LIGHTING UP A NEW YEAR
For the end of my month mostly-not-off, I finally let myself waste
New Year's Eve and Day on something completely pointless - the
optical communication experiments I didn't get reading in time for
ROOPHLOCH, as mentioned in 2024-10-01ROOflop.txt. As a result this
post will hopefully be transmitted by light before being received
and automatically uploaded to aussies.space. Actually it's being
sent and received by the same computer at the moment, which is
rather pointless, but it makes it easier to debug.
It's all still just a bird's nest of breadboards on my workbench. I
was hoping to start on the cases for the transmitter and receiver
today, but somewhat predictably got bogged down for hours trying to
get the software configuration right. Most things worked quite
easily, but I wasn't getting the EOF character to terminate 'cat'
at the end of the file, whereafter the file gets automatically
uploaded to aussies.space by the receiver computer. The description
in the stty man page really doesn't suggest it, but by trial and
error I eventually discovered that enabling the 'icanon' setting
lets the EOF character (default Ctrl-D) through without messing
other things up.
With that sorted out I experimented with baud rates, and far from
pushing the limits at 200 baud I can get up to 4800 baud over the
short distance of my test rig. Since I'm aiming for sensitivity
rather than bandwidth that's far more than sufficient. So I set to
writing up some transmit and receive scripts to use to post to the
phlog. Even though the stty documentation caught me out, I do think
it's wonderful how short the shell scripts to do this can be:
optictx.sh
------------------------------------------------------------------
#!/bin/sh
# optictx.sh [file] [serial device] [baud rate]
# eg. optictx.sh hello.txt /dev/usb/ttyUSB0 4800
FILE="$1"
DEV="$2"
[ $3 ] && BAUD=$3 || BAUD=200
stty -F $DEV raw icanon -crtscts -echo $BAUD || exit
echo " Transmitting $FILE at $BAUD baud..."
cat "$1" > $DEV
echo -e '\x04' > $DEV
------------------------------------------------------------------
opticrx.sh
------------------------------------------------------------------
#!/bin/sh
# opticrx.sh [filename] [serial device] [baud rate]
# eg. opticrx.sh hello.txt /dev/usb/ttyUSB0 4800
FILE="$1"
DEV="$2"
[ $3 ] && BAUD=$3 || BAUD=200
HOST=ausshell
DEST=/home/freet/goph/phlog
CMD="cd /home/freet/goph/phlog && /home/freet/bin/simplemkphlog.sh"
stty -F $DEV raw icanon -crtscts -echo $BAUD || exit
echo " Receiving $FILE at $BAUD baud..."
cat $DEV > "/tmp/opticrx_$FILE"
echo " Uploading..."
pscp -C -sftp "/tmp/opticrx_$FILE" "$HOST:$DEST/$FILE"
plink -C -batch "$HOST" "$CMD"
echo " Operation Complete"
rm "/tmp/opticrx_$FILE"
------------------------------------------------------------------
A photo of my test set-up, transmitting a pretty modest 47cm
distance from red LED array to photodiode lens, but I'm sure it can
go much further:
gopher://aussies.space/I/~freet/photos/optical_comms/bench_test.jpg
See the 2024-10-01ROOflop.txt for the circuits. I forgot to include
the pull-down resistor on the output to the RS232 TTL adapter from
the receiver board, which I've added there now, but otherwise
nothing's changed.
Soldering up the boards properly should be easy, but the cases are
going to be tricky to work out because they have to fit on top of
my tripods. Maybe I'll get to that on the weekend. Best not put it
off and accidentally let yet another ten months pass me by before
ROOPHLOCH 2025. Still tonight it will be shifted aside yet again to
make way for tomorrow's work, hopefully after successfully sending
this.
In other news, not so much doof-doof music from the festival this
year, it seems. Maybe that style's on its way out? Only those lower
pitch sounds carry this far so it mostly seemed quieter this year.
They had a fireworks display which I went outside to watch but it
was more of a colourful glow at this distance, even through my
wonky highest-magnification binoculars. Just as the display ended
the faint sound of the new year's countdown reached me, delayed by
the distance.
I didn't get around to buying booze for my permitted single day of
alcohol consumption in 2024 (any day, but only once per year),
having finally exhausted stocks. But in a way my apathy there is
exactly the intended result of my rule.
Alright, let's see if this works...
Nope, stty is still confusing me. Adding '-echo'...
- The Free Thinker
