Electrical Whizzes--Control Panel Questions

[SpaceMouse]

I've decided to simplify my control panel by putting dual switches for every turnout. I already have SPDT MOM (on-off-on) switches for the turnouts and I plan placing SPDT (ON-On) right next to them. When you throw both switches the trunout moves and either lights a green LED for straight or a Red LED for turn.

Assuming I am using these LEDs

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=19142&item=5954600368&rd=1

I'm assuming I need to install resitor(s).

The questions I have are: 1) What size resitor do I need for these LEDs? 2) Can I create a seperate bus for the LEDs and put the resistor between the power pack and the bus? 3) Should the LED circuit be AC or DC?

[rrinker]

You might be simplifying things wiring-wise, but is everyone involved going to be able to understand how it works?
Simpler still, at least to OPERATE, would be a DPDT switch, and a single momentary contact pushbutton - toggle the DPDT, and pu***he button to line the switch.
Neither way gives exact feedback on the switch position - as soon as you throw the non-momentary toggle, the LED will change, event hough the actual switch points haven't been moved.
That said - use DC for the LEDs. Excessive reverse voltage, aka operating on AC, destroys LEDs. Resistor will depend on the pwer supply voltage being used. If you use a real 12V supply (by that I mean something cleaner than the typical train set power pack), then use 1K resistors. If you have a 5 volt supply, a 220 ohm resistor will work. 1/4 watt resistors are sufficient.
Bottom line, you want 10-20ma throught the LED. The formulat for resistance needed is Volts/amps, and 15ma is .015 amps.

--Randy

[SpaceMouse]

I'm not sure how your method is simpler. In my method, the two switches are next to each other and you pu***hem in the same sirection in one movement. The light then is always in sync with the actual position of the turnout, unless you only flip one switch. If they are out of sync for some reason, they will be re-aligned the next time you flip the switch pair.

Now to the unaswered question. Can I put a resistor in front of the bus so that the whole circuit is affected or do I need a resistor for each bulb?

I was planning to use the Hogwarts transformer for the DC accessories and the turnouts. It is rated: 17DCV 20ACV w/ Max 7VA total. Not clean as you say, but availible. Do I use the 17DCV to calualte the resistance needed? If so I would need a 1133 ohm resistor. (1K).

[davekelly]

Spacemouse,

I'll have to agree that Randy's method is simpler and I believe will be less expensive. Another method would be to use two momentary normally open push buttons to control the switch and a relay to work the indicator lights. The push button would throw the switch and energize the relay, thus the light would always be in sync with the switch. Sorry I can't be more specific on exact components, but I believe the Atlas snap relay would work, there's a diagram included with the thing, just substitute the two push buttons for the atlas controller (I think that's what its called - it's been awhile).

Of course, it may be easier to use something like the tortoise switch machine from Circuitron. You would control it with a toggle on the control panel and power the indicator lights from either the toggle or the contacts on the machine. A little more pricey, but I think you'll get more reliable operation (there's several threads on here that convinced me that tortoise is the way to go), easier operation (only one switch to play with) and the lights would be in sync.

[Leon Silverman]

For a 17 Volt DC power supply you should use 15.5 volts because the LED's operate at 1.5 volts, not zero volts (17 - 1.5 = 15.5) for your resistor calculations. Similarly, if your bulbs operated at five volts, you would size your resistor for a 12 volt drop (17 - 5 = 12).

[rrinker]

QUOTE: Originally posted by SpaceMouse

I'm not sure how your method is simpler. In my method, the two switches are next to each other and you pu***hem in the same sirection in one movement. The light then is always in sync with the actual position of the turnout, unless you only flip one switch. If they are out of sync for some reason, they will be re-aligned the next time you flip the switch pair.

Now to the unaswered question. Can I put a resistor in front of the bus so that the whole circuit is affected or do I need a resistor for each bulb?

I was planning to use the Hogwarts transformer for the DC accessories and the turnouts. It is rated: 17DCV 20ACV w/ Max 7VA total. Not clean as you say, but availible. Do I use the 17DCV to calualte the resistance needed? If so I would need a 1133 ohm resistor. (1K).

As Dave says, using Tortoises is probably the REAL solution. I know they're not cheap - this is why my layout isn't further along than it is, I can't afford to buy more than a few at a time, so I just keep plugging along. Plus last time I was ready to buy a few, the LHS was out of stock. Have a 6-pack coming now, that will allow me to do all but a few of the yard tracks, finally.
Back when I was a kid, we never had any sort of indicator lights on the control panel, just rows of Atlas pushbutton controls. Of course, maybe that's why I was able to run trains without running an open switch and my Dad couldn't, even though he built most of it...
You can't use just a single resistor, each LED should have its own. Check the output of that Hogwart's pack with a meter. 1K resistor is good up to about 20 volts or so. Who knows what the open circuit voltage of that cheap pack is. I know control isn't too great with it, it doesn't work very well at all as a jump throttle on my Zephyr. But you can always set it for somewhat less than full throttle.

