The picture above shows how mine looks but you can make the design of yours look totally different if you want to.
It's going to become a burning laser with controllable current. (current-regulated with an LM317T).
You can choose between a 9V battery and an external power input (see first picture on the left side).
Other regulators then an LM317T are also possible to use here. If you have any questions about them, ask it here!
It might be fun to have a burning laser, but not when it burns that one thing you don't want it to burn.
Use safety glasses! This is really not a simple toy.
High power lasers might also not be allowed in your country, keep that in mind.
I am not responsible for any accidents with this device, however all dangers are well noted in this instructable.
A video of the laser in action:
A video of the laser in action with a spirograph:
Step 1: Requirements
(* means Required)
- Hot glue or other glue.
* A soldering iron /w soldering wire.
* A laser diode.
* A 100ohm potentiometer. (250mW)
* A 3.3ohm resistor (or 3x 10ohm resistor in parallel). (3x 250mW or 1x 0.5W).
- A regular diode 1N4001-1N4007 (everything between is also good).
(or any other diode that can hold a reverse voltage of at least 40V)
- An On-Off switch/push-button/... as a main switch for the circuit.
- An On-On switch for switching between battery or external input.
* A 9V battery clip. (click here if you don't have one)
- A 9V battery. (not required if you use the external power input)
* An LM317T regulator (really cheap).
- An enclosure/box to put the whole project in -> I used an 8*5*3cm = 3.15*1.97*1.18inches black project box.
* A lens for adjusting the focal point of the laser beam.
- A connector for the external power input (if you want to use that).
* PDF reader for the datasheets.
* Your healthy brain and attention for safety measurements.
Step 2: The schematic
It doesn't use a capacitor for flattening the output voltage of the LM317T because the output signal is already perfect.
It's also dangerous to use because when you remove the diode, the capacitor will charge to higher voltages as allowed for the diode, and when you attach it again your diode will be destroyed.
We also don't use an inverse parallel diode because that's not required. Your LM317T can't give negative voltages. Even if it did, the laser diode is a diode which means it can take negative voltages (-2V).
And even if your LM317T would somehow create negative voltages, your diode would die anyway because it means the regulator is broken; no current regulation means dead diode. I don't see why people put diodes over there.
You can use a 9V battery or an external power input for this laser burner (choose between both with S1).
When using the battery, all is ok, but when you use the external input you should keep this in mind:
If your diode works at around 4V and your voltage source is 9V then the LM will have to dissipate the remaining 3.75V by converting it into heat.
Dissipating 5V is allright.
The LM is made to handle a maximum voltage of 40VDC. If you would do that, and your diode still works around 4V then your LM will have to convert the remaining 34.75V into heat. This is possible - with an epic heatsink - but we want to keep things compact right?
If you use a small heatsink and 40V input, then I ensure you your LM will be fried. (maximum junction temperature for the LM317T is 150°C, 302°F)
If you want to have an extra trim potentiometer for inside the casing, I suggest using a 50ohm potentiometer - 250mW.
D1 will be protecting our circuit from inverted polarity.
D2 is the laser diode.
R1 will protect R2 from being toasted (current limiter).
R2 is the potentiometer which will control the current trough D2.
Iadj is the adjustment current from the LM317T (see datasheet ).
Step 3: What will the LM317T do?
- If the resistance of the diode decreases, and the voltage over it would stay the same you'd expect the current to raise, but the LM317T will then lower the output voltage so that the current stays constant.
- Same when the resistance incrases
- If the input voltage changes (increases or decreases) the LM will make sure the output voltage doesn't change.
Example: Switching from battery to external input or having a flat battery
Notes: The output voltage can never be higher then the input voltage, so if your battery goes lower then 4V then the LM won't be able to keep a constant voltage at the output.
Other regulators like a 7805 are also possible to use here. If you have any questions about them, ask it here!
Step 4: Some calculations
What input voltage do we need (first picture)?
At the amperage we're working with, the regulator needs a voltage differential of at least 3.5V between the Input and output pins. (graphic 1)
Supply voltage must at least be: 4V (diode voltage) + 1.25V (reference voltage of the LM317T) + 3.5V (minimum voltage between in and output pins, = Vdc)
-> this is why we use a 9V battery, and not some AA batteries.
This is roughly calculated at the maximum ratings.
What happens when we go below that voltage? (when battery dies)
As soon as we go below 8.75V the intensity of the diode will decrease, but our LM317 will still work untill the voltage drops below 1.2V (defined in the datasheet , however I don't understand why because it needs at least 1.25V between the 2 pins ).
What happens when we go above that voltage?
