VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.

  #1  
Old 02-22-2014, 11:10 PM
DrillBit's Avatar
DrillBit DrillBit is offline
 
Join Date: Nov 2007
Location: Pleasanton, CA
Posts: 204
Default Homebrew Wig-Wag Controller Circuit & PCB

[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!

__________________
Kurt Haller
P-town, CA (10 min from KLVK!)
N748PK, RV-9A
Flying as of 13 July 2019

VAF dues last paid 30 Dec 2020

Last edited by DrillBit : 03-20-2021 at 01:55 AM. Reason: Pointer to new post with pictures restored
Reply With Quote
  #2  
Old 02-23-2014, 08:14 AM
RV6_flyer's Avatar
RV6_flyer RV6_flyer is offline
 
Join Date: Jan 2005
Location: NC25
Posts: 3,636
Default

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?
__________________
Gary A. Sobek
NC25 RV-6
Flying
3,400+ hours
Where is N157GS
Building RV-8 S/N: 80012

To most people, the sky is the limit.
To those who love aviation, the sky is home.
Reply With Quote
  #3  
Old 02-23-2014, 08:20 AM
vlittle's Avatar
vlittle vlittle is offline
 
Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,316
Default

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,
__________________
===========
V e r n. ====
=======
RV-9A complete
Harmon Rocket complete
Member of OnSpeed team
The VV in huVVer.tech
Victoria, BC (Summer)
Chandler, Az (Winter)
Reply With Quote
  #4  
Old 02-23-2014, 08:35 AM
Brantel's Avatar
Brantel Brantel is offline
 
Join Date: Mar 2006
Location: Newport, TN
Posts: 7,509
Default

Quote:
Originally Posted by RV6_flyer View Post
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.
__________________
Brantel (Brian Chesteen),
Check out my RV-10 builder's BLOG
RV-10, #41942, N?????, Project Sold
---------------------------------------------------------------------
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
Like EAA Chapter 1494 on Facebook
Reply With Quote
  #5  
Old 02-23-2014, 10:03 AM
az_gila's Avatar
az_gila az_gila is online now
 
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
Thumbs up

Quote:
Originally Posted by Brantel View Post
Looks like the power is handled by the FET's and he has a 10amp fuse inline with the lights.
And no problem on the FETs for current...

http://www.irf.com/product-info/data...ta/irf4905.pdf
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
Reply With Quote
  #6  
Old 02-23-2014, 09:09 PM
DrillBit's Avatar
DrillBit DrillBit is offline
 
Join Date: Nov 2007
Location: Pleasanton, CA
Posts: 204
Default

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.
__________________
Kurt Haller
P-town, CA (10 min from KLVK!)
N748PK, RV-9A
Flying as of 13 July 2019

VAF dues last paid 30 Dec 2020
Reply With Quote
  #7  
Old 02-23-2014, 09:18 PM
Leland's Avatar
Leland Leland is offline
 
Join Date: Jan 2005
Location: Livermore, California
Posts: 146
Default 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
Reply With Quote
  #8  
Old 02-23-2014, 09:35 PM
DrillBit's Avatar
DrillBit DrillBit is offline
 
Join Date: Nov 2007
Location: Pleasanton, CA
Posts: 204
Default

Quote:
Originally Posted by vlittle View Post
Anyone who quotes Don Lancaster is a true veteran of electronics design!
Thanks for the compliment, Vern, but I'm surely no design veteran. I only know what a COMSAC Elf and a KIM-1 are because I Googled them just now.
__________________
Kurt Haller
P-town, CA (10 min from KLVK!)
N748PK, RV-9A
Flying as of 13 July 2019

VAF dues last paid 30 Dec 2020
Reply With Quote
  #9  
Old 02-23-2014, 09:48 PM
DrillBit's Avatar
DrillBit DrillBit is offline
 
Join Date: Nov 2007
Location: Pleasanton, CA
Posts: 204
Default

Quote:
Originally Posted by Leland View Post
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.
__________________
Kurt Haller
P-town, CA (10 min from KLVK!)
N748PK, RV-9A
Flying as of 13 July 2019

VAF dues last paid 30 Dec 2020
Reply With Quote
  #10  
Old 03-03-2014, 09:24 PM
DrillBit's Avatar
DrillBit DrillBit is offline
 
Join Date: Nov 2007
Location: Pleasanton, CA
Posts: 204
Default

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.
__________________
Kurt Haller
P-town, CA (10 min from KLVK!)
N748PK, RV-9A
Flying as of 13 July 2019

VAF dues last paid 30 Dec 2020
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 06:26 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.