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.
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:
The PC board is mostly thru hole with a couple surface mount
Some day I may do a complete surface mount board, but don't
hold your breath. If you do one, let me know!!
From this site you may download a printable (and readable)
From this site, you may download a printable 1:1 layout of
From this site you may download a PC board file which may be
sent to PC house to order boards.
The board was made using ExpressPCB.com, an online line PC
I used their free software to draw the schematic and to layout
the PC board.
If you want to edit the schematic or the PC layout, you will
have to download the free ExpressPCB software, which is very
easy to use. ExpressPCB free
The PCB layout is such that exactly 2 complete circuits fit on
the ExpressPCB "proto" option boards, which are their least
expensive boards. For about $60 you get 3 boards, each will have
2 circuits, therefore you will get 6 complete optical detector
circuit boards. (about $10 each). Don't hold me to these prices,
this is approximately what I paid in 2008. (Note:
In 2015, the price is approximately the same for a non-silkscreen
board. For an extra charge you can get the "pro" version that has
both a silkscreen and a mask on the board that makes parts location and
This site also has links to a few pictures of the final
stuffed board and a couple of tips on building the circuit.
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.
Schematic in .pdf format You wont
be able to edit this file. If you want to edit the schematic,
you will need to download the Express PCB software and download
the Schematic in PCBexpress format. Use the links below)
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 .DOC format file is a list of all of the specialized
components along with related notes..
BILL OF MATERIAL in word .pdf format
list of all of the components on the PCB. I have included
Digikey part numbers for the less common parts that you may not
have in your junk box.
Here are a few random notes on constructing the PCB
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.
The thermally resettable fuse is a surface mount device. If
you leave it out, be sure to put a jumper in its place.
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:
Mount Q1, the little surface mount transistor, with its gate
sticking up in the air. Connect only the source and drain leads
to the circuit board and have the gate. Be sure to get the D and
S on the right pads!
Straighten the anode lead of the diode so it sticks straight
Solder the cathode lead to the circuit board in the proper
Solder the anode lead directly to the gate of Q1. Adjust
things so the diode is parallel with the board and at the same
height as the gate.
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