See step 2 (40V)
Power dissipation in, and current trough the two resistors (second picture):
As you can see in the graphic, the maximum current will be 378.8mA. That's when our potentiometer is set at 0ohm.
The maximum power dissipation in the 3.3ohm resistor will be 473.5mW. This is why we use a resistor rated 0.5W (or 3 0.25W resistors).
The maximum power dissipation in the 100ohm potentiometer will be 118.4mW. This happens at the moment when the resistance of the potentiometer is 3.3ohm, which is the same as our protection resistor.
When the resistance of the potmeter drops below 3.3ohms, the power dissipated there will also drop because the voltage over the potmeter drops. (P = U*I)
The power in the 3.3ohm resistor will keep rising until 473.5mW because the voltage over it, and current trough it will also keep rising.
As you can also see in the picture, the current will start rising from the moment we reach 20ohms and lower.
From 20ohms and higher, the current doesn't change a lot any more. You will notice this effect when testing your laser: The laser will shine just a little until you reach the point of 20ohms or less, and then suddenly you'll think "oh, so my potentiometer Does work".
I would like to use another potentiometer (47ohm or 50ohm) but I can't find them anywhere. We'll have to do with the 100ohm pot.
Another solution for this problem is to use a double potentiometer (2 of them, on one axis) and put them in parallel. You'll then have a linear 50ohm potentiometer.
(I didn't have enough room for that now on my print-board, so I can't do that).
What to do when you've gathered an EPIC diode:
High power diodes will probably work at higher voltages then 4V.
You should look up the datasheet of the diode you have, and use this formula again to calculate the minimum power source voltage:
Vsource = DIODE_VOLTAGE + 1.25V + 3.5V
This is a reference datasheet if you can't find any: click!
Output current calculation:
The output current can be calculated with this simple formula:
Iout = (Vref / (R1+R2) ) + Iadj
Iout = 1.25V / (R1+R2) <- formula for your potentiometer
(where R1 is the safety-resistor and R2 is the potentiometer)
(because Iadj is several microamps, and Vref is 1.25V)
(Iadj is indicated on the schematic, see datasheet for explanation)
Because the regulator will keep the voltage between pins OUT and ADJ at exactly 1.25V
(1.2V to 1.3V, depending on the junction temperature)
It's very logical how the current regulation works, it's just ohm's law. The whole regulation is all about the regulator trying to keep that voltage at exactly 1.25V
Potentiometer at lowest resistance:
Iout = 1.25V / (3.3ohm + 0ohm) = 378.8mA
-> current is now at it's maximum.
-> Theoreticly we can have a diode of 380mA * -+ 4V = 1500mW
If you would like to have a diode with larger power, you'd have to choose lower safety resistor with higher wattage.
You can ask me to make some new calculations and graphic of this in the comments below.
Potentiometer at highest resistance :
Iout = 1.25V / (3.3ohm + 100ohm) = 12.1mA
-> current is now at it's minimum.
Potentiometer at lowest resistance, without protection resistor R1:
Iout = 1.25V / (0ohm + 0ohm) = infinite mA (theoretically)
-> your diode is now fried.
(the current will depend on the maximum current and voltage your supply can deliver and the resistance of the diode, so it won't be infinite but your diode will be anyway).
Step 5: Heatsinks
However! That doesn't mean you don't need a heatsink.
I'm not going to calculate the size of it because even the smallest heatsink existing on earth is enough for the regulator :)
(using NO heatsink is possible, but you have to Really know what you're doing with the input voltage. Even I added a heatsink for if the input voltage would accidently be too high. I'll save my circuit from being fried for a few moments so that I have time to interact)
If you Don't have a power source with a fitting voltage, you'll need to have a larger heatsink, but I suggest you just try some different heatsinks untill you found a good one.
Ok, so far for the LM heatsink.
The diode needs a heatsink too!
This little guy will create most of the heat in the whole circuit, so this is the one who actually needs a good heatsink.
do not overreact like on the pictures I find on google (like this one or this one )
The heatsink I took for my diode is also too large because it never gets warm. I just took it because it was the only one I had (See picture above)
Step 6: Where to get your diode
Different types of diodes:
Low power IR diodes are found in CD readers.
High power IR diodes are found in CD burners (CD/RW).
Low power red diodes are found in DVD readers.
High power red diodes are found in DVD burners.
Low power violet (blu-ray) diodes are found in blu-ray readers and HD DVD players.
High power violet (blu-ray) diodes are foind in blu-ray burners and HD DVD burners.
For example, I will be extracting a laser diode from a DVD burner. Take a look at all the pictures above here to see how to do it. Instructions are added with the yellow tags.
