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:
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!
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
- Damp Sponge
- Safety glasses
- Needle nose pliers
- Wire Cutters
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
- 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)
- D1, D2, D3, D4 - Diode 10KV 35MA
- D5 - 1N4004
- 8 pin IC Socket
- IC1 - 555 IC
- VR1 - 10K Trim Pot
- C5 - 100 uF Electrolytic
- C12 - 1 uF Electrolytic
- C1 - 0.0047 uF Mylar (472)
- C2, C4 - 0.01 uF Mylar (103)
- C3, C6 - 0.1 uF Mylar (104)
- C7, C8, C9, C10 - 0.01 uF Discap (103)
- C11 - 0.001 uF Discap (102)
- T1, T2 - Transformers
- Q1 - TIP 30
- 9" Black Wire
- 9" Red Wire
- 8" Heavy Duty Wire, x2
- R4 - 130KOhm (brown-orange-yellow-gold)
- HeNe Laser Tube
- Solder Lugs x2 (optional)
Step 3: Resistors
- 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)
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
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: