6500K AM transceiver

After the build of the 6500K AM modulator I had to do a compatible receiver. Following the tests with the green LED's I thought they were the right candidates to "antennas"...

before the receiver part build I made a small audio oscillator since it's easier to test with a steady source than a mic, this one oscillates around 1100 Hz.



The oscilator "out" after the pot and 0.22 cap connect's directly to the transmit driver input:

There is nothing simpler, not high performance of course...

Receiving part is just the 2 green LED's connect directly to the input of an LM386 amplifier with 200x gain. Standard from datasheet and no input level pot.

And here the prototype in test:



I got 1 inch range before signal get's to low, in fact signal is just near the noise floor of the LM386, an preamplifier would increase a little bit but using LED's as light receivers isn't the most efficient way of doing things, an LDR or a phototransistor will do a better job for sure. Anyhow it's just a proof of concept....

Have fun!

6500K AM modulator

...Or a "spread spectrum" AM modulator, 390 to 750nm wavelenght, or 400 to 790 THz..... or a white LED AM modulator... now you get it?

Following some LED experiments I wanted to try some light comunication, so decided to do one of the basic forms of modulated light communications, AM, for good or for worst the idea was just to have some fun....

Here's the transmission part, when time permits (I still have a huge backlog on lower frequencies projects) will make some companion receiver and put a mic on this "transmitter".

As you can understand, first I did the schematic and then the final draw on paper...
Any NPN transistor should work but more led's (more power!) will require a more robust transistor, the speaker was just to ear the modulation noise (touching the LM386 input pin), I had no mic at hand.
The pot set's the bias point, and the led should be always on (a steady carrier!?), changing bright by modulation.
LM386 gain was set by an 10uF cap between pin 1 and 8 as standard design.

You can ear noise and see some modulated light in this lousy video:


Have fun!