# Picking up power from the track.



## Big4fan (Aug 29, 2010)

I have a question for all you electrical guru's. I have a 2.4ghz pin-hole camera that I am mounting in a Model Power Alco FA 2 Like this one: 

http://www.bing.com/images/search?q=scale+alco+f3&FORM=HDRSC2&&id=7E75231950AC96A7B1D7368FE93D8E59F20C7F2D&selectedIndex=26#view=detail&id=7E75231950AC96A7B1D7368FE93D8E59F20C7F2D&selectedIndex=0

I stripped the motor and the drive gears out of this loco to create space, but I kept the power pick-ups to power the video camera.

The pin-hole camera fits very well, I removed the lower forward light reamed the hole out just a tad, Got very good test pictures!

My question is picking up power from the track. The camera requires 5vdc so I have a 3 pronged voltage regulator to step the track down from 12vdc-13.8vdc down to 5vdc.

Here is my question: what happens if I run it on a layout that has the polarity reversed? Or a DC layout and the polarity is switched to reverse the locomotive direction?

If it were a motor or a fan it would run backwards. I am not sure how to remedy this situation.
Other than that issue she works great!

Thanks for your help!

J.C.


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## shaygetz (Sep 23, 2007)

It would smoke it...ask me how I know...hwell:

Your best bet would be an onboard battery--steady current, polarity safe.


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## NIMT (Jan 6, 2011)

Simple circuit.
Bridge rectifier to the voltage regulator to the camera.
You could also put some capacitors in before the regulator to maintain power during brief power outages.


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## Big4fan (Aug 29, 2010)

shaygetz said:


> It would smoke it...ask me how I know...hwell:
> 
> Your best bet would be an onboard battery--steady current, polarity safe.


I thought if it reversed the polarity the camera would act like a spotlight...LOL!


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## Big4fan (Aug 29, 2010)

NIMT said:


> Simple circuit.
> Bridge rectifier to the voltage regulator to the camera.
> You could also put some capacitors in before the regulator to maintain power during brief power outages.


I like that Idea! Can you diagram the circuit for me?


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## Big4fan (Aug 29, 2010)

Or anyone (for that matter)have a simple circuit design you would share with me?


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## gunrunnerjohn (Nov 10, 2010)




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## Big4fan (Aug 29, 2010)

Awesome! Thanks! Now if I can build it to fit in my Loco!


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## DonR (Oct 18, 2012)

GunrunnerJohn

Interesting circuit. Think I have a place
for it. LM7805 is an adjustable diode?

How physically do you adjust? 

Also it appears to be designed for use on 
a DCC layout.
The man with the camera asked
what would happen if used on a DC layout...and what
would happen if it hit a reverse polarity?

Don


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## gunrunnerjohn (Nov 10, 2010)

Actually, the LM7805 is a fixed voltage regulator, the requirement was for 5 volts.

The LM317 is an adjustable regulator. The regulators are actually power integrated circuits, not actually diodes.

The circuit shown will work with either track polarity, obviously if the voltage on the tracks falls below about 7 volts, the regulator will not be able to hold 5V, it requires about a 2 volt differential from input to output voltages.


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## T-Man (May 16, 2008)

To have a stable power supply you need capacitors on both sides The term is filtered DC. Normally I have a cheep chip and wing the size of the capacitor. For a camera you may want to research a little. I see about 1000 to 3000 uf before the regulator and 1 to 10uf after. Coming from a DC transformer maybe you don't need one.


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## NIMT (Jan 6, 2011)

The diagram GRJ put up is exactly what I had in mind, it works with DC, DCC, and AC.

Big4fan, 
If you can't get it small enought let me know I can build them pretty tiny.


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## Big4fan (Aug 29, 2010)

NIMT said:


> The diagram GRJ put up is exactly what I had in mind, it works with DC, DCC, and AC.
> 
> Big4fan,
> If you can't get it small enought let me know I can build them pretty tiny.


Sent you a pm... thanks


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## gunrunnerjohn (Nov 10, 2010)

T-Man said:


> To have a stable power supply you need capacitors on both sides The term is filtered DC. Normally I have a cheep chip and wing the size of the capacitor. For a camera you may want to research a little. I see about 1000 to 3000 uf before the regulator and 1 to 10uf after. Coming from a DC transformer maybe you don't need one.


Truthfully, you don't need input cap values nearly that large for filtering, the regulator has very good noise rejection. Obviously, it won't hurt anything, I might kick it up to something like 220uf, but I can't see putting a huge cap there. The cap after the regulator is to prevent it from oscillating under certain load conditions.


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## T-Man (May 16, 2008)

I only went with what I have found for circuits and read in a few places. That is good to know. 

I hope the camera survives.

John, you have an on board camera. What does that have for a power supply?


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## gunrunnerjohn (Nov 10, 2010)

I used basically the circuit I posted for the one time, that was after it ate several batteries rather quickly. I currently am looking for a likely locomotive to put the camera in, I'd like it to be hidden. I may try to put it into an RMT BANG.


