Antenna tower obstacle light flasher circuit?

ian field

Joined Oct 27, 2012
6,536
I would think that, to avoid having to climb up the tower and replace the bulbs, you would use a longer lasting form of light such as LED bulbs rather than incandescent.

You could control the brightness with a controller such as this with the DC brightness level signal provided by a couple of 555 timers circuits.
Does that sound like something you could put together if the circuit schematic for the timer was provided for you?
I second; don't use filament bulbs for such a safety critical application.

It wouldn't be that difficult to sum in a slow sinewave to the error amplifier of many common types of PWM chip.

A bit of research might dig up an off the shelf LED driver with an identifiable PWM chip. The fed in sinewave periodically makes the PSU think its overvolting - so it dims.

Various options for generating slow sinewaves have been discussed on one of these forums recently.

The slow up/down of sinewave control would be the least harsh on filament bulbs - but I'd still go for LEDs.
 

Thread Starter

Rabbit H

Joined Aug 5, 2016
153
Hmmmm...

Maybe I wasn't clear from the beginning: I'm not against changing the two bulbs to dimmable-LEDs but I don't want to convert to DC, change any of the wiring, or change/modify the fixture's sockets to accept a different style of bulb. I need to maintain the option to quickly convert back to what I have now in case my "flasher mod" suddenly craters some night.

I currently have two 60W LED bulbs (non-dimmable screw-in replacements for common household incandescent bulbs) wired in parallel in an FAA-approved dual-bulb ob light assembly. The two bulbs are currently operated on 115VAC without any modulation. The AC is switched on/off by a photocell. My desire to modulate the bulbs is to make them less of a target for our Texas sniper-wannabees who think that shooting out country stop signs and airport's lights on Saturday nights is manly! (My theory being that it's harder to get a good bead on a light that goes on and off than one that stays on at full brightness.)

My tower services a VFR private airstrip and is well-below the traffic pattern altitude (1000' AGL). Per Federal Aviation Regulations, the tower doesn't require lighting because it doesn't penetrate a prescribed sloping obstacle plane that angles upward from the runway's centerline to traffic pattern altitude. Nonetheless, installing red "ob lights" is an "airporty" thing to do. The only thing the FAA is concerned about is that if I do light it, my ob lights must be red, and not green or blue or mauve or...

Harvey
 
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crutschow

Joined Mar 14, 2008
34,284
Yes, that's basically what I understood from your first thread.
That's why I proposed the AC dimmer circuit with the Velleman kit.
 

Thread Starter

Rabbit H

Joined Aug 5, 2016
153
Yeah, you and I have been on the same page from the beginning but there are a few here (who I'm sure meant well) who don't seem to have a good grasp of how or why I want to modulate my ob lights so I thought I'd take the opportunity to clarify what I'm trying to accomplish.

Harvey
 

Alec_t

Joined Sep 17, 2013
14,280
BTW, the circuit I posted in post #19 was also intended, like Crutschow's, to be used in conjunction with an AC dimmer circuit.
 

ian field

Joined Oct 27, 2012
6,536
Hmmmm...

Maybe I wasn't clear from the beginning: I'm not against changing the two bulbs to dimmable-LEDs but I don't want to convert to DC, change any of the wiring, or change/modify the fixture's sockets to accept a different style of bulb because I want to maintain the option to quickly convert back to what I have now if my "flasher mod" suddenly craters some night.

I currently have two 60W LED bulbs (non-dimmable screw-in replacements for common household incandescent bulbs) wired in parallel in an FAA-approved dual-bulb ob light assembly. The two bulbs are currently operated on 115VAC without any modulation. The AC is switched on/off by a photocell. My desire to modulate the bulbs is to make them less of a target for our Texas sniper-wannabees

LED replacement bulbs can be tricky - some are SMPSU, most are wattles dropper. You probably have to crack one open to tell which.

The SMPSU type probably wont dim well - the one I autopsied had a basic blocking oscillator topology and an unidentified component that I believe is a current sensor. It would most likely try to maintain normal operation down to a low voltage, then just drop out.

The wattless dropper variety can be dimmed with a VFD, as you reduce the AC frequency; The Xc of the capacitor increases and the LEDs dim.

It may still be possible to get dimmable CFLs as a next best thing - a standard wall plate dimmer can be modified so a slow sine generator can control the amplitude.

Presumably; Dimmable LED bulbs can be had - but I've not seen them in any of the shops I visit.
 

Thread Starter

Rabbit H

Joined Aug 5, 2016
153
Mornin' Guys.

Crutschow, if I went with the Velleman dimmer kit that you mentioned (in post #2 of this thread), how would one develop a s-l-o-w sine wave for use as the dimmer's DC brightness control input?

Harvey
 

crutschow

Joined Mar 14, 2008
34,284
Here's a phase-shift, sine-wave oscillator with a clipper on the output that delivers a waveform similar to what you want to feed the Velleman dimmer.

The capacitors are large non-polarized (film or ceramic) capacitors (electrolytics are not suitable) to get the very low frequency oscillation.

upload_2016-8-11_10-19-7.png
 

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crutschow

Joined Mar 14, 2008
34,284
Here's the circuit with an added pot and adjustable shunt reference (acts like a variable zener) that allows adjustment of the clip level.
That might be preferable, to allow for component tolerance variations in the real circuit and the fact that it will likely operate slightly differently than the simulation shows.

upload_2016-8-11_17-15-31.png
 

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Thread Starter

Rabbit H

Joined Aug 5, 2016
153
I ordered the dimmer kit (mentioned in post #2) this morning. Once I get it assembled, I'll start collecting the parts to build Crutschow's sine wave generator (post #34).

Since I'll be assembling the sine wave generator without the aid of a pre-etched pc board, I'm open to advice. I was very involved with military (radar maintenance) and industrial (CNC technician) electronics 30 years ago but not so much since then. Therefore, I'm not up to date on what's available in breadboarding/prototyping nowadays.

Also, once I'm satisfied with a sine wave generator, I'd like to make it a bit more "professional" with a custom etched pc board. (That's just the way I like to do things. I know, it's a sickness! :rolleyes: ) I'm guessing that custom pc boards are easier to produce in small quantities now than they were 30 years ago? Is it still a time-consuming messy process with chemicals that would get me put on an episode of COPS if they were found in my garage? :D

Thanks for all the help so far!

Harvey
 
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crutschow

Joined Mar 14, 2008
34,284
For breadboarding I would just use a Vector type perfboard.

There are companies that offer free layout software and will build a few boards from your layout for a reasonable price, some of which are listed here, such as 4PCB and ExpressPCB.
I think that's preferable over trying to make your own boards, unless you are really into that sort of thing.
 
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