of your rubber grommet.  Drill one small hole intially, and then, as needed, make the hole bigger so that you can easily but snugly fit your rubber grommet in the hole.

The rubber grommet (for those who don't know) should have one half sitting on top of the Altoids tin, and one half sitting on the other side. 

Now take your metal wire headers, and place them into each hole on the plastic, white wire housing.  You should be inserting the headers into the side that has the pattern set for the headers.  (Not the side with just the rectangles.) 

Be sure that the headers are securely fastened inside of the plastic header.

Now take the plastic header, and poke it through the rubber grommet on the Altoids tin.  The side with just the rectangles should be facing outwards. 

Step 6: Testing

Insert a 3V coin cell battery into the battery holder, secure everything inside of the tin, close the tin, and you are done!

Find an LED with a forward voltage of around 3V, and test it in your new Minty LED Tester!



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    awesome i need one! got to start making☺

    That's very Ingenious!

    cool idea. But the problem is some red and IR led works on 1.5V or 1.2V. That means the 3V cell may given them a sudden death because of the large current. But a single resistor will solve the problem. I think hundreds ohms will do.

    6 replies

    maybe, but most red and ir leds are 3.6v ones, so you should be safe.

    May be the leds you find is more than one in serial. The longer the wavelength, the lower voltage the led needs. Of course the leds from different manufacture may work at a slightly different voltage. But the error can hardly exceed 20%.

    Since there is so much extra space in the tin, one could set up 2-3 sockets and have different resistor values on each to provide lower current to the other sockets....then you could "start" at the lower end and if it doesn't light move up to the next higher level until the LED lights or is proven defective.

    Same current...lower voltage. 1.8 - 2.0 for Red/Orange 3.0 -3.2 for Blue/UV/Green

    Hmm, then in stead of current limiting resistors, one could set up "voltage dividers".

    Correct.... So lets say you have a perfect 12V source. If you would like to achieve 3V across one resistor and 1.8V across another @ .025A (25mA) you would do something like this: V=IR 12V=(.025A)(R) Total resistance of the circuit = R = 480 ohms To achieve 3 V across one of the resistor the value of the resistor must be: R1=3V / .025A R1= 120 ohms To achieve 1.8 V across one of the resistor the value of the resistor must be: R2=1.8V / .025A R2= 72 ohms Total R must equal 480 so.... 480 = 120 + 72 + r So the value of 'r' (the last of the 3 resistors in this circuit) = r = 288 ohms then you make it so when your plug in an LED the current will bypass the resistor and flow through the LED and it would have no affect on the rest of the circuit. (Make sure you know the Amperage of the LED, it is vital to the circuit)

    Oooo, I see LOTS of potential with this one :-)

    I have a few extra LED tester kits lying around in my workshop. Send me a PM and I can hook you up with one.

    email me at thanks

    thats ok, making stuff is a lot more fun

    Great! A small project where I can finally recycle almost useless coin cell batery holders!

    Would there be room in there to add a 2nd battery and a resistor (270R or so)? If so, it would be a lot safer for the LEDs.  
    The 'voltage' of a LED isn't the voltage it's designed to run on, it's the voltage 'lost' inside the LED.  A typical red LED has a drop of 1.8V so the current through it from the 3V battery could possibly kill it.  A bit more info on LED voltage drops HERE.

    1 reply

    There is definitely room left inside of the tin. Most of the LEDs that I use are safe with the 3V, but you can mod this any way you wish.