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

New Optical System for Receivers and Transmitters

It has been a busy year!

Lots of new discoveries in the optical communication area in 2018 and 2019.  One of the biggest was the creation of a new, modular, mounting system that can be used for receiving as well as transmitting for optical communication.

After building and successfully completing contacts with the 3D printed equipment, I was looking to "build a better mousetrap".
The current 3D printed system worked, now it was time to create a sturdier, light weight, stable platform that could be a more universal system that would accommodate different receivers, transmitter configurations, and lens sizes.

I wanted to avoid the typical wooden boxes that are used to house the Fresnel lenses while still allowing the focal length to be flexible enough to easily adjust in the field.

Many drawings and some samples were built, but none of them covered all of the design criteria.  If it was flexible for multiple configurations, it wasn't stable.  If it was stable, it was a variation of a box and not particularly flexible for different configurations.

I spent about 6 months working this problem out with no real success.  I figured that the wooden box design, which has been used by many optical experimenters for decades, was the way to go.  But then, literally on a rainy November day, while I was measuring out the dimensions for a wooden Fresnel receiver box I remembered my 4x5 large format film camera that I had put in the closet.  I pulled it out and set it up in my work space and stared at for for about an hour until it finally hit me.  A rail system, like my large format camera, would give me all of the adjustments I was looking for.
Sturdy -  check.  Light weight - check. Stable - check.  Configurable for multiple sizes of lenses along with receivers and transmitter configurations - Check!

I thought about taking apart the large format camera and using it's parts to make the assemblies needed, but didn't want to loose the ability of using it in the future.  So I used the basic concepts to design new parts and print them out on my Cetus3D printer.

After many prints of different designs, some successful and others not so much, I finally created a set that I felt worked good enough to share.  So I sent Rob, K0XL, my "partner in crime" well at least in Optical Communication terms, pictures of what I came up with for a new "rail system" for our optical communication experiments.  He thought it was kind of cool, and wanted the files to print out a set of parts to try it out.

This year Rob was also busy this year, but found some time to put together a light system of his own.  His first rig was built from wood with an adjustable receiver mount, but used a "tactical" flashlight he found on EBay for the transmitter.  He switched out the white led and replaced it with a 650nm Red Luxeon.  He modulated it with an ATTiny85 board (a Digispark clone also found on EBay).

He ended up printing a set of my new design, then went on to make modifications.  He created a heftier receiver mount, a different lens mount to match frames that were available to him locally, and crafted a transmitter mount for the flashlight system.

This is a combination of parts which I call the Version 2 receiver.  It uses the K0XL Receiver mount along with my lens mount and tripod mount.

This is a picture of my Receiver mount.  

It also can be used for a transmitter mount.  

It allows for 3-axis adjustments to make sure the sensor or LED is centered in the lens.

The .stl files for the 3-axis mount are at: https://www.thingiverse.com/thing:3751859

The lens mount file is at: https://www.thingiverse.com/thing:3751869

The Tripod mount file is at: http://www.thingiverse.com/thing:3667693

Now a little about my new transmitter design.  If you read earlier postings you'll see that my first design was built using a Digispark ATTiny USB board.  Since that original design I wanted to use the ATTiny series for a PWM modulator.  It took a year of on again, off again designing, but I finally got things working in February this year.  The PWM generation was easy, it was the integration of the audio input into the ADC input to the ATTiny chip that was the issue.  Once that was solved, I just had to put the new system together.

Here is the schematic for the ATTiny25 PWM Modulator

This is the schematic for the new audio amplifier.  It uses a Microchip opamp the MCP6021.  This chip as a DIP or SOIC has a voltage divider built into it and runs on 5 volts.  

More details on the build and testing to come soon.

73,  Warren - WF0T

Schematics for the Mic Amp and the 555 Modulator

I had promised last year that I would publish schematics for the microphone amplifier and the 555 PWM modulator.

I recently spent some time learning how to use ExpressPCB.  Their schematic tool makes a much better picture than my hand drawn schematic I posted last year.

I'll start with the Microphone Amplifier.  I used an LM833 OpAmp in my transmitter, mostly for two reasons; I had a bunch on hand, and I liked the sound it produced.
You can substitute any dual OpAmp (TL082, LF353, TL072, etc.) for the LM833 in this schematic and get good results.

This is a new version of the microphone amplifier for my transmitter from the previous version I posted.  I realized that I didn't need to add the low pass filter to the microphone amplifier.  My optical receiver has a low pass filter in it's amplifier chain, so adding it in the microphone chain seemed redundant.

This is the 555 timer PWM modulator

The LEDs I use are the SFH4550.  These have a 6 degree beamwidth so you can cover a lot of distance without a collimating lens.  My new 3D printed transmitter uses 2 parallel banks of 6 LEDs in series.  I've denoted this on the schematic as D1-Dx for the first 6 and D2-Dy for the second 6 LEDs.  R4 and R5 are valued to limit the current to the LEDs based on the voltage drop of the 6 LEDs and the duty cycle of the timer.

My modulator is set-up to run the LEDs at a duty cycle of 20% so I can run 400mA to the LEDs.  This is roughly 4 times the data sheet value for luminous intensity and light output.  I chose this value to increase the output well past the datasheet value while still providing some life to my portable batteries without having to carry large gel cells with me.

To get to the 20% duty cycle for the LEDs you need to set up the 555 timer to provide an 80% duty cycle. The MOSFET will inverse the duty cycle when switching the LEDs.
R1 and R2 will set the duty cycle of the timer.  I use 12k for R1 and 2.2k for R2.
Keep C3 connections as short and direct as possible.  If you want to add more bypass for the circuit, you could also add a bypass capacitor after the 1N4001 (mislabeled as D1) directly to ground.

I haven't worked up a PCB for these yet.  Currently I am using vero board and I can create a small foot print with those.

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.

10GHz woes...

It's been several months since my last post.  I have been busy!

Been working on my 10GHz set-up.  I am using a Khune Electronics 10GHz transverter with my Elecraft KX3 as the IF rig. 

After operating 2 contests with very little success I started digging into the transverter.
First I found that the receive gain was turned down, turning that up helped immensely.  The transmitter was a different story.  I was using the voltage monitor that is provided and no matter what I tried I couldn't get the output voltage to read higher than 2.9 mV.  According to the manual it should be 1.2 Volts.
I contacted Khune Electronics support and they were extremely response and helpful!  The engineer that responded to my initial questions provided me with my answers and additional test point to investigate to help her trouble shoot my problem.  After verifying the voltages at the test points the diagnosis was not what I was hoping for.  She asked me to return the unit for repair.  Sigh...

Their responsiveness to my questions has been outstanding so far, so I have no doubt that they will fix the issue and return it promptly. 

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.