--Randy

[davekelly]

Space,

Check this topic out. It discusses a switchmachine/relay combo made by Atlas.

http://www.trains.com/community/forum/topic.asp?TOPIC_ID=30420

[SpaceMouse]

Tortoises are out, partially because I'm using EZ track and mostly because I don't want to drop anymore money in this small track with the big one looming and the fear the kids will outgrow this one too fast. I have figured tortoises for the larger layout.

I'll throw the meter on the Hogwarts transformer tonight.

As for cost. I already have the SPDT MOMs and the SPDT (on-on) are only $.80 ea. I can't picture rebuying the DPDTs and the push buttons for cheaper.

But still, I guess I'm not understanding why Randy's method is simpler. In his scenario, you flip a switch and push a button. Not only is this two motions, but two differeint motions. In my method you throw two switches in one motion the same direction. So say you were switching tracks. On my layout this would involve 2 turnouts. Using Randy's method, it would be flick, push, flick, push. With my method it would be flick, flick.

I guess my resistance to Randy's idea is I don't fully understand it. Mostly it is the DPDT switch I don't understand. The way I understand it, the switch connects two circuits in each direction. But it has to be momentary to keep from burning out the turnout. That would mean that the LED would turn off.

Is what you are proposing is that the switch not be meomentary and the pushbutton is the momentary part. Wouldn't you then need a push button momentary for each side of the switch? You can see I'm probably not getting it.

Two other points. 1) The reason this is so important is twofold. First, nothing stops my son from playing with the trains faster than constant derailing. The Hogwarts derails if you look at it funny. The biggest culpret is coming into a turnout from the frog side when the turnout is improperly switched. Using my method above, a glance at the control panel will show whether an intended route is clear. This important because my son is autistic and he needs to be able to visually read the direction of the turnouts.

2) I guess I didn't say that the LEDs are on the track representation of the control panel so the lights indicate the open route.

[SpaceMouse]

QUOTE: Originally posted by davekelly

Space,

Check this topic out. It discusses a switchmachine/relay combo made by Atlas.

http://www.trains.com/community/forum/topic.asp?TOPIC_ID=30420

Thanks. Cool but not applicalble. I've already got EZ track installed. On my larger track, I've pretty much settled on tortoises.

[Leon Silverman]

Spacemouse:
There is another word of caution: I do not know how reliable those ratings on the power packs are. You might want to apply a multimeter to the terminals to verify the voltage available. Then apply a small load to the terminals, like a 12 or 18 volt light bulb and take another voltage reading to see if you still have that 17 volts. When a transformer or battery is connected to a load, you have an electrical current which has to pass thru that device. That current has to negotiate the internal resistance of that device. In doing so, that internal resistance lowers the voltage available across the terminals. This is the actual voltage your LED and resistor circuit will have to handle.
This is why you get a reading of 13 to 14.5 volts of a fully charged automobile battery when there is no load on it (everything turned off). Once you put a load on that battery (i.e. start the car) that terminal voltage drops to 12 volts.

[Seamonster]

If I understand you correctly, you have two toggle switches. One is locking and controls the lights, the other is momentary and controls the turnout. IMHO, it seems that would be a bit clumsy to use.

The problem with a toggle switch to control the lights is, as has already been pointed out, it doesn't indicate the true position of the turnout. You can flip the toggle switch but fail to activate the turnout and it will be indicating the wrong position. Or, someone could manually move the turnout, but the indication would not change, again showing the wrong position, and leading to a derailment. The only true way to show the position of a turnout is to operate the lights from auxiliary switched attached to the turnouts themselves. Many manufacturers offer these switches for their turnouts, and many modelers have come up with ingenious ways of adding them.

If you want to go with a toggle switch for lights and a momentary switch for turnouts, a pushbutton would be better than a momentary toggle. The pushbutton would go in the wire that attaches to the centre terminal of the toggle switch. That said, I'll admit that I'm using momentary toggles on my own control panel, but I'm using electronics to control the lights. When you get switches to operate the turnouts make sure they can handle the current. Twin-coil switch machines can draw a couple of amps momentarily so if the switch is underrated, the contacts could fuse together and burn out the coil.

You really should use a separate power source for the lights--much less chance of doing it wrong. That would mean using a double-pole toggle switch.

Here's how I calculate the value of a resistor for an LED. Subtract 2 from the voltage you're using to power them. Divide that answer by 0.015. That gives you the resistor value in ohms. Use the next highest standard 1/4 watt resistor value. For a slightly brighter LED, divide by 0.02, for a slightly dimmer LED, divide by 0.01. Yes, each and every LED has to have its own resistor, you can't use a common resistor for all. Yes, LEDs have to be operated from DC, not AC.

