K7RJ's Version of the KA7OEI Version 3 Optical Detector

These pictures depict one way to mount the photodiode and FET.  The board has been laid out so that you could use either a through-hole or surface-mount FET and you may put the FET and photodiode on either the top or the bottom of the board.
Click on an image for a larger version.
                the photodiode for mounting
Preparing the surface mount FET for mounting
Attaching the
                photodiode and transistor to the board
How the FET and
                photodiode should look after final assembly
The completed
                board, ready to go
I made a circuit board for Clint's (KA7OEI), extremely sensitive optical detector.  This page is related to the PC board itself. For detailed circuit analysis and for tons of information about our optical experiments and the genesis of the optical detector circuit, follow the various links in Clint's excellent web pages; Start at: KA7OEI's Optical communication page (link)

Following are important points about this page and the PC board:


Lets get going

The following 5 files are in .PDF format. They will let you view the schematic and various PCB layers without needing the expressPCB software. It should print the layout files at 1:1 scale so if you have your favoriate way to make PC boards at home, you may be able to use these files directly.

The following are PCB layers in printable, 1;1 scale format:

I do not have Gerber files for this PC board as I did not use a program that generates Gerber files. PCBexpress is quck and easy to learn. If you want a gerber file, maybe you could use my basic layout to start from. If you do make a Gerber file, let me know. That would be cool.

The following takes you to the ExpressPCB home page:  expressPCB free software site


The following 2 file are in ExpressPCB format. If you want to edit the schematic, edit the layout or order boards you should run the PCBexpress program then enter these files as required.

The following .DOC format file is a list of all of the specialized components along with related notes..


Here are a few random notes on constructing the PCB

  1. On the schematic: D4 is a protection diode, it in concert with F1, a thermally resettable fuse, provides reverse polarity protection to the circuit if you briefly connect the battery backwards, all too easy to do in the dark. 
  2. The thermally resettable fuse is a surface mount device. If you leave it out, be sure to put a jumper in its place.
  3. The following is important but a little confusing and it relates to mounting the detector diode.  See the following pictures - or look at the pictures to the right to get the idea:

Important Note:  I artworked the board so the diode and FET may be mounted on either side of the PC board. This gives you a little more flexibility on how you mount the board relative to the optics.

Here is how to mount the diode, no matter which side:


Have fun! Our record for over the air light communications using this circuit as the detector, is over 170 miles!

Let us know how you are doing with your optical communications experiments.

Good luck and have fun.

73 de Ron Jones K7RJ


Go back to the "Optical communications" web page - or back to the main Modulated Light page.

This page last updated 20150819

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