MUD 2019 - Microwave Update

Here are the various 3D print files that make up my Optical Rail System.

The Receiver mount is made up of three parts; Vertical Slider, Horizontal Slider, and the Tripod mount.

Vertical Slider

Horizontal Slider

Tripod Mount

Thingiverse is the site where I store the files for my Optical Rail System.  Here are the links where you can download the 3-axis receiver mount.

Vertical Slider: https://www.thingiverse.com/thing:3783360

Horizontal Slider: https://www.thingiverse.com/thing:3855590

Tripod Mount: https://www.thingiverse.com/thing:3667693

The lens mount has 2 options.  The first is a 160mm wide mount suitable for frames up to 12 inches.  For longer frames, for holding larger than 12 in square Fresnel lenses, use the 190mm wide mount.

The frames I use are the "build your own frame" kits available at art supply and craft stores.

Lens Bracket with Frame attached with 1/4 inch bolts with lock nuts

160mm & 190mm Lens Bracket: https://www.thingiverse.com/thing:3855639

Connecting hardware for the 3-axis mount is 1/4 inch nuts and bolts, for the lens bracket it is 1/4 inch bolts with lock nuts.

73,

Warren - WF0T

Finally completed the "final" version of a working Light system

The other thing that has been keeping me busy outside of;
working on my 10GHz system, preparing for the Golf Channel AmTour's National championships, playing with my granddaughter and new grandson, and working to pay for all of this,
was fiddling with my light system, namely the housing for the receiver and transmitter.

This is what I came up with.

Front view

Transmitter, on the left, uses 12 SFH4550 IR Led's.  It also uses my 555 timer PWM modulator with an LM833 microphone amplifier.  I eliminated the filtering in the audio amplifier to simplify it as I found that it wasn't necessary.
The receiver is using a 90mm diameter fresnel lens with a 50mm focal point that I found on EBay, I've also seen them on Amazon.  These dimensions are almost perfect for the BPW34 IR detector.  The receiver is the KA7OEI v3.10 on a circuit board designed by K7RJ.
The housing for the transmitter and receiver are designed by me and are 3D printed.  More on that below.

View from behind

As transmitter uses 12 led's wired in 2 parallel sets of 6.  The box contains the circuit boards and the jacks on the back are, from left to right, microphone input, microphone gain, and power.  I've separated power for the mic amp (9V) from the pwm modulator (12V).  I am supplying 425mA to the led's driving them at a 20% duty cycle and I was afraid that I might get noise from the modulator into the amplifier.

First contact was made with Donn, WA2VOI a couple of weeks ago after Tuesday night coffee with the Northern Lights Radio Society at Nokomis Beach Coffee near Lake Nokomis in Minneapolis.
We worked out the narrow beamwidth and then made our contact.  After that we played around a bit bouncing our signals off of parked cars, houses, and piles of snow.  I logged the contact in Log Book of the World.  Just for information, it will take frequencies at lightwaves, I entered it as 3.52e+08 and LOTW resolved it.

3D Printing
I have uploaded my transmitter and receiver designs to Thingiverse.com.  I am making them free to anyone who wants them.
The Transmitter is at: http://www.thingiverse.com/thing:2751923
The Receiver is at: http://www.thingiverse.com/thing:2765972

Each of these prints used less than $1.50 in filament to print.
There are probably improvements that I could make to each of these.  If I develop any into a working example, I will post them here.  If you create any improvements please let me know.

What do Baseball and IR Optical communication have in common?

Seems like a strange question to ask, to start a blog post.
But like they say, a picture is worth a thousand words.

Front view of the IR PWM "Cube" transmitter

So to answer that question...
They share a storage container.
Here is the first iteration of my IR PWM Optical transmitter.  The case is a cube that is used to store a signed baseball.  It measures 3 1/8" per side.  This transmitter uses the same LEDs as my beacon, the Osram SFH4550 IR emitter.  I have them in metal LED holders that I picked up from Radio Shack.

