Childhood Laser: Building a HeNe Laser Kit

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Introduction: Childhood Laser: Building a HeNe Laser Kit

About: I love building things, from electronics to wood projects. I especially like projects that include LEDs.

This is about building a Class II <1mW Helium-Neon (HeNe) laser. It's also about a dream that's been a long time coming. A little back story would help.

As a kid, back in the 80s and 90s, I used to get Elenco electronic kits from my Dad and Mom as presents. I had them all, the Digital Roulette (K-25), the Space War Gun (K-10), the Pocket Game Dice (K-28) and many more. Even a few robot kits. Then I discovered lasers and all I could talk about for months was getting the brand new Class II Laser Kit (LK-1).

Of course lasers are dangerous and so both my parents said no, responsibly. I continued to pester them and a deal was struck: I write a report on lasers, about their history and safety, and they would buy it for me. So I went to the library, studied up on lasers, wrote the report, and in 1992 I got it. I was so happy I couldn't believe it.

Well, as chance would have it, I lost the instructions and we put off building the kit for a while. Then the whole thing got forgotten and packed away, lost to me for about 15 years. I found it about 5 years ago while I was moving and surprisingly everything was in mint condition. The instructions were still lost and so I checked the internet every year seeing if the schematics would pop up but they never did.

You see the board has no markings and I didn't have a full parts list, only the parts in the box. So the best I could do would be to reverse engineer the circuit, something I'm not great at. A picture would have helped tremendously but I couldn't even find one of those. Finally I tried looking at the Way Back Machine for even the smallest clue but only found this:

http://web.archive.org/web/19970125020504/http://www.elenco.com/dlxkits.htm#lk1

With all hope lost I finally decided to write Elenco for help, hoping that they had the 20 year old plans in their archive. I probably should have tried that first but it never occurred to me. Well wouldn't you know they sent me a PDF of the schematics and instructions the very next day! Suddenly I became a 12 year old again, giddy with excitement. So here I am ready to make a 20 year old dream come true and build that laser kit I begged for as a kid.

So if you're ready then come watch me build this old kit and bring my laser to life!

Step 1: Safety, Tools and More!

This is the step where I tell you to be safe. Lasers are dangerous and if you aren't aware they can cause damage to your vision if used improperly. So please don't look at the laser. You've been warned.

Second, the power supply can be dangerous if you use it without the laser connected. Make sure you are careful with the power, you may get hurt. Or shocked. Anyway, pay attention.

If you're going to make one of these you'll need these tools to begin:
  • Soldering Iron
  • Solder
  • Damp Sponge
  • Safety glasses
  • Needle nose pliers
  • Wire Cutters
If you want to learn more about lasers then I'd check out Wikipedia: http://en.wikipedia.org/wiki/Laser

Attached are the original instructions and a scan of the educational pamphlet I filled out as a kid. Even though Elenco discontinued this kit in the late 90s I still want to point out that this is their kit and their material. I've included it here in good faith and as documentation for others that may find their own kit hiding after 20 years and want to build it:) Don't be a jerk and try to pass it off as your own stuff. That's my disclaimer.

Step 2: Parts List

Below are the parts listed by steps. I tried to lay them all out for reference in the pictures.

Resistors:
  • R1 - 82Ohm 1/2W (gray-red-black-gold)
  • R2 - 1.8KOhm 1/4W (brown-gray-red-gold)
  • R3 - 1KOhm 1/4W (brown-black-red-gold)
  • R4 - 240MOhm 4W (candy striped)
Diodes
  • D1, D2, D3, D4 - Diode 10KV 35MA
  • D5 - 1N4004
Integrated Circuits and Trim Pot
  • 8 pin IC Socket
  • IC1 - 555 IC
  • VR1 - 10K Trim Pot
Capacitors (part 1)
  • C5 - 100 uF Electrolytic
  • C12 - 1 uF Electrolytic
Capacitors (part 2)
  • C1 - 0.0047 uF Mylar (472)
  • C2, C4 - 0.01 uF Mylar (103)
  • C3, C6 - 0.1 uF Mylar (104)
Capacitors (part 3)
  • C7, C8, C9, C10 - 0.01 uF Discap (103)
  • C11 - 0.001 uF Discap (102)
Transformers and Transistors
  • T1, T2 - Transformers
  • Q1 - TIP 30
Wires
  • 9" Black Wire
  • 9" Red Wire
  • 8" Heavy Duty Wire, x2
  • R4 - 130KOhm (brown-orange-yellow-gold)
Laser Tube
  • HeNe Laser Tube
  • Solder Lugs x2 (optional)