If you're not sure what I mean, you can e-mail me and I'll make a sketch for you.

Hope this helps.
...Bob

[SpaceMouse]

Okay, now I get it. Randy's method insures that the light and the switch are the same direction.

I just checked my source. I can get the LEDs and DPDT switches, but there are no push button momentary switches. Does anyone have a source for the push button MOMs or all of the above?

[rrinker]

I guess the other explanations made sense - think of it this way, a DPDT switch is just two SPDT switchs in a common body. The only way a DPDT makes a 'reversing switch' is with extra wires. With my method, you still don't get exact position reporting with the LEDs, the LED will change to the alternate route even if you never press the pushbutton to actually throw the switch machine.
Pushbuttons you can get a Radio Shack, or for better pricing a supply house like Mouser or Digikey.

Here's a crazy idea - it would mean making the control panel larger, probably, but you could use the Atlas switch controls (yes, I know you have Bachmann track, doesn't matter) and locate them on the diagram on the control panel so that the position of the control button indicates the route, no LEDs needed. Unless you have found some SPDT momentary toggles that actually stay facing the way you move them - all the ones I have ever seen snap back to center when you let go. If you have found such a beast, again you probably don't need LEDs, the switch handle will show the selected route. Always remember - KISS!

--Randy

[davekelly]

Space,

Please dont take offense and the only reason I mention it is that sometimes what I'm looking for and can't find is because I'm looking for an incorrect description. Look for pushbuttons that say "normally open." There should be litterally hundreds of these listed at any electronics supply place.

[Leon Silverman]

If you are going to the trouble to mount these switches on a control panel, I assume this panel will show a diagram of your track on it. I used no switches on the control panel of my previous layout. Instead I placed an single electrode (contact point) on both the straight track and divergent route. That electrode was connect to the appropriate pole on the coiled switch machine that would move the points to that direction. The center connection was connected to a bus that went to one terminal on the AC side of the power pack. The other terminal of the power pack was connected to a wire that was long enough to reach any of the electrodes on the diagram. The switch was thrown by merely touching that wire to the approriate electrode. I had an LED -resistor tied into the track power at each switch direction and positioned next to the approriate electrode. The electrode would light up as soon as the switch was thrown to give me an indication which direction the switch was thrown. By using different color LED's at each location, a uniform color along a route would assure me that the polarity did not switch from block to block.

[rrinker]

That's a great idea for switch position indicators, but it only works with power-routing turnouts. Atlas and Bachmann are not, and if you'd wire LEDs to them in this manner, they would both stay lighted all the time.

--Randy

[SpaceMouse]

QUOTE: Originally posted by davekelly

Space,

Please dont take offense and the only reason I mention it is that sometimes what I'm looking for and can't find is because I'm looking for an incorrect description. Look for pushbuttons that say "normally open." There should be litterally hundreds of these listed at any electronics supply place.

Good catch. I had ordered the push-buttons from Radio Shack and they had to order them for me. Sure enough when I called them back, they were planning on normally closed.

By the way. I've ordered everything for Randy's system, so now's the time to chime in and tell me what I should have done. I already have 20 SPDT MOMs going into the parts box, and i don't want them to get lonesome.

[Anonymous]

Spacemouse,

I solved this on my old layout by using relays and a DPDT on-off-on momentary contact toggle. The leds were used only on the diverging route to simplify wiring. If the led wasn't lit, the route was aligned through. One side of the DPDT went to the switch, the other to the relay. The Leds were garden variety running on 16 v AC for ten years no problem I used a resistor (1K, Off the top, I would have to look it up to be sure). Most of the leds I encountered were not real picky about voltage etc.

The other question I would have is: Is it necessary to have indicators for turnouts that you can see? I used this system only on turnouts that were hidden of otherwise inacessable. saved me a lot of time.

My two cents,

[davekelly]

Space,

Glad I was able to help. Normally closed push buttons would have been a bummer lol. Awesome that you are starting a parts box. It's amazing how useful they are, especially after a couple of years of getting bigger. Don't worry about your SPDT switches getting lonely. There is sure to be some project down the road where you will use them. I've got stuff in my box that have to be 10 or so years old and I'll be darned if I can remember what I originally bought 'em for!

[bpickering]

QUOTE: Originally posted by SpaceMouse
Good catch. I had ordered the push-buttons from Radio Shack and they had to order them for me. Sure enough when I called them back, they were planning on normally closed.

Radio Shack wins for convenience, in general, but you pay for it through the nose- both in price, and in product awareness of a good portion of the sales associates these days. (Especially when it comes to discrete components.)