I use a standard 555 timer chip to generate the PWM.  The duty cycle is 22% at a frequency of approximately 70Khz.  Below is the schematic of the transmitter.

555 timer PWM circuit

Pin 5 is used as the input from the audio amplifier.  The audio modulates the duty cycle and not the PWM frequency so my original receiver circuit is able to demodulate the audio. The 555 timer is running in the astable mode.  D1 is a 1N914 switching diode and it's placement between the discharge pin and the trigger pin changes the charging of the capacitor to allow a less than 50% duty cycle.
I wanted a duty cycle of approximately 20% so I could feed 400ma through the LEDs. According to the data sheet that gives a good balance for improved radiant intensity and current draw.

Back of the IR PWM "Cube" transmitter

The back of the transmitter has the jack for the audio source, either a electret microphone or from a laptop sound card for digital modes (upper left).  The knob is connected to a potentiometer that controls the gain of the audio amplifier.  The jack in the lower right is for DC power.  For this version of the transmitter I'm using 6 - AA rechargeable batteries with an output of 7.5 volts.

First version of audio amplifier

This is the schematic of the first version of the audio amplifier that I built.  I liked the way it sounded however I felt that the parts count was too high and the three pole low pass filter was a little over kill, so I simplified it in the final version.

Vero board layout of the PWM and audio circuits

Here is the layout of the boards.  I put the audio amplifier and the PWM/switching circuits on separate boards.  I felt that would give me some isolation of the 70Khz switching noise and the audio amplification.  In testing I haven't noticed any switching artifacts from the transmitter.

I haven't completed any distance testing.  I have bounced the light off of the neighbors garage on one side and the trees in the other neighbors yard, but living in the city the distance is pretty small.
This will be something for another day.

PWM Optical transmitter using a 555 timer

Finally!

After fiddling with the ATtiny based optical transmitter with mixed results for almost 2 months, I put that design on the shelf and pulled out a 555 timer.

I had a solid PWM duty cycle with the ATtiny45.  I could modify it to produce any duty cycle up to 100%.  I had a nice 600Hz tone playing through it with a 20% duty cycle, firing an SFH4550 LED with 400mA of current.  What I couldn't get to work was intelligible audio when adding a microphone and Op-amp.  I got close, but not close enough for me, so I took a break and created this.

555 timer based Optical PWM transmitter

It is a PWM transmitter based on the 555 timer.  The output is fed through a .1uf capacitor to an IRF510 MOSFET, which switches an SFH4550 IR LED.  Power is a 9v battery, so I have a 5watt 18 ohm current limiting resistor which brings the current to just under 400mA.  To be able to feed that much current to the LED I need to have the duty cycle at 20%.  The 555 timer can be used for less than a 50% duty cycle if you put a diode from pin 7 (discharge pin) to pin 2 (trigger pin).  Also R1 needs to be smaller than R2, which is reversed from the traditional timer circuit.  Audio is connected to pin 5 (control pin) through a .1uf capacitor.

The PWM Frequency is about 85 kHz.
These are the values I am using to set the frequency and duty cycle;
R1 = 2200 ohms
R2 = 12000 ohms
C1 = .001uf

For testing I've been using my iPhone to provide audio.  Yes I am using music, but only for the initial tests.  Once I build out the audio amplifier, I will post the completed circuit.  The plan now is to create an amplifier that will be used for an electret microphone as well as a level for a line input from a laptop for digital modes.

Until next time - 73, Warren.

Optical Communications Receiver

Figured it was time to post my receiver.  I mounted it in an enclosure that I ordered from DigiKey.  I thought the side tabs, visible in the photo below, would help in mounting the receiver to the back of my lens box.  #10 bolts fit perfectly.  I've glued two into the lens box and the receiver slips right over them.  I use nuts to tighten the receiver to the back of the lens box.