Step 3: Resistors

Start this off by connecting the resistors. You may want to measure them with your multimeter before you get started. Two of mine were hard to read because the colors were not distinct enough so this helped me. Here were my results:
  • R1 - 82.5 Ohms
  • R2 - 1.79 KOhms
  • R3 - 0.988 Ohms
  • R4 - Not connected in this step
  • R5 - OL (No reading because it's a huge resistor)
In this step I've also shown how I prepare parts for soldering by bending and placing and how I cut off the ends. This is the practice I'll use for all parts in these instructions.

Step 4: Diodes

The diodes help keep the current running in one direction. This is pretty darn important! These are polarized so you have to put them in correctly or at the least the circuit won't work, at the most you may get smoke. Four of the diodes are the same and one is different.

Step 5: IC and Trim Pot

I added the 8-pin IC socket next and then the trim pot. I did not add the 555 timer chip in at this point. I usually do that last in order to keep the chip safe from heat. Make sure you turn the trim pot completely clockwise, it will help later.

Step 6: Capacitors

The transistors are done in three steps. Start with the two electrolytic capacitors C5 and C12. They have a polarity so putting them in correctly will help. C5 has the positive wire pointing up and C12 has the positive wire pointing down.

The Mylar capacitors are next, C1, C2, C3, C4, C6. They all go on the left side of the board. These are not polarized so put them in any way that pleases you.

The Discap capacitors are last, C7, C8, C9, C10, C11. They all go on the right side of the board. Again, these are not polarized.

Step 7: Transformers and Transistors

The transformers are identical so they can both be placed in the circuit in any order. Solder in the pins on the bottom of the transformers first and then the white wires on the top of the board second. I had to drill out the holes for the white wires so they would fit through.

Then add the transistor. Make sure to attach the heat sink to it first. You don't want the heat sink to touch the exposed transistor wires. Also, don't let the heat sink cover the mounting holes.

Step 8: Wires and Cleanup

To finish up the breadboard you'll want to attach all the wires. Add in the 12V (RED) and GND (BLACK) wires first. Then add in the heavy gauge wire. The left wire is the Negative (-) lead. The right wire is the Positive (+) lead. On the end of the right wire you put resistor R4. After that you're done with the board! Prepare for the laser!

Step 9: Get Out the Laser

This is the fun part. Unwrap the laser. Here's where I found out my laser was a 0.62mW HeNe laser. I knew it was <1mW but this puts it solidly in the Class II range. It's still important to protect your eyes even with this rating, so don't be lax.

The laser is really pretty in my opinion. It has a metal end and a glass end. The metal end is the Negative (-) end and the glass is the Positive (+) end. My laser had a solder lug already on each end of the laser. This made it easy to connect the white wires to it. Make sure the wires aren't all twisted up before you solder it.

I also tried to keep my fingers off the glass. Not sure it makes a difference but I'd rather not take the chance with this laser. I've waited way to long to screw it up!

Step 10: Turn It On!

This was the exciting part for me. First I had to find some power. I really wanted to hook it up to my old Elenco XP-650 deluxe regulated power supply. The circuit should work in the range of 12V - 14V. I cranked it up to 12.11V with my multimeter attached and then hooked up the wires.