Note: Red DVD burner diodes are mostly used for laser burners because they are the best diodes that you can find most easely.
Don't expect to find a blu-ray burner diode somewhere
IR (infra-red) diodes are just as dangerous as other diodes, but the difference is that you can't see the danger!
It would be really stupid to think that when you see just a little light, that it can't burn your eyes!
Again: Wear protective glasses!
Step 7: Diode assembly
Because the diode fits in there tightly, the heat exchange will go really easily, and since these things are round, so we can just drill a hole in our heatsink and push this in.
Picture 2,3 and 4 show which pins have to be connected. Soldering might be hard when the pins are really short. When you solder, make sure the diode doesn't get too hot! Solder quickly.
You can now use the connector from picture 5 to connect the positive pin from the diode to your circuit.
If you've connected your negative wire to the heatsink, you don't need to connect a wire to the negative side of the diode.
That pin is the same as the case.
Step 8: Assembling everything
First make a small hole with anything, and then make the hole larger by rotating your scissors in there.
This way you can have all sizes for you hole you want to.
You'll have to make a big hole for the potentiometer, a small one for the push-button, and another small one for the switch.
Then a hole for your laser diode and maybe some holes for your external power connector.
Assemble everything, and don't forget to leave some room for your battery!
You can use a plastic piece like I did, for fixing the battery in place. (glue in the box with hot-glue or super-glue).
For all other components, you don't really need a print-board. You can just solder them together in the plastic box. (like I just soldered the diode to my push-button).
Step 9: Trying out your diode for the first time - tuning the diode current
Believe me, the chance is really high you'll just kill your diode if you have no experience with laser diodes.
- Make sure power is disconnected.
- Place the diode inside the heatsink and not outside because it will probably get broken from overheating.
- Make the connections from the circuit to the diode.
- Wonder why, but accept that you don't need a lens yet.
- Turn the potentiometer to the Highest resistance.
- Turn on the power.
- SLOWLY decrease the resistance of the potentiometer by rotating it.
- The diode will slowly start shining brighter.
- Suddenly it'll go shining brighter really fast when you just turn a little.
- This is the moment when you really don't want to go too far.
- If you don't want to risk killing the diode, stop here.
- Rotate a little further -really carefully - until the brightness stops increasing. Stop there! don't go any further.
- When light intensity starts decreasing a little, go Back immediately, but not too much, just a little until it goes back to the highest brightness. (it means you went a little too far, but if you turned very slowly, you probably didn't damage the diode).
Another, more precise method is to look at the line pattern of light (see pictures of the red diode above) that your diode emits.
Usually, the pattern shouldn't change when you increase the current trough the diode.
When you suddenly see it starts to deform, that's the moment that -if you go a little further - your diode is broken. Like in the other method, go back a little as soon as you see the pattern is deforming. It'll be perfectly adjusted.
This second method doesn't work on all laser diodes because not all of them show line patterns like this.
Step 10: Creating a focussing system
I had a little thought about how I could create a simple thing to adjust the focal length of the beam.
I came up with this great idea to use a broken potentiometer, Recycling ^^!
So you need a potentiometer, two screw nuts, or at least one (it's probably already screwed on the potentiometer) and a nipper.
- Take the potentiometer apart with the nipper.
- Don't damage the screw-thread.
- Break off the remaining metal, leave only the piece with the thread.
- Take your lens and glue it on the piece with the thread.
- When using super-glue, make sure the glue fumes don't corrode the lens. You risk colouring the lens blurry-white!
-> solution is to keep blowing on the lens to lead away the fumes.
- Make sure you glue the lens perfectly in the middle because else the laser dot will rotate when you adjust the focal length.
- Screw the nut till the middle of the thread.
- Hold the lens in front of your, turned on, laser diode.
- Measure the distance from the nut till your project box at the moment the beam is focussed as small as possible at a large distance.
- Find a short tube that just fits around the thread without tension. -> A plastic pen is good for this.
- Cut the tube to the measured length, and make sure it's perpendicular.
- Glue the nut on to the tube.
- glue the tube on to your box, exactly in the middle of your laser diode
Now what's the use of that second nut?
The second nut is for fixing the lens in place. If you would only have one nut, the thread will start moving when you pick up your laser.
Step 11: Any questions?
Also: No, this laser doesn't make a super bright line of laser light, but that's because I don't take pictures in a bathroom full of vapour.
If anything is not clear to you, don't hesitate to ask it here!
All questions are welcome, I'll try to answer them as fast as possible.
If you like this tutorial, please comment!
Oh, and if you think something in this tutorial is still missing, also just tell me here ;)
Have fun and be safe!