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