| Author | Message | ||
     Chris |
Greetings, I love this site!!! Your stuff is awesome!! Anyhoo.. I'm building a laser communicator and would like to hook it to my computer power supply using the 5V rail on a 4 pin molex plug, and I'm not sure if 5V is going to overload my laser or not?? If not, would I get a better signal in doing this?? On a side note, would a green, argon based laser work for this experiment/toy?? (like the green laser pens). Thank you for you time. | ||
| Simon Quellen Field (Sfield) |
Ohm's Law will tell you how to run your laser using a higher voltage. First, measure the current the laser is using with the batteries supplied with it. You do this by connecting a millammeter in series with the batteries, and turning the laser on. Let's suppose the laser is using 3 volts at 50 milliamps. Measure your new power supply voltage (to make sure it is what you think it is). Suppose it is a regulated 5 volts. Now you need to limit the current in the laser to 50 milliamps. Here's where Ohm's Law comes in. The resistance you need is the voltage divided by the current. So, 5 volts divided by 0.050 amps is 100 ohms. So, if you place a 100 ohm resistor in series with the laser, the current will not exceed 50 milliamps, and your laser should be safe. It is excess current that destroys them. Green laser pens are not argon lasers. They are infrared semiconductor lasers shining through a special material that doubles the frequency of the light (very inefficiently). You would get much better range using the infrared laser by itself (although it is now a little more difficult to aim, since you need a video camera or digital camera viewfinder to see the dot). That said, the infrared semiconductor laser can be modulated the same way as the red laser can. More current will be going through the transformer (since the infrared laser is much more powerful, to make up for the inefficiency of the frequency doubling crystal). It may run warm to the touch. | ||
| Chris |
Thank you, you have been most helpful (mental note, kick guy at staples that said it was an argon laser, grrr) Now, off to build my laser.  | ||
| Dan |
I have about zero knowledge of electronics, but in the original post, does increasing the voltage and limiting the current increase the power output of the laser or does it remain the same? | ||
| Simon Quellen Field (Sfield) |
The power of the laser is set by the current. All we are doing with the resistor is keeping the current the same, while we change the voltage. Thus, the power of the laser will stay the same. Putting more current into the laser will destroy it. Semiconductor lasers operate on the edge of destruction. To get them to lase, the current is brought to just below the amount needed to destroy the tiny little crystal. | ||
| Dan Tolle |
I see, Than kyou very much. | ||
| mahbub rasul |
Hello Mr. Field, First I want to thank you about your wonderful website. It's really cool. I am trying to make the laser communicator for my science project. I am in thought that whether a normal laser pointer will be able to concentrate on the solar cell in broad daylight. It would be great to have your advice. | ||
| Simon Quellen Field (Sfield) |
Just put the solar cell at the far end of a tube, such as a pipe or the cardboard center of a paper towel roll. This will shield it from daylight, and the laser can still point down into the tube to hit the solar cell. | ||
| Robert charmanzer |
i think laser pointers are banned in Australia, cus in an aeroplane, the shone the laser into the cocpit and they thought it was a sniper and cus it can blind you. so the nly way i can get one is from your site, is it more money to post it to Australia? | ||
| Anonymous |
laser aren't banned in Aus i a pack of 5 just last week from a toy store | ||
| Jai Kapadia Unregistered guest |
hello i am trying to make the laser communicator for my phy project.please tell why is the transformer used?can can it be made without a transformer or can i directly connect it to audio output of my stereo without extra battery?can any transformer other than 8 ohm to 1000ohm be used | ||
| Simon Quellen Field (sfield) New member Username: sfield Post Number: 22 Registered: 12-2004 |
The transformer is the modulator. It is how the signal from the stereo is mixed with the signal from the battery. Without it, the battery would be directly connected to the stereo, and the stereo's output transistors would be damaged. The transformer acts like a lever, converting the power level from something that pushes hard for a short distance, into something that pushes gently for a longer distance. It matches the output of the stereo to the input of the transmitter. Using a different transformer would be like using the wrong gear in a car -- the output would not be most efficiently coupled to the task at hand. | ||
| Jai Kapadia Unregistered guest |
can u explain with more details how the transformer modulates the input signals?can i directly connect the laser to my stereo without using battries and transformer(just laser directly connected to speaker output of stereo? | ||
| Simon Quellen Field (sfield) New member Username: sfield Post Number: 24 Registered: 12-2004 |
