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Walthers traffic light circuit

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  • Member since
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Walthers traffic light circuit
Posted by MisterBeasley on Sunday, August 24, 2008 4:32 PM

I've picked up a few of the Walthers traffic signals at their sale prices recently, but I've never seen their controller electronics on sale.  Since it's a hefty $35, I tried to use a circuit kit from Bakatronics.  Despite my own ineptitude, installing the wrong resistors in a couple of places, ripping the conducting foil off the board and losing parts, I was able to get the circuit working exactly as it's designed.

Unfortunately, it looks to me like the designers of this circuit, and others I've looked at online, decided to wire all the cathodes of the LEDs together, while Walthers has all the anodes wired together.  Since there's only one common "black" lead coming out of the signal, I can't simply reverse the leads to get the right light to come on.

Has anyone else noticed this, or found a solution?  It seems like there should be a way to do this easily, but I can't see it.

It takes an iron man to play with a toy iron horse. 

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Posted by lonewoof on Sunday, August 24, 2008 5:07 PM

I think, unfortunately, there is NOT going to be an "easy" way. You could build up a circuit by adding a couple of resistors ant a transistor for each light, but you'd have to have a piece of perf board or similar to build it up on.

Easiest way would seem to be -- get into the lights themselves and rewire them. (I haven't seen one; if they are cast/molded in one big block, all bets are off)! Any possibility of cracking one open, rewiring the LEDs, then gluing it back together?

/Lone

 

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Posted by richg1998 on Sunday, August 24, 2008 5:41 PM

It is rather simple but I guess this is what you have. All the anode leads are connected together. The three cathode  signal leads have to go to minus voltage to light with a series current limiting resistor.

Rich

If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.

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Posted by nedthomas on Sunday, August 24, 2008 6:00 PM
If you have some experance in wiring try a CMOC chip 4049 Hex Inverting buffer. Max voltage is 15 volts and will handle enough current for the Walthers crossing gate. Use a small PC board from Radio Shack. The chip has 6 inverters so if you only use 3 tie the unused inputs to ground.
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Posted by gandydancer19 on Sunday, August 24, 2008 6:36 PM

 nedthomas wrote:
If you have some experance in wiring try a CMOC chip 4049 Hex Inverting buffer. Max voltage is 15 volts and will handle enough current for the Walthers crossing gate. Use a small PC board from Radio Shack. The chip has 6 inverters so if you only use 3 tie the unused inputs to ground.

Now that sounds interesting. I am a retired electronics technician but not a circuit designer/engineer. I do have some limited experience with digital circuits. And, I have a Walthers traffic light that I was hoping was common cathode. (That is one thing the reviews don't tell you.) I bought it on sale but haven't looked at it yet. Isn't that the way most of us buy things?

Thanks for the tip.

Elmer.

The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.

(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.

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Posted by MisterBeasley on Sunday, August 24, 2008 6:39 PM

 nedthomas wrote:
If you have some experance in wiring try a CMOC chip 4049 Hex Inverting buffer. Max voltage is 15 volts and will handle enough current for the Walthers crossing gate. Use a small PC board from Radio Shack. The chip has 6 inverters so if you only use 3 tie the unused inputs to ground.

That might just do the job.  Is the 4049 an analog inverter, i.e. +V -> -V, or is it a logical inverter, i.e., +V -> 0?

6 inverters would be perfect, because I've got North-South lights and East-West lights.  They aren't mirror images of each other.  The circuit shuts off one green and turns on the yellow briefly, while holding the other side's red on, just like a real light does just as you're coming up to it.

This is the Bakatronics kit I bought:

http://www.bakatronics.com/shop/item.aspx?itemid=341

 

It takes an iron man to play with a toy iron horse. 

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Posted by loathar on Sunday, August 24, 2008 7:00 PM

Dallas Model Works has the Walthers unit for $27 if you sign up for a free membership with them. They have the traffic lights dirt cheap too.

http://www.dallasmodelworks.com/products/product_detail_accessories.asp?ItemNumber=WA-933-2306

 

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Posted by MisterBeasley on Sunday, August 24, 2008 7:20 PM
Thanks for the info.  At this point, though, it's a grudge match.  By Grabthar's Hammer, I'm gonna make this thing work.  A 4049 is only 99 cents online.

It takes an iron man to play with a toy iron horse. 

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Posted by Mark R. on Sunday, August 24, 2008 8:47 PM

I built that Bakatronics controller myself and it actually worked pretty good .... on a 9-volt battery. Not wanting to have the thing battery powered I tried numerous 9-12 vdc power supplies and the circuit would operate very erratically. That's when I discovered it is very sensitive to spikes of a non-filtered power supply. Having constructed a dedicated FILTERED power supply for it, it once again works fine.

I like the idea of the inverter. I came up with a simple circuit that allowed each output to control an smt relay which in turn controlled what-ever out put I needed to throw at it. This way the relays could be used to control more than one intersection and numerous signals around the layout.

Mark.

¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ

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Posted by Mark R. on Sunday, August 24, 2008 8:59 PM

FWIW - This is how I solved the problem ....

For this application, anything from 5 to 15 volts would be fine.  Be sure you match the voltage requirements of the relay to the supply voltage.  if you use 12 volts for the circuit, use a 12 volt relay. The op-amp can be a LM741 (available at Radio Shack).  If you get an LM1458 (also available at Radio Shack), it has two amps on one chip, allowing you to reduce the number of components by combining circuits on one board.  You could even use an LM324 which has 4 amps on one chip. The potentiometer could be a small PC mount version.  Once it is set, it can be left alone.  You could use one potentiometer for all the reference voltages to all op-amps as the current draw is minimal and they all need the same reference voltage.  The reference voltage just needs to be set below the incomming voltage from the traffic light controller (to trigger the comparator).   If you know the output voltage of the traffic light controller, just set the reference voltage (controlled by the potentiometer) a little below this.  For instance, if the output of the traffic light controller is 1.5 volts, you could adjust the potentiometer to give you a reference voltage of around 1 volt. The basics behind the comparator are this.  When the voltage on the positive input goes higher than the voltage on the negative input, the output goes high (or puts out a positive voltage).  Thus, when the output of the traffic light controller is low (or off), the positive input voltage is lower than the reference voltage (the negative input) and the output of the op-amp is low.  When the output of the traffic light controller switches to high (or on), the voltage on the positive input of the op-amp is higher than the reference voltage on the negative input and th output of the op-amp goes high (or on). All resistors can be 1/8 or 1/4 watt unless noted.

 

 

Mark.

 

 

¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ

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Posted by MisterBeasley on Sunday, August 31, 2008 10:15 AM
Well, the 4049 really isn't what I want.  It works OK, but its function is to logically invert the signal, digital rather than analog.  So, instead of getting -V when I put in +V, I get 0 when I put in +V, and +V when I put in 0.

It takes an iron man to play with a toy iron horse. 

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Posted by gandydancer19 on Sunday, August 31, 2008 8:24 PM
Thanks for the up-date Mr.B

Elmer.

The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.

(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.

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