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Building a control panel. - Electrics - DC - Getting You Started. - Your Model Railway Club
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 Posted: Sat Dec 5th, 2009 11:22 am
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gordons19
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As progress continues on my layout, Eastwood Town, I was faced with having to build and wire a control panel for the lower lever reverse loop.  This was really a test bed for the main panel, which will be considerably more complex, but the principles will be just the same.  I am using Tortoise point motors and will eventually have route setting capability for the terminus, where you will be able to select any platform from the in road and set all the turnouts with just one rotary switch.  Likewise the out road can be selected from any platform.

In the past I have used solenoid motors and have built a diode matrix to enable route selection.  This needed a little time and care, but was really quite straightforward.  Because Tortoise motors are stall motors and depend on polarity reversal to change direction, route setting is a little more complex and in this case, requires 2 power supplies, wired together to provide a supply of +12v/0v/-12v.  This is what I have used here.

There are few components required.  Some 3mm LED's and mounting bezels, a small piece of pcb strip board, some 1k resistors and a single pole changeover switch.  The wire I have used is 10/0.1mm in three colours.  Red and black for the +/- 12v supply and yellow for the switching and 0v connections.  The switch is a miniature toggle from Gaugemaster and all the components are from Rapid.  I have used two types of 3mm LED's.  Green for normal circuits and red/green bi colour to show which way the points are set.




First stage was to print out a copy of the desired plan.  This can be done with tape or coloured pens, but I used WinRail software to draw a basic diagram.  This was printed in colour and then mounted onto 2mm mdf using spray photo mount.  Once this had dried, I sprayed the plan again with photomount and stuck on some 2mm thick plastic sheeting, that I bought from the local DIY store.  This forms a 4mm sandwich, which keeps the plan clean and stops the paper from tearing as you drill the holes in the panel.







Next stage was to drill the holes for the LED's and the three switches.  The spacing for the LED's was simply set by eye and marked on the plastic sheet with felt tip pen.  This is easily wiped clean if you find the spacing is not visually pleasing.  The 3mm LED's also have a small plastic mounting bezel which simplifies assembly.  I tried superglueing the LED's in place and not using the bezels in an earlier attempt and it was OK, but the bezels do look better and for a few pence each, the cost was worth it.

By the way, many thanks to Perth Buddy and others for their suggestions when I wasn't sure how to proceed. :thumbs

Once the plate is drilled you may fit the LED's and switches in place.







I decided to make a small pcb from strip board onto which I could mount the 1k resistors.  These are only required for the green route LED's which are permanently on.  The bicolours are connected via the switches and will show red or green depending on the route set.  Because I am using Tortoise motors, these do not need resistors as they are built in to the Tortoise circuitry.




All the wiring can now be completed.  I used 10/0.1mm wire in three colours to aid fault finding.  It will usually end up looking like a birds nest, so try not to worry to much.  With this number of LED's and switches spread over an area, it is difficult to keep it tidy.




I will always check the wiring as I go along, but before hooking up the power supplies, make one more final check all is correct.  Whilst the components are cheap, the loss of several hours of work can be infuriating.

As I said I used two RS power supplies wired together, but provided the output voltage and power is correct, then most 12v supplies will do.




One final check, switch on and voila! 

It was hard to take a decent pic and the red LED's are far brighter and denser than shown in this pic.  It is now easy to see which way the points are set and if they have fully closed.  Tortoise circuitry is such that the LED's dim when they are operating and do not glow to normal brightness until fully closed.  A very useful feature for hidden areas such as this reverse loop which will be completely hidden under the main layout.





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 Posted: Sat Dec 5th, 2009 11:38 am
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Bod
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A very neat job - from the top any way. :lol:

Do all the green LED's serve a purpose?

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 Posted: Sat Dec 5th, 2009 11:44 am
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gordons19
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Not as such.  They are only there to show the route.  As I said, this was more a test bed for me to see if what I envisaged could be done.  I think the green LED's show the route better visually, although as you say, they could be omitted.

I suppose it reminds me of my old boy racer days with a home built dashboard in my Cooper S.....or maybe, it was the John Travolta in me coming out. ;-)

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 Posted: Sat Dec 5th, 2009 12:41 pm
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Robert
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Index here it comes, both actually as it comes under forum content and equipment, broadly speaking.



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 Posted: Sat Dec 5th, 2009 05:42 pm
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ElDavo
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Neat work as always Gordon.

What I did for the route indication on Cramdin's panel (Mk II) was to hook the LEDs so that they only illuminated when the route was completely set. Effectively I powered them from the difference between the Tortoise supplies of two points. When both points are set for the route the LEDs illuminate but if one or other of the points is set wrong they are off.