Even connected at 12V I didn't get anything, which was expected. I had to turn the trim pot counter-clockwise for the laser to turn on. It flickered and buzzed and then it finally gave me a solid hum and light. My laser worked!

The laser wasn't entirely stable so I turned up the voltage a bit. It worked best for me at 13.5V. That's when it was the most stable.

Step 11: Final Comments

Building this kit was really a dream for me. I can't believe how fun it was to make and what great memories it brought back. I plan to mount this laser soon into a really cool box with some better safety protections. Hopefully that will be another Instructable.

I want to also give credit to Elenco. They have made quality kits for years. They taught me about electronics as a kid and I still love them. I hope you'll give them a shot if you're ever going to teach someone about electronics.

Here's a video of me turning on the laser. I thought it was super exciting and want to share it with you:

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    47 Comments

    A really nice story and a well documented project in case anyone happens to have one of those things knocking around. Even if it's been assembled, this instructable might give clues to how to repair and replace parts.

    1 reply

    That's what I was thinking. This is probably the only documentation of the LK-1 kit on the internet right now. Plus, people probably have variations on this design and this could give them some help too.

    I haven't read the instructable yet, but I just had to commend and say that was a really nice story! Smart parents! :P

    Working on repairing mine, and gonna try not to touch the leads when it is on. Didn't kill me last time tho! :D

    what type of transformers are used?
    i cant seem to find the right ones and none of the shematics show any markings.

    do i need a certain size of laser tube, or can i use any size?

    OK, I read the instructable, and was really pleased to see the details included, Thanks! I've got a box of HeNe tubes and several Hi voltage blocks, all the electronics are encased in epoxy, so as each one quit working, I had no way to repair them. And from this article, I see there's not really that much to one! I can build one, but for a single piece of information I didn't find. What is the voltage input/output of the transformers? (the ratio, I guess is what I'd need to know?)

    Thanks so much for posting this!

    2 replies

    I'm going to have to look into that for you. I'm not quite sure myself. I only have the labels T1 and T2. I'll see if I can't measure it and get back to you. Good luck with your project!

    I would very much appreciate it! Thanks for the reply

    Nice!
    I tinkered with my first HeNe laser tube as a teen in the late 1970's. I still have that tube (it's one like yours but housed in a nice aluminum tube) and another larger one that is 2 feet long.
    Thanks for sharing!
    Every month I looked forward to receiving Popular Electronics, Radio Electronics, the Edmund Scientific, and other electronics catalogs every month!

    2 replies

    Have you ever thought of putting them together again? It would be great to see them work. We definitely need more instructables with lasers.

    I would love to put this back together sometime and share it - time permitting...
    I have been thinking about a revised compact power supply design using a TV fly-back transformer. Thanks to flat-screen technology, there is a glut of surplus CRT fly-back transformers out there for cheap.
    My old power supply was simply a small transformer (120 VAC primary/900VAC secondary) coupled to a half-wave voltage multiplier (like the network of diodes and 0.01µF capacitors on yours) to get the open-circuit output voltage up to the several kV needed to start the tube, and a current limit resistor.

    Great story. I will say though that this is probably out of reach for most. I have used these same tubes for over 30 years in my career field. They are now cost prohibitive as the HeNe tubes are priced over $800. Maybe you can find cheaper but not by much.
    Hang on to way you have and enjoy.

    1 reply

    I noticed that the price has gone up if you buy them new. However I did see some deals on ebay and other sites. Some people have old tubes in good condition and have no idea what they're worth. Might be a good deal for an intrepid engineer.

    I wish you could shoot the laser around the house like that newer James Bond movie.

    1 reply

    My fiancee will wish you'd never given me that idea;)

    What is that red triangular tool? Is that for bending leads?

    1 reply

    Yep. I use it when I want my parts to look nice on the boards I put together. But for most of my life I've just used my fingers to bend leads. You can pick one up for a couple dollars I think.