Visual Beacon on PCB
A Construction Article
This is a reprint of an article from 3 months ago with the addition of a layout I did of the design. The pics are revised to show the PCB version. The board size is the same as the proto and looks a bit cleaner as you might expect.
I was chatting with an RC friend the other day and we started talking about how hard it is sometimes to see things especially when they get to the edge of our visual field. He happens to be an FPV pilot. So, as engineers, we always try to solve the problem.
One suggestion was to put a beacon on the aircraft, sort of like those very strong blinking lights you see for bicycles. Of course, you could buy one of those and take it apart, but that’s no fun. So, we decided to build one. We had both seen some of the very powerful LEDs at Anchor Electronics, 0.5watt, which seemed to be the solution. We agreed on a basic design, then each of us did some tweaks; pretty much the same result, but each path was a bit different. This article shows how to build the Tim version.
Below is a pic of the finished board with a pass thru deans connector. You can see from the size of the deans the relative size of the beacon.
Full up Beacon, Prototype
Prototype Beacon Board
Above is a closeup of the board, it’s 1.4” x 0.75”.
Final Beacon on PCB
Below is a pic of the relative layout to make the hookup easy if you use a proto board. The PCB version is close.
Part Placement and Board Size
Below is the schematic which uses a classic 555 timer and a dual FET to drive the LEDs. The LEDs are driven at about a 25% duty cycle and about 2x power rating, so overall at 50% their rated power. I used mostly surface mount components to make the board size small. The board size could be further reduced by using a surface mount 555 and putting parts on both sides of the PCB.
Schematic for Beacon
I was at Anchor this week and now they have a 1w version of the LEDs which is 2x the rating of what I used here; using the 1w version would require better drive circuitry to leverage. Maybe a project for another day.
I did a layout on this design using eagle cad, bare board pic shown below. My son turned me onto a company named OSH Park which uses the native eagle board file to produce inexpensive boards with easy processing.
The printed circuit boards were relatively inexpensive, the above 3 boards cost a total of $5.40 shipped with 2 week delivery. The general price for double sided 0.062” boards is $5/sq in. This board is 1.05 sq in and you get 3 boards for the above price. A nice deal.
I was really impressed with OSHPark as a supplier. I uploaded the bare blinky.brd file (native eagle cad file, project blinky) without generating gerber files (board artwork). They did the processing online and rendered the board as I waited so I could see what I was getting. I used eagle 7.0 freeware for this one, but there is a 7.1 version available now.
Once ordered using PayPal, the 3 boards were then put on a larger proto board with other designs and fabricated. They emailed me when the board filled up and went to fab and again when they shipped the boards. This company is in Oregon, so ship was pretty quick. Of course, status is always available via their website.
If anyone is interested, I’m willing to provide the board file in eagle cad, just drop me a line. I’ll try to find a spot on the website to put the file.
Further details and some alternatives
1. You could change the 555 type and drive the LEDs directly from a bipolar 555. The CMOS version used here cannot deal with this level of current. The bipolar 555 (older) can source ~200ma which is pretty high but even with a single LED the brightness would be less than this design.
2. You could use a dual p channel FET and alleviate the2N3906 transistor.
3. The CMOS 7555 was used because it’s rated for 15v abs max and let me get above pinch off on the FETS (~4v) easily for a simple design. So, this version is restricted to a 3S battery usage.
4. The design could be adapted to run on different batts, but would require more circuitry. For 1S and 2S, would need to boost voltage for the 555 because of FET pinchoff. For 4S, would need to buck down voltage for the 555. FETs are rated 50v so they are ok, and LED current limit resistors would need to change value.
5. On the packaging side, could reduce PCB area by converting the 555 to surface mount and putting parts on both sides of the board.
Attached to the website version of this article is a zip file (using 7zip, .7z) that contains the .brd and sch files. You can use the .brd file to order boards directly from OSH Park.
So, if you’re looking for a short and interesting little project, you might build a beacon.