That would work for the reverse loop I think. Just a thought.

Cheers
Dave

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 Posted: Sat Dec 5th, 2009 06:10 pm
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gordons19
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Funnily enough Dave, I was just laying in the bath, thinking about route illumination and having now seen the finished product, I'm coming round to your way of thinking and only having LED's lit when the route is set.  Means I'll have to rewire the thing, but I want it to be right.

I was also thinking about the equivalent of a diode matrix for Tortoise motors.  On the solenoid version, selecting the route powered the solenoid and changed the points.  This action overode the centre off momentary switch but it didn't matter as such. You could see the way the route was set via the LED's and the switch was centre off.

With stall motors, you are reversing the polarity, so setting the route changes the polarity and changes the points, but what happens to the switch?  You could still have the switch pointing up, whilst the point is set down....

Perhaps you can't have local control as well as route setting.  I'll need to go back and check out the schematic..:???:

http://www.awrr.com/matrix.html

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 Posted: Sat Dec 5th, 2009 07:02 pm
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Bod
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Whatever you decide Gordon, please keep us posted here. Currently I use a little schmatic with just a stud/probe system to operate solenoid type motors. When I go up into the loft I think it will be with tortoise type motors and will probably need some sort of route indication like yours.

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 Posted: Sun Dec 6th, 2009 10:23 am
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gordons19
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OK, done some more testing and I have some questions re LED's and Tortoise motors.

I seem to recall reading somewhere that the resistance of a Tortoise is around 600 ohms.  They say you can wire as many LED's in series as you wish, but each LED will drop the voltage by around 2v.  The maximum I can get away with is three off 12v, so to run 5 or more will require a higher voltage.  The problem I have is that the number of LED's I have on each operation of the switch can vary and may be only a couple.  In that case the Tortoise motor will see a different voltage depending on how many LED's are wired in series.

I have tried wiring 5 in parallel and they work just fine, but reading about LED parallel arrays it suggests a resistor of at least 1w.  When wired in series the current is much lower at just 1/8w.

Will there be any problem putting 1w through the built in resistance of the Tortoise?  The last thing I want to happen is to burn out part of the motor.  Seems fine to me, but I'm not an electronics engineer....

Anyone able to give some guidance?

Thanks again for your help.

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 Posted: Sun Dec 6th, 2009 10:56 am
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Sol
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Gordon, the Tortoise will work on 6v so it means only 3 LEDs in series using a 12v supply but normally only one is used as per the circuit diagram that comes with the Tortoise. The LED normally is to indicate the direction the point is set & that means 2 per point.

Using a maximum of 12v thru the tortoise with internal resistance of 600 ohms, the maximum current can only ever be 20mAmps & by adding LEDs, the current can only drop in total as LEDs give resistance as well. The normal wattage in the tortoise is .24W so reducing current because of adding LEDs, reduces wattage as well.

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 Posted: Sun Dec 6th, 2009 11:03 am
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gordons19
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Thanks Sol, but apologies for my lack of electronics knowledge, does your answer mean it will be OK to run 5 LED's in parallel directly to the Tortoise motor or not?..:oops:

If it is OK to run 5 (I've had 5 running for 30 minutes or so without problem), is there a maximum number that could be hooked up in parallel from the calculation you have made?

 

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 Posted: Sun Dec 6th, 2009 11:12 am
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Sol
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Gordon, why do you want to run 5 LEDs in parallel with a device that moves points? That is something completely new to me.
I think you need to draw the circuit & post in on here.

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 Posted: Sun Dec 6th, 2009 11:21 am
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gordons19
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If you see the small track plan in this thread, you will see there are three Tortoise motors controlling the three turnouts.  Originally I had bicolour LED's hooked up to the turnouts which were red or green dependant on the the route set.  All the other LED's were permanently on to show the route.  As I said this is also a test bed for the main terminus panel which will have 30+ turnouts and multiple routes.  I realise now that having all LED's lit is a little confusing and having now considered Eldavo's input, I'm going to change the wiring to only illuminate when the turnout is set for the right direction. 

Taking the turnout which gives access to the reverse loop from the downline at the top of the diagram, you will see there are 5 LED's on the downline which will need to be lit when the turnout is set correctly.  Changing that turnout to access the up line will only light 1 LED as the next two will be connected to the trailing point from the reverse loop.

Hope that makes sense.....




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 Posted: Sun Dec 6th, 2009 11:28 am
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Sol
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Gordon, IMO you do not need all the other LEDs to show the route, that is what the Red/Green do.

