Introduction: Modifying an Inexpensive Laser Pointer Keychain for General Use

Nearly all of us have played with a laser pointer before, especially those of us who have cats. We at H3 Laboratories found these particular ones at a dollar store and put them to use on our power tool track project.

These keychains are powered by three LR41 coin cell batteries and have stated power of less than 5 mW. They also include a small white LED. The laser color is red, and they throw a round dot. Surprisingly, they include an adjustable lens.

This Instructable will show how to disassemble the keychain, modify the small PCB inside, and make it suitable for use as a project component.

Tools needed:

  • Wire strippers
  • Soldering iron & solder
  • Desoldering pump
  • Helping hands
  • Pliers
  • Cutters
  • Scissors
  • 2 conductor wire

Disclaimer: always take appropriate precautions when soldering and working with lasers.

Step 1: Disassembly

First, take the keychain out of the package. Put the batteries aside, you won't be needing them for this anymore.

Unscrew the cap where the chain is. Normally the batteries would go in here. Then hold the barrel so that the buttons are on the bottom and pull the other end off using pliers. The entire assembly should slide out, provided the buttons have settled out of the way. The barrel (which is normally part of the circuit) and the plastic battery retainer inside can be put aside. You should have parts that look like the second picture in this step.

Note that there are some insignificant parts variations on these. The PCBs are either green or blue, and the wire sheath on the LED lead can be red or blue. Neither of these changes anything, even though the PCB trace patterns vary slightly.

Step 2: Prepare to Desolder

We don't need the LED, so either clip it off or bend the leads back and forth near the board until the break off. Put the LED aside.

The two pictures here show the top (with the tactile buttons) and bottom (with the solder joints) of the PCB.

The battery contact spring and the buttons need to be removed. On the bottom is a 62 Ohm SMD resistor; we'll want to keep that in place, so don't damage it with too much heat.

Step 3: Desoldering

Melt the solder holding the battery spring on, and pull the spring off using pliers.

Some of the button contacts may not be soldered,or at least not very well. Desolder each joint and remove the buttons.

Finally, desolder the stubs of the LED leds. You need all the holes clear for the next steps.

Step 4: Snip!

Once all the necessary solder is removed, cut the PCB as shown. Basically this is along the button through-holes just beyond the LED through-holes.

Step 5: Rewire

This picture is of the bottom of the board. There was a bunch of solder here, now we're going to put some back.

Cut a length of wire suitable to your needs (I used about 8" of dual conductor solid speaker wire). Take note of the polarity shown in the picture and solder your leads in.

We had to do several of these, so we settled on the convention that the lead with the white stripe was negative.

Step 6: Power Up

The batteries these come with supply 4.5V, but these things seem to tolerate 5V pretty well. Hook up a power supply to make sure the diode is still working.

They'll draw about 80mA, which unfortunately is more than an Arduino pin can safely handle.

Comments

author
kishabasu (author)2016-06-01

I was confused about the current that the assembly draws. If the diode is rated at 5mW and 5V is applied across it, it should draw 1 mA, not 80 mA, as stated. Could you please clarify how you found the current?

author
vovkulaka (author)2014-05-13

Давно уже занимаюсь подобными переделками дешевых указок. Для удобства и исключения "шортиков" ( трубка с линзой это "-" ) посадите модуль в термоусадку.

temp_-1777889292.jpgtemp_838729664.jpgtemp_1925249827.jpg
author
rimar2000 (author)2014-05-13

Interesting. What things you can do with it?

author
marty_vance (author)rimar20002014-05-13

For the power tool track project I mentioned, we paired them with light dependent resistors to detect when the tools cross the start and finish lines. We use those events to calculate reaction time, speed, and elapsed time.

author
goldust (author)2014-05-13

Hi

Great Tutorial!

you can use another power source for your Laser Diod and use a Relay for switching that via Arduino

Thanks

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