I just got 40 SPST Momentary-On switches for ~$.40 apiece for my control panel. Go to Froogle (http://froogle.google.com and search on "SPST momentary". Radio Shack comes up as first on my list (YMMV), with >2< for $2.99. WOW! I then sorted on Price: Low to High, and get the switches I bought, from Marlin P. Jones & Assoc, for $.40 apiece.

I've also found some nice auctions on eBay, as well as other discount offers, using Froogle and/or bare-bones Google.

Can you tell I like Google? [:D]

Brian Pickering

[SpaceMouse]

I actually used Froogle to get everyting but the 1K resistors and the push button Moms. I'll drop $20 at RS. 16 push buttons and 40 1K resistors.

Could be worse.

[Anonymous]

QUOTE: Originally posted by Leon Silverman

By using different color LED's at each location, a uniform color along a route would assure me that the polarity did not switch from block to block.

Could you not just wire a Red LED/resistor across the block gap to show block polarity, if the polarity was different the LED would light...

You could also wire a 2nd Green LED/resistor across the block gap but to the other rail, if that polarity was different then it would light meaning polarity on the other rail was different...


Here's GOOD LED site
http://www.superbrightleds.com/led_info.htm

And SPACEMOUSE,
Your original idea would have worked very similar to the DPST w/N.O. pushbutton. You just approached it from a different prospective... One switch for LED the other for Turnout...

DC voltage is typically used for LEDs, but not absolutly the only way. When AC voltage is rated i.e. 17VAC the actual voltage is much more from the "Peak to Peak" on the waveform, its been awhile since school, but I think its 1.4 (?) times larger so for a little while your voltage is 23.8 volts.
http://www.ibiblio.org/obp/electricCircuits/AC/AC_12.html

scada

[Seamonster]

The problem with using an LED (or any light) across the block gap is that the voltage will vary, depending on how fast the train is going. If you size the resistor for maximum voltage, the light may not be bright enough for a slow train, and if you size the resistor for low voltage, when you crank up the throttle you may blow the LED or light.
...Bob

[Anonymous]

QUOTE: Originally posted by Seamonster

The problem with using an LED (or any light) across the block gap is that the voltage will vary, depending on how fast the train is going. If you size the resistor for maximum voltage, the light may not be bright enough for a slow train, and if you size the resistor for low voltage, when you crank up the throttle you may blow the LED or light.
...Bob

I should have thought about that....duh...

thanks
scada

[davekelly]

Man, did anyone expect that what seemed like a very simple situation would have so many different ideas - all of which have their own set of pros and cons?

[rrinker]

There's always a millon ways to do things. The wrong ways, and MY WAY! [:D][:D]

What else do you think we engineers do, besides come up with more and more ways to accomplish exactly the same thing? [:D][:D][:D][:D]

Note the smileys..I'M JOKING, PEOPLE!

This is why the engineer in me prefers Tortoises. Easier, simpler, toggles are usually cheaper than pushbuttons, and position indication is a no-brainer.

--Randy

[davekelly]

Randy,

Yup, I agree. But usually for me its- there's a million right ways to do things and then there is the one wrong way, which is usually the way I do it lol.

On the other hand, Randy, I'm sure you've spent time working on a way to do something, do it up with a bunch of stuff and then a month later see a way to do the exact same thing with one tenth of the components, one third the cost and half the time. I know I always do!!

[rrinker]

Constantly. That's why I switched from my original idea of using stationary decoders to run my Tortoises to using Rob Paisley's circuit, although I am not going to use pushbuttons. I keep thinking there MUST be a way to do it without any external circuit, but such a design continues to elude me.

Bottom line: I am going to eventually use a C/MRI system for signalling and dispatcher control. However, it MUST be possible to operate the layout WITHOUT runing the computer and/or control program. That menas, with the computer OFF, all turnouts must have local control enabled. If you look at Bruce Chubb's examples in last year's Signalling Made Easy series in MR, you can see it's easy to add an option to give the C/MRI and thus the dispatcher control over 'locking' or 'unlocking' the turnout for local control. But you will also see that with the very cheap and simple connection, UNLESS the controlling software is running, locla control will be disabled.
What I've done is built a simple open collector inverter with a pair of resistors and a transistor, that switches the common of the pushbuttons in Rob's circuit to ground, or open-circuits it. Thus, when power is on but the railroad computer is not running, the buttons work for local control. Power up the software, which will control the 'local power' line, and it can disable the locla buttons until the dispatcher makes the appropriate settings.
If anyone cares... LOL

--Randy

[SpaceMouse]

QUOTE: Originally posted by rrinker

There's always a millon ways to do things. The wrong ways, and MY WAY! [:D][:D]

I agree there's the way I do ti the first time. Then there's the way I do it the second time. And the third. And the fourth...