You want power to go to the laser that is very close to what the batteries normally produce. Too little, and the laser won't operate. Too much, and the laser is destroyed. An audio signal goes from -peak to zero to peak. You want a signal that goes from about 4.495 volts to 4.5 volts. The transformer keeps the DC level from the batteries, and allows the stereo to wiggle the voltage level a little bit. The transformer injects just the right amount of wiggle, without letting any DC from the battery get back to the stereo. | ||
| John Ragland (Unregistered Guest) Unregistered guest Posted From: 64.12.116.130 |
Hello Mr. Field, My son had great success two years ago with the simple laser communicator and he is trying to do the project again this year with some modification. He wants to add a green laser module along with the red laser so that he can have 2 audio sources going at the same time. The lasers will go through a single beamsplitter through optical filters to two separate receivers. That way at each receiver, by using the filters, you can select which audio source you want.The circuit works perfectly with the red laser in the circuit, but once the green laser module is tried in the same circuit,the laser module does not come on. The same laser works perfectly when connected to just a 3 volt dc source. I am assuming that there is an impedance mismatch between the transformer and the green laser module. I have had difficulty finding the input impedance for the green laser. If you have any information or suggestion regarding this, I would greatly appreciate your expertise. If you think it may not be an impedance mismatch, any suggestions would be appreciated. P.S. I have noticed that some people are having problems burning out their red laser. We had the same problem, and found out that it was the stereo wires we used to hook up the system. Stereo wires will short out the laser and burn it up quickly. Mono wires did not burn out the red laser. Thank you, John | ||
| Simon Quellen Field (Sfield) Senior Member Username: Sfield Post Number: 847 Registered: 12-2004 |
The lasers that burn out have no internal circuitry to keep the current stable, not even a simple resistor. They rely on the internal resistance of the three button cells, and cannot handle the current spikes when larger batteries are used. To prevent that, place a bi-color LED across the 1,000 ohm side of the transformer. Any current spikes will go through the LED, causing it to flash. The LED can safely absorb much more current than the laser can, and because it is bi-color, it will absorb both negative and positive spikes. Use only the two-legged form of the bi-color LED. Green lasers are actually high power infrared lasers, shining through a frequency doubling crystal. Only a small portion of the infrared laser light is transformed into visible green light. This means that the infrared laser needs as much as 100 times the current that the red laser does, to produce the green beam. Measure the current the green laser uses by putting an ammeter in series with the battery. Then measure the current when the transformer is also in series with the battery. The current will be lower, and is probably not high enough to make the laser operate. Since the green laser is much more expensive than the red ones, it would be a very good idea to make sure the transformer has the bi-color LED attached to absorb current spikes that might damage the green laser. You can bring the current back up to the required amount by raising the voltage. Do this a little at a time, watching the ammeter while you add an extra battery. Be aware that you may destroy the green laser if the current exceeds the original measured amount. | ||
| mnado (Mnado) Senior Member Username: Mnado Post Number: 178 Registered: 12-2005 |
If your going to use USB for the connection what pins should be used? There are 4 of them. I just don't want to keep on moving the CPU just to connect the serial port connector. How much voltage does USB's produce? do is still need a battery to connect at the laser? I didn't used a battery to the laser com at the serial port, because it produced enough voltage and amps to light the laser, and reach my friend's house. | ||
| Simon Quellen Field (Sfield) Senior Member Username: Sfield Post Number: 1072 Registered: 12-2004 |
Use a USB to Serial converter, not just the USB by itself. | ||
| Louis Edelman (Computerleet) New member Username: Computerleet Post Number: 2 Registered: 2-2008 |
What transistor would you have to use if you were doing it with a USB cable. I assume you would use the white and green wires and hook them up to the same configuration but i don't think you would still use an audio transistor. | ||
| Louis Edelman (Computerleet) New member Username: Computerleet Post Number: 3 Registered: 2-2008 |
So you use an NPN transistor why cant you just use the White and Green data wires in the circuit. For the project i want to do i want to connect my digital camera to my computer via the laser. | ||
| Theresa Simmons (Theresa) Member Username: Theresa Post Number: 15 Registered: 1-2008 |
How do you plan to teach your digital camera to send the data in Morse code? Do you know how long that would take to send, anyway? Morse sent at 20 words per minute is 100 bytes per minute. A typical JPEG image of 3 megabytes would take three weeks to send: "http://www.google.com/search?q=3+megabytes+%2f+%28100+bytes+per+minute%29" |