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## NIMT (Jan 6, 2011)

I'm using a 330UF after the regulator to act as a buffer for intruptions of power.
I am building this new one with all SMD chips so it will be very tiny, Hope to get it to be smaller than a 1/2" square.


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## T-Man (May 16, 2008)

That is small. I stop at SMD. That is when you should buy already made.


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## sstlaure (Oct 12, 2010)

Mechanical Engineer.........brain exploding from EE talk......AAAAAAAAGH


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## gunrunnerjohn (Nov 10, 2010)

NIMT said:


> I'm using a 330UF after the regulator to act as a buffer for intruptions of power.
> I am building this new one with all SMD chips so it will be very tiny, Hope to get it to be smaller than a 1/2" square.


Do you have SMT layout capability? If so, where do you get boards? I have a project or two that I'd like to get boards for.


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## NIMT (Jan 6, 2011)

I make my own from stock blank PC boards, or some times strip boards work great. Just cut the traces with a dremel or knife. It's time consuming but gets the job done. I have some more tools on the way to acid etch that might be quicker.
I've been looking to get a good photo etching kit but have yet to find one.
There are several online PC board makers it's just there setup costs are too high for a few parts.
I keep working with smaller and smaller parts, I use a +3 magnifier and a very very tiny soldering iron, I've even been playing with liquid solder, crasy stuff but great for super fine work.

Scott, 
Sorry about the tech stuff, I know it rough on you!:laugh::laugh::laugh:

But it's for the trains!:thumbsup::thumbsup:


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## Carl (Feb 19, 2012)

Would a camera be sensitive to any possible voltage changes (surges for example?)


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## Big4fan (Aug 29, 2010)

Carl said:


> Would a camera be sensitive to any possible voltage changes (surges for example?)


I believe the voltage regulator would prevent a spike. While I am not sure I don't think a voltage drop would hurt it, I was mainly concerned with the polarity switching if I take it to the club or a friends layout. 

The camera itself is amazing!
I couldn't believe the clarity and resolution of these new pinhole camera's. 
It says it has 100ft of range (line of sight) which is about 3 times as much as I'll need.

This one actually has sound, but I am not going to be using that on this engine. Just need to pick up power from the rails at this point.

To distinguish the 'camera car" from the rest on the layout my son and I have decided to brand it D.T.& I. Complete with a red LED beacon powered from the rear truck.

I'll post up pics when we get it assembled and painted!

Thanks everyone for your input! This is a great hobby, and you all are a great bunch of guys!

J.C.


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## NIMT (Jan 6, 2011)

Yes the regulator and capacitors will eliminate all spikes in power.
Too bad you are not using DCC, I could set you up with a 100% controllable camera.


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## Big4fan (Aug 29, 2010)

I am using DCC here at home (Bachmann Dynasys), but the club (for now) and my buddy's layout are DC...


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## DonR (Oct 18, 2012)

Sean or John

Couldn't you just put a diode in each leg of the DC
power feed immediately before the camera and after
the other electronics you have suggested. That
would positively prevent any reverse polarity getting
to the camera no matter what was coming from
the track. But what would happen to your
bridge rectifier on a DC track?

Don


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## T-Man (May 16, 2008)

That is what the bridge is for. A bridge can be made with four diodes and they work better than one or two.

The bridge corrects the AC and reverse DC.


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## DonR (Oct 18, 2012)

T-Man

Big4fan runs DCC at home but wants to take the camera car
to his clubs DC layout. Sean's circuit would power the
camera on his DCC layout..my question was how does the
bridge rectifier react when powered by DC track voltage. Drawing
it out, it Looks
to me as if nothing would happen. The bridge rectifier diodes
would simply block DC regardless of which rail had +. No
current would reach the camera.

Maybe a DPDT switch (DCC or DC) with protection against
error would be possible.

Don


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## gunrunnerjohn (Nov 10, 2010)

Actually, the bridge rectifier will convert either + or - DC to the correct polarity, it's like magic. 

Note that one issue with this conversion is the voltage out of a bridge rectifier has NO common ground with the input voltage, you need to be aware of that fact.  For the camera application, that's not an issue.


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## DonR (Oct 18, 2012)

John

When I drew the bridge Rectifier out
I was seeing how DC track positive was passed but I couldn't
get my brain to accept that it wasn't blocking negative.
Now that you've hit me up side the head I see what you
mean...so Sean's circuit would automatically accommodate
whatever track current it was on, DCC or DC or even AC regardless
of track polarity. Like you say...and Doris Day (who is 90 today)
used to sing...It's Magic.

Hard to think of that beautiful lady at 90.

Don


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## NIMT (Jan 6, 2011)

I have all of the parts ordered and on the way to me. I have large versions of the parts needed here, just not super tiny SMD parts that I want to use.

I will post up what I build when everything gets here.


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