What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Homebrew Wig-Wag Controller Circuit & PCB

DrillBit

Well Known Member
[NOTE: I got a PM from a VAFer interested in building this wig-wag ckt. Pictures in this post having gone to the great bit bucket in the sky, I reposted the pics (consolidated in an attached pdf file) at the end of the thread: see post #17]

I?m on an ultra-slow build plan (kids in college for 6 of the project?s 9 years and counting), so I?ve indulged several low-cost homebrew projects to maintain a glacial pace.

This is an old-school electronic landing/taxi light wig-wag circuit, hacked to the highest standards of Don Lancaster?s ?CMOS Cookbook?. Completely uneconomic making this thing rather than buying, but home-built aviation not being a rational pastime in the first place, what the heck?.

The 1st picture shows the external wiring. Switch inputs J1 and J3, when grounded, each turn on a power MOSFET, providing current to the Taxi and Landing lights, respectively. Just one or both lights can be on at the same time. However, grounding the wig-wag input, J2, always causes the lights to flash alternately regardless of the state of J1 and J3.

WWW.PNG


Connections to the board are all 0.25? Fast-on tabs. Outputs J4 and J5 have on-board automotive blade-type fuses (ATC) protecting the power wires going to the lights. The power line from the bus to J6 should therefore be sized and fused for both lights operating at the same time. There may not much chance of a fault on one of the light?s supply wires that wouldn?t blow the fuse on the input power line, but that?s how I did it. I don?t expect the on-board fuses will blow very often. When was the last time you had a headlight fuse fail in your car? But if I tuck this puppy away behind the panel in a horribly inaccessible position, the fuses will no doubt blow every few days and twice on Sunday.

Optional outputs J8 and J9 are provided for indicator lights on the panel. They tee off the J4 and J5 power lines downstream of their respective fuses, so they will indicate upstream circuit problems or blown fuses. However, they operate normally in case a landing or taxi light burning out, so checking external lights remains a preflight walkaround item.

The board itself (2nd picture, showing just the top copper traces and silk screen for clarity) is 4 x 2.3 in and all through-hole components so ordinary mortals can stuff it and solder the joints by hand. There is room to shrink the layout further, but let?s just say the dimensions cater to pilot-builders with mid-20th century birthdates. Trimpot R1 sets wig-wag timing. At mid-range, wig alternates with wag over a ~2 second period (i.e, 1 second on-time, each side).

WWW2.PNG


All that for about $25 in parts (small qtys) from Digi-Key, and the board was designed with a free s/w package, ?PCB Artist,? from Advanced Circuits. It was a bit more than $25 to turn the design into 5 ?bare bones? prototype boards (just the tinned copper, no solder mask or silk screen). But the durn thing worked just like it did on the breadboard, after reworking a couple of nasty solder bridges. So I went ahead with a full-spec order for 4 boards lest the DAR?some day?recoils in horror at a naked circuit.

The circuit schematic is shown in the 3rd pic. Kind of fuzzy at DR's requested 800 pixels pix width. If anyone is interested in a higher res schematic, BOM, and all that, just let me know. And if any REAL engineers on the forum see something that will cause N478PK to auger in someday, please do comment!

WWW3.PNG
 
Last edited:
Looking for MAX Current your circuit (and DIPs) will handle. Unable to find all the specs for the parts.

I have two 100W lights. With a low bus voltage of 12V, both draw 16 2/3 amps. (8.3333 Amps each) P=I*V or I = P/V, I=16.666667=200/12

Just looking to verify the MAX current your circuit will handle. Is the copper etch on the board capable of handling this much current?
 
Anyone who quotes Don Lancaster is a true veteran of electronics design!
Thanks for sharing and contributing to the open source hardware movement.

I bet you know what a COSMAC Elf and a KIM-1 are, as well.

Cheers,
 
Looking for MAX Current your circuit (and DIPs) will handle. Unable to find all the specs for the parts.

I have two 100W lights. With a low bus voltage of 12V, both draw 16 2/3 amps. (8.3333 Amps each) P=I*V or I = P/V, I=16.666667=200/12

Just looking to verify the MAX current your circuit will handle. Is the copper etch on the board capable of handling this much current?

Looks like the power is handled by the FET's and he has a 10amp fuse inline with the lights.
 
Gary:

Brian's right, all the power goes through the MOSFETs. The ICs are CMOS logic (hex Schmidt trigger and two quad NANDs). The whole board draws < 1 mA when both lights are off.

The board is 1 oz/ft2 Cu and the power traces are 250 mils wide. A 16.7 A current for two 100W lights will flow through a single trace from the +14 V input pin J6 for a length just under 2" long before it splits to feed the two MOSFETs. (Half the current will flow through the rest of traces to each MOSFET, then through the fuses and off-board to the lights, so looking at this part of the power path should suffice.)