Now if the Leds went on/off as the train went thru the route, that is another story!

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 Posted: Sun Dec 6th, 2009 11:35 am
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gordons19
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Sol, just edited my pic to show what I mean.  Of course it's no problem on a small panel like this, but the main terminus panel may well be 2' long as there is a lot of track/routes contained in that area of 18' x 3'.  There I really want to show the whole length of the platform and that all is correctly set.  It may not be the usual way of doing things, but what the heck, it makes life more interesting....:lol:

I've only done it on this panel to prove to myself it can be done....

I really would be grateful if you could just confirm whether hooking up 5 or more will be OK?

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 Posted: Sun Dec 6th, 2009 11:46 am
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Sol
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OK, put 6 in series & parallel them across the motor.
If you have less, add 200 ohms per Led that is less than 6.
In other words - 4 LEDs + 400 ohms; 2 LEDs + 800 ohms.

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 Posted: Sun Dec 6th, 2009 12:01 pm
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gordons19
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Thanks Sol, that's brilliant.  Just hooked up six as you suggest and it's great.  :pathead

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 Posted: Sun Dec 6th, 2009 12:26 pm
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Sol
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Good then Gordon, if it works to your satisfaction, I am happy then that I have not completely confused you.

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 Posted: Sun Dec 6th, 2009 01:42 pm
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gordons19
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Just out of interest then Sol and if nothing else to satisfy my curiousity, are you saying I couldn't have wired five in parallel as I originally asked?  As I said it seemed to work OK, but then I didn't know what was going on inside the Tortoise....;-)

Of course you've solved the problem and I am very grateful, but just as part of my learning curve, I want to try and understand this answer you gave...

"Using a maximum of 12v thru the tortoise with internal resistance of 600 ohms, the maximum current can only ever be 20mAmps & by adding LEDs, the current can only drop in total as LEDs give resistance as well. The normal wattage in the tortoise is .24W so reducing current because of adding LEDs, reduces wattage as well."

I wasn't sure if you was saying it would work or wouldn't...

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 Posted: Sun Dec 6th, 2009 05:58 pm
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Geoff R
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gordons19 wrote: OK, done some more testing and I have some questions re LED's and Tortoise motors.

I seem to recall reading somewhere that the resistance of a Tortoise is around 600 ohms.  They say you can wire as many LED's in series as you wish, but each LED will drop the voltage by around 2v.  The maximum I can get away with is three off 12v, so to run 5 or more will require a higher voltage.  The problem I have is that the number of LED's I have on each operation of the switch can vary and may be only a couple.  In that case the Tortoise motor will see a different voltage depending on how many LED's are wired in series.

I have tried wiring 5 in parallel and they work just fine, but reading about LED parallel arrays it suggests a resistor of at least 1w.  When wired in series the current is much lower at just 1/8w.

Will there be any problem putting 1w through the built in resistance of the Tortoise?  The last thing I want to happen is to burn out part of the motor.  Seems fine to me, but I'm not an electronics engineer....

Anyone able to give some guidance?

Thanks again for your help.



Hi Gordon,

The panel is looking great, and good to see that Sol has given you a solution for a number of LEDs wired across the tortoise motor. I think in the above you are asking about LEDs in parallel but connected in the line to the motor? There should be nothing to worry the tortoise. It is the tortoise motor which will limit the current. 12v directly across it would mean that it draws 20mA if it has a resistance of 600ohms. Putting parallel LEDs in line with the motor will simply drop its operating voltage to about 10v and therefore slightly lower the current it takes - may not be in direct proportion as the motor may not appear like a linear resistor. Anyway, you now have something less than 20mA flowing through the motor and also shared through 3, 5, 6, 7, ... however many LEDs you have paralled together. The problem will be brightness of the LEDs. The more you put in parallel the less current going through each, and therefore the less light emitted.

In summary, you can keep on adding parallel LEDs in the line to the motor without harming the motor at all. Just watch the LED light level dropping as you go from 1 upwards. I wonder how many you can get to before you lose illumination altogether?

Cheers

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 Posted: Sun Dec 6th, 2009 07:23 pm
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gordons19
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Thanks Geoff for the information.  I guess what you are saying is that there is likely to be an illumination difference between 1 LED and 5 LED's when they are wired in parallel across the motor.

Wiring them in series with different resistor values as Sol has suggested, will give an even current flow through the LED's and as such the level of brightness will be more consistant.

Railway modelling is a wonderful hobby and the electronics side is rapidly becoming very interesting for me.  I just wish I'd listened more in college and not been distracted by girls and motor cycles.....but on the other hand, you're only young once.;-) 

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