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Old Jan 21, 2015, 02:08 AM
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Question
PWM controller on/off electronic switch

I recently bought a headlight "system" from HobbyKing and it came with a small PWM controlled switch to be able to switch the lights with a channel.

The switch was a simple combination of a pwm decoder and transistor and it would be possible to put one together oneself, but at the cost of size and weight of course.

I'm looking for somewhere to buy this kind of device online. Google and the ebay searches hasn't helped me much so far. Anyone know where I can get a device like this?
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Old Jan 21, 2015, 02:54 AM
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I'm guessing by "PWM" you mean a switch controlled by the PPM (or servo) signal from an RC receiver. Google or EBay search for "receiver controlled switch" or even "RC switch" and you'll find loads of them.

Steve
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Old Jan 21, 2015, 03:09 AM
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Slipstick, you got PWM and PPM mixed up. I also don't see much for RC switches on ebay. At least not for a reasonable price.
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Old Jan 21, 2015, 03:43 AM
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Pololu do a range of cheap switches. We use them for escapements in our single channel models.
Sparkfun stock them or any of the Robot stores. HK do a couple. I used to make them but the parts cost more than a finished commercial item.
Cheers
Phil
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Old Jan 21, 2015, 04:32 AM
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Well I feel stupid now. All it took was googling a bit differently. I've been googling "PWM controlled switch" or similar all the time...

Now I find tons of them. Thanks a lot for the feedback, now I can make more plans for future builds.

Oh, and PWM is what I'm looking for, not PPM.
Funny enough the switch from HK costs almost as much same as the headlights including the switch...

The Pololu switches look way better, configurable, smaller and without all the cables and connectors you always remove anyway.
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Old Jan 21, 2015, 04:39 AM
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Might as well let us know what you find so that people searching this here will get actual links to products.
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Old Jan 21, 2015, 05:51 AM
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I've found this one from Pololu that looks really promising.

Then there's the HobbyKing one.

Additionally, banggood carries one that is rated higher than the one from HK.

I haven't found anything on ebay worth mentioning.

The Pololu one is by far the most versatile one and it is also the cheapest. I'll probably order a few from my local distributor to try it out.
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Old Jan 21, 2015, 06:18 AM
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Originally Posted by jakestew View Post
Slipstick, you got PWM and PPM mixed up.
No I didn't. PWM normally means a signal with pulse varying between 0% and 100% to control something between fully off and fully on. That's not even close to how a servo control signal works, which is why we normally call it PPM.

Steve
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Old Jan 21, 2015, 06:28 AM
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Granted switches are cheap but if you would like navigation lights, not so cheap at £24 in lower link.
If you want nav lights with beacons you might consider the first link. It is DIY after all.
If you want nav lights with beacons or want to select from multiple pattern of lights you might fancy then consider posts #3 and #5 in the first link which show how simple it is with a Picaxe micro in Basic language.

If I can help?

Dave

http://www.rcgroups.com/forums/showthread.php?t=772567

http://www.4-max.co.uk/led-lights-deluxe.htm
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Old Jan 21, 2015, 07:06 AM
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Sorry Steve, nobody calls a standard servo signal ppm. Many receivers have both ppm and servo outputs.
Pwm duty cycle can be anything, nowhere is 100% implied. Conventional servo signals are a form of pwm.

Check the Pololus carefully, some dont have fets just a logic output. The one you linked is ok, low-side means the switch connects the load to neg, pos goes to the other side of the load.

Cheers
Phil
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Old Jan 21, 2015, 11:17 AM
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This link explain how to command multiple leds with one or 2 channels from your RX !
It's basic on Arduino

You can also try this example http://www.rcgroups.com/forums/showthread.php?t=1408754
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Old Jan 21, 2015, 11:18 AM
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Originally Posted by phil_g View Post
Sorry Steve, nobody calls a standard servo signal ppm. Many receivers have both ppm and servo outputs.
My word there are a lot of nobodies out there then, it's not just me. But given my obvious ignorance I'd better give up answering questions in here.

Steve
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Old Jan 21, 2015, 04:40 PM
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Just to clear up the confusion ...

PWM (Pulse Width Modulation) uses the width of the pulse to specify the parameter. In our case, it is what our servos (and other R/C peripherals) use as input to to specify a position.

PPM (Pulse Position Modulation) uses the time between consecutive pulses to specify the parameter. R/C systems generally use this to specify ALL or some sub-set of its channel positions over a serial link. An example of this is the serial link between a transmitter and a flight simulator. It is also commonly used as a "one wire" link between a receiver and a stabilization unit (i.e. Flybarless Controller).

And by the way, they are both analog signals.
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Old Jan 21, 2015, 07:15 PM
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Originally Posted by cbflys View Post
And by the way, they are both analog signals.
Great explanation cbflys. The last tidbit might confuse some people though.

PWM and PPM use digital signal levels, that is they are either on or off (high/low). However, unlike digital signals, the information is not contained in the high/low state. The information is contained in the time domain. Length/duty for PWM and position for PPM.

The time domain is analog in this case since the clock signal at both ends are free running and not synchronized. Thus the RX can't reconstruct the exact input value. There will always be noise and inaccuracies with analog signals like these.
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Last edited by jakestew; Jan 21, 2015 at 07:39 PM.
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Old Jan 22, 2015, 06:26 AM
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Originally Posted by slipstick View Post
My word there are a lot of nobodies out there then, it's not just me. But given my obvious ignorance I'd better give up answering questions in here.
You're very well respected on here Steve and you've made many helpful contributions over the years so please dont take it to heart, on this one occasion you simply got the terms transposed, thats all, its no big deal.
Cheers
Phil
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