Here is the G3XBM inspired receiver for Optical Communication.  My previous post contained a link to his site that includes the schematic.  I modified it slightly.  I'm using a BPW34 detector which has a peak response at 850nm (my preferred band).  I also changed the JFET from the MPF102 to the 2N5457.  It has a lower noise figure then the MPF102.  I also switch out the 4.7MegOhm resistor on T2 for a 1Meg resistor.  I did this to reduce the low frequency response to minimize the 60hz QRM from the local street lights.

Circuit board mounted in the enclosure.  Not visible in the picture are the 2N5457 JFET and the BPW34 detector.

Here is the finished receiver in the enclosure.  Behind the little hole in the center is the BPW34 detector connected directly (in the air) to the 2N5457 JFET on the bottom side of the circuit board.
The two jacks on top are from left to right, Power jack and the audio output RCA jack.  This enclosure mounts to the back of the lens box.

I used an RCA jack for the audio to give me some flexibility for connecting to a separate amplifier.  I also can connect earphones or a speaker directly.  So far in my testing, the strobes from passing aircraft are easily heard without any additional amplifier connected.  Aircraft was 10 miles downrange at an altitude of 10,000 feet.
I've also successfully received my beacon using cloud bounce.  Conditions were; overcast sky with clouds at 7000 feet.  Beacon and receiver approximately 500 feet apart with several houses blocking direct line of sight.  Beacon tomes and CW were received at 529 without an external amplifier.
All tests were with the receiver connected to my lens box which uses a 3 1/2 inch glass lens with a focal length of approximately 5 inches.

G3XBM created a super little receiver!  It builds quick, and really works.

Darkness hits early now in Minnesota which is exciting, now there is more time for lightwave experiments.

73,

Warren

First Post

Every Blog needs to have one, so here we go.

Hello, my name is Warren, WF0T, I'm an amateur radio operator.  I have always been fascinated with radio.  There is just something magical about turning a dial and hearing a weak signal from far away.

A little about me - I'm married to a wonderful woman who doesn't quite share my enthusiasm for radio, but certainly doesn't mind me playing.  Her name is Amy, she is a 2 time Ironman Wisconsin Finisher!  We've both ran the Chicago marathon (different years, mine was October 10th, 2010 - 10/10/10) and we were in New York to run the marathon together in 2012 (the hurricane year - that's a blog post in itself) and did run it the following year.  I have two grown children who are amazing, and one super-cute grand daughter.

This blog is a collection of my experiments with optical communication (352 THz) and my recent introduction to the world above 1 GHz.

In March of this year I built an 850nm beacon.  850nm is in the infrared part of the spectrum.  The beacon uses a Digispark USB development board that uses an Atmel ATTiny85 chip.  You program it with the Arduino IDE.  I modified a library that Erik Linder, SM0RVV wrote called Morse and incorporated code from Leah Buechley from the MIT Media Lab who invented the LilyPad Arduino.
The code sends my call and then a series of 11 tones from 23 hz to 4.6 khz, then repeats.

The transmitter/antenna (LEDs) are Osram model SFH4550's.  My beacon has 4, 2 parallel sets of 2 in series and runs for hours on a single 9 volt battery.

Front view and rear view of my beacon.  The front view shows the 4 LEDs in their chrome mounts from Radio Shack.  On the right side near the top of the photo is the DigiSpark and prototyping board.  To the left are the current limiting 4 ohm 1 watt resistors.  The rear view shows the battery connection at the rear of the enclosure.

I presented my beacon at this year's Northern Lights Radio Society, Aurora conference.
www.nlrs.org/home/aurora

I will post my code and the schematic, in case you'd like to try it out, in a future post.

I have several new transmitter ideas on the workbench including a modulated CW transmitter as well as a voice modulator, plus several receivers.

I plan on posting schematics, code, and plenty of pictures from my experiments to excite others to try nanometers and to add to the collection of work on amateur optical communication.