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