Serial Data Transmission Over LASER

This is just a small project I put together that sends serial data from a computer over a laser. It gets received by a photodiode and the voltage is converted into a digital signal which is read by the receiving computer.

Check out my blog site, www.patheticcomputing.com. It's still a work-in-progress but I'd appreciate it if you looked at it. Thanks!

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Closed Caption:

hi i just want to show you guys a small
project that i put together last night
this is a laser communications device it
takes the serial data and it transmits
it over the laser and this is the
receiver end and I know this has been
done before but i just want to give it a
try just for fun and let me show you how
it works
so this is the receiver and the
operation is a pretty simple it just
takes the light from the laser and it
hits this photo diode and then it turns
that into a voltage and its input into
this off amp and the opposite to be a
comparator so the reference voltage is
generated from this trim pot and then
the two values are just compared and
that the lasers hitting this then it
will output a logic high signal and put
it into this ft 232 converter you may
have seen this in some my other videos
and also when the laser hits this light
this LED will turn on and this this
solder spool is here just put as a
weight
alright here's the transmitter end all
it does is takes the serial data and it
puts it into this max 232 clone chip and
convert the rs-232 into a TTL single and
that output signal is put into a mosque
fit which drives the laser on and off
and i also have a lm317 voltage
regulator to supply this laser pointer
with three volts because it used to
double-a batteries i had a lot of
trouble with this part because at first
I had the serial data going straight to
the mosque fit and that's wrong because
the
tto signal on the receiver end needs to
be inverted from the rs-232 single and
then I put a another mosfet in there to
act as a inverter and for some reason
that didn't work either
I maybe I just messed something up but
it wasn't working so I decided to use
this max 232 chip which i spent like two
hours looking for because i couldn't
find it anywhere but i finally found it
and I put it in there and everything
started working alright i dint the
lights so let's see this thing in
operation
all right you can see the green laser
turned on and now let me line up the
photodiode and as you can see the LED
turned on when the laser is hitting the
diode and when it's off it turns off
and now it's on okay i'm going to have
to orient the camera so you can see my
computer screen now
alright so i can't really show the
screen and the laser at the same time so
I'm just going to type some stuff on the
keyboard and you can see the laser is
blinking and i'm only transmitting at
300 baud alright here's the screen
com'on this the transmitter and calm 3
is the receiver i'm just going to type
some stuff in common one and it appears
income three
okay just for fun I have a set-to for
bod or four bits per second it doesn't
work though because the FT 232 chip as a
minimum baud rate but i'm going to type
in a capital you and that is alternating
ones and zeros what's cool is that at
higher bit rates you can see the laser
flicker on that 4800 body right now and
if I hold down a key
you can't see it flicker what's also
cool is that if I modify the laser so
that is off by default and if you
transmit data you can't even see the
laser come on
so that's interesting the maximum
bitrate is 4800 and I've tried 9600 but
the data is corrupted at that point and
that could be for several reasons first
of all you want to use API n photodiode
that has a very short of rise and fall
times but another thing that could
affect it is maybe the MOSFET or the
op-amp doesn't have very good response
times and also the way you connect your
circuit for the photodiode can make a
difference but i have a feeling that
most of it is probably because i'm still
using the driver board for this laser
pointer i just have power going in where
the batteries were so probably something
in there is filtering the signal but it
still works and i haven't done any range
testing it but i'm probably gonna try
that next
anyways that that's it thanks for
watching