According this handy calculator, the temperature rise of the trace will be about 40 C above an ambient of 40 C. So it seems like the board will handle 100W landing and taxi lights just fine, but I have only been able to test it with two 50W halogen bulbs so far--with a power supply that sags to 10.7 V with both lights on. :eek:
 
100 W bulbs

Kurt, Monument Auto in Livermore sells 100 W bulbs, and they are amazingly cheap. I have two in my plane. If you want to try a higher current/voltage source, I can drop off my old Odyssey battery, which is still pretty good.
Leland in P-Town
 
Anyone who quotes Don Lancaster is a true veteran of electronics design!

Thanks for the compliment, Vern, but I'm surely no design veteran. :eek: I only know what a COMSAC Elf and a KIM-1 are because I Googled them just now.
 
Kurt, Monument Auto in Livermore sells 100 W bulbs, and they are amazingly cheap. I have two in my plane. If you want to try a higher current/voltage source, I can drop off my old Odyssey battery, which is still pretty good.
Leland in P-Town

Regarding the battery, sure, why not? I'll send you a PM...thanks, Leland.

I've got plenty of 50W bulbs, so I could hook up two (or more!) in parallel for each side.
 
With Leland's "run-out" battery (didn't charge it up beforehand), numbers for two 50W halogens in series on the taxi light circuit: 7.6 A at 12.2 V = 92.7 W.

The IR4905 MOSFET on-resistance is about 20 mOhm, so it dissapates a little more than 1 Watt at 7.6 A. A calibrated finger on the MOSFET plastic package confirmed temperature just slightly above 37 C (ambient temp about 20 C). With just the one 50W halogen, there is no discernable temp rise.
 
Actually, tried it both series and parallel. Drew about the same amps in both configurations, but the numbers quoted were for parallel.
 
Why not use a solid state four flasher, quite cheap and works very well?
Recreation, education, and finding inexpensive things to do while College Educations soaked up major discretionary Aviation funding (see post #1).

The only advantages this ckt may have over commercial units are negligible currents flowing through the panel switches and the wig-wag action doesn't depend on the loads (one side will still flash if the other is side is burnt out or open circuit for any other reason).
 
Recreation, education, and finding inexpensive things to do while College Educations soaked up major discretionary Aviation funding (see post #1).

The only advantages this ckt may have over commercial units are negligible currents flowing through the panel switches and the wig-wag action doesn't depend on the loads (one side will still flash if the other is side is burnt out or open circuit for any other reason).

In addition to these reasons, I designed and built my own wigwag controller because the automotive-style flasher I initially purchased didn't have a true 50% duty cycle for the lights. One would always be on for a shorter time than the other. Great for cars, but I didn't like it on the plane.

I also wanted to use LEDs and not burn through a bunch of (wasted) power to heat up resistors in order to make the auto flasher work.

Finally, if you open up the auto flasher you'll find a relay inside and associated moving parts to wear out. A Mosfet-powered wigwag controller suffers no such wear.
 
Missing pictures restored in the attached pdf (with reworked text to go with the pdf, page by page...). Click on the thumbnail at the bottom and the pdf should open or be downloaded or something....

Page 1 of the pdf shows the external wiring. Switch inputs J1 and J3, when grounded, each turn on a power MOSFET, providing current to the Taxi and Landing lights, respectively. Just one or both lights can be on at the same time. However, grounding the wig-wag input, J2, always causes the lights to flash alternately regardless of the state of J1 and J3.

I lost the drawing of the 4 x 2.3" board I originally posted. Pages 2 and 3 show the top of and bottom of an unpopulated solder-masked and silk-screened board. Page 4 is a (mostly populated) "bare bones" prototype (no mask or silk screen), showing the input and output 0.25" Faston tabs (J1-J8) along the left and right sides and the blue trimpot R1 which sets wig-wag timing. At mid-range, wig alternates with wag over a ~2 second period (i.e, 1 second on-time, each side). I ran out of Faston sockets for the ATC fuses when I stuffed the pretty green board that's in the plane: so I de-soldered the FS2 and FS4 sockets from the proto board.

I mounted the board on the subpanel with aluminum standoffs at the the four large dia vias in the corners of the board. The vias contact the ground planes on both sides of the board, so those ground planes are connected to the airframe through the standoffs. I bent up an Alclad cover to go over the top of the board (also grounded), in case something tried to fall on and short the topside components one day. However, the cover doesn't completely enclose the board; the ends are basically left wide open to give access to the Faston tabs.

Whether not any of the lights are steady on or completely off, the wig-wag oscillator runs when power is applied to the board, and the sharp edges of the CMOS square waveforms could cause EMI. I generally flip on the wig-wag before engine start and turn it off after shutdown. In flight so far, there's been no hint of noise in the radio or intercom as the wig changes to wag and back again. If I listen very carefully, there seems to be something barely audible coming through after the engine stops until I get the Hobbs and Tach time from the Dynon EMS and open the master contactor.
As always, YMMV.

The circuit schematic is shown in the pdf, page 5. Maybe a little easier to read than the 800 pxl wide picture in the original thread.

View attachment LandTaxiWigWag.pdf
 
Last edited:
Back
Top