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.
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).
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!
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.
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).
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!
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