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

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.

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

Been a busy month - New transmitter, 660nm

It has been a busy month, of building.  Earlier this year I designed a new MCW transmitter using the ATTiny45 microcontroller.
The code has two modes; a beacon mode of three different tones and a solid tone for sending MCW.  I use a hardware interrupt, a switch, to flip between modes.  I used a closed circuit 3.5mm jack for the key.  When it's plugged in the LED is powered off until the key is pressed.  When it's unplugged the power is connected to the LED.

I'll post the code and a schematic of my circuit in a future post.  For now here are some pictures.

This is the inside of the transmitter.  The circuit is built on veroboard, in the center of the picture is the ATTiny45 chip.  Next to pin 5 is the 2N7000 transistor that I use for switching the LED.  Also visible is the voltage regulator, the hardware interrupt switch (red one in the center), and the back of the LED (bottom center).  The transmitter runs off of a 9v battery that fits into a holder in the case.

Here is the top view of the finished transmitter.  If the case looks like a garage door opener, well that's because that is exactly what it is.  I picked it up at AxMan surplus in Minneapolis.  The LED, a Micro Electronics MSB90TA-5, is visible at the bottom of the picture.  It's a 10mm ultra high brightness LED (Radio Shack calls them Jumbo-Super Bright Red LED #276-0086).  It's a pretty cool LED for a test transmitter, has about a 6 degree 1/2 angle, and can run at 200mA with a 10% duty cycle.
I am running it at 50% duty cycle at around 90mA.  It's rated at a luminosity of 10000 mcd at 20mA.   At 90mA (50% duty cycle) the data sheet has it's output at 25000 mcd.  Wikipedia has a good write up on Candela, the measurement of luminous intensity.
In the middle of the case from left to right.  3.5mm key jack, toggle switch for mode selection, on-off switch.

Here is a short video of the transmitter in action.  The transmitter is aimed at my G3XBM receiver. The link will take you to his site and the schematic.  It's a simple design and works extremely well.  I used this receiver, with a couple of modifications, for my initial beacon tests which included some cloud scatter.  Results were very exciting.

Next thing to do is set this up outside and see how far away I can hear it.  I don't plan on putting a lens in front of the LED.  With a 1/2 angle of 6 degrees, it should be good for short range communication.  I'll post my results as soon as my tests are complete.

73,

Warren