Trying To Build A Communications Device With A 1-Pound Laser And A 7805

You can get a red laser diode pretty cheap these days—as cheap as £1 in fact. [Beamer] had purchased one himself, but quickly grew bored with just pointing it at the walls. He decided to figure out if he could use it for some kind of communication, and whipped up a circuit to test it out.

To do the job, he designed a modulator circuit that could drive the laser without damaging it. The build is based around the common 7805 regulator and the venerable 555 timer IC. The 555 is set to pulse at a given rate with the usual array of capacitors and resistors. Its output directly drives the input of a 7805 regulator. It’s set up as a constant current source in order to deliver the correct amount of current to run the laser. The receiver is based around a photodiode, which should prove fairly straightforward.

[Beamer]’s still working on the full setup, but plans to use the laser’s pulses to drive a varying analog meter or something similar. Not every communications method has to send digital data, and it’s good to remember that! Video after the break.

28 thoughts on “Trying To Build A Communications Device With A 1-Pound Laser And A 7805

  1. When I read the title, I was thinking it was a weighty HeNe or argon laser – not a £1 laser diode – a HeNe laser would be much harder to blink without additional hardware

          1. Agreed. Just to mess with people’s minds.
            It’s even a reasonable size unit: a K40 laser’s 30 watt output would make it a 17 pound laser. A blue etching laser would be in the range of 2-3 pounds.

            Lord knows it’s a more useful use of the term “pound” than most people on the planet use it for.

            But a (legal) laser pointer is more like 0.0005 pounds, so not so useful. But that would be 250 milligrams.

  2. I saw the title and was wondering what sort of monstrous (1 pound heavy weight) laser this was, then found it was a 1 pound sterling £ (cheap) laser.

    So many different things that use the same names.

  3. “he designed a modulator circuit that could drive the laser without damaging it.”

    Now, THAT’S the trick. My crude experiments in this field have largely been hooking up the laser up to the output of a sound card or a serial port on a laptop with a handful of resistors, then pointing the assembly at a solar cell hooked up to another laptop. Burned up a lot of cat toys before getting things just right.

  4. Eliminate the 7805. Drive an NPN base from the 555 pin3 via 1k and the 3.3V zener to GND. Put a (3.3-0.7)/23m = 100 ohm from the NPN emitter to GND and connect the laser between VIN and the collector.
    The NPN forms a current source, needing only 3 V headroom, so the whole system will operate down to about 6 V.

  5. Using a 7805 as a current-regulating pulse driver. Fascinating. THAT’s a hack!
    When you have a hammer you know, I suppose.

    I wonder what the startup transient looks like on every pulse, and what the real bandwidth is.

    1. ^^this. bounce off a reflective mylar diaphram. when you speak near the diaphram, vibration modulstes the laser. a solar cell driving a high impedance earphone might work for a receiver over short distance.

  6. when you can buy 10 red LASER diodes for £1.57 or less then a £1 LASER seems quite expensive but I digress.

    I’m pretty sure I borrowed the idea from an Elektor summer circuits compilation but I used a 7805 to modulate a LED and another one as a temperature controller for the LED in a piece of test gear so it’s not a new concept to use one as a modulatable constant current driver though it is a neat and cheap hack that works pretty well.

  7. We made a very simple but effective voice-over-laser system back in 2007 using a modulated laser pointer as the transmitter, and a simple solar panel with high impedance headphones as the receiver. We used it to send the audio from London’s Radio Kismet across the room. Details begin at the 19 minute 15 second point in this podcast, with discussion continuing until the 31 minute point:
    Sadly this was the last podcast of my friend Mike KL7R. He was killed in a car accident in Hawaii about ten days later. Mike was the inspiration for this project — he had used a similar system to send computer data across the campus of a university in Alaska.

  8. We did this back in London in 2007. We used a simple laser pointer modulated by a toroidal transformer. The receiver was a small Volkswagen solar panel with headphones across the output. The laser successfully carried the audio from Radio Kismet across the room. I have a link to a podcast in which this project is described in more detail, but it appears that the comment section of HAD dislikes links.

    1. The “trick”, I’ve found to posting links is to first include a line of plain text before copy and pasteing(sp?) the link.

      (If I were to include a link, I would put it here; without the parentheses)

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