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.