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Reversing Controller

6420 Views 26 Replies 6 Participants Last post by  toddalin
In a recent acquisition, I found in the box an Aristo Craft Reversing Controller, model ART-11090-02. One of my little projects was to set up a trolley line that went from one end to the other, sat for a few minutes, then returned. I am hoping this device may do the job. However, I have no documentation or any idea how to set one of these up.

First, will this do the job? If so, how do I hook it up?

If this is not the correct device, how do I set this type of operation up?

If this is not the right forum to ask, please point me in the correct direction.

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If that doesn't work for you, you can make your own for a couple dollars if you are handy with a soldering iron. I've made and use four with the included schematic.

See pics below:

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Posted By krs on 09/30/2008 5:28 PM
Yes -

The circuit is extremely basic but I think it will work fine if you set it up correctly.

The 555 timer is configured as a multivibrator with a very low pulse rate - so the relay will switch and change polarity based on the RC time constant of the 200 mf capacitor and the setting of the 500K pot.
That means you can agjust the pulse rate.
The idea is to make the pulse rate a bit longer than the time it takes the train to go from one end to the other - once the loco passes the diode at the end of the track it will stop because the diode will block the current. As soon as the timer reverses the track polarity, the diode will conduct and the train will head back in the opposite direction where the whole thing repeats itsel with the other diode.

So you set the switching time of the unit equal to the time it takes to travel from one end of the track to the other PLUS the time you want the engine/train to stop at each end before reversing and travelling back. Does everything it's supposed to do with a very simple circuit - but of course if the relay switching and thus the reversal happens before the loco reaches the diode section, then the train would reverse immediately which is not exactly good for the engine.

You can get more details here for example:

Rough calculation indicates the switching time of the relay can be adjusted from about 6 seconds to about 75 seconds.

You are correct on all accounts.

What is not mentioned is that with this circuit, using a readily available 6 volt relay (that can easily handle the amperage of a train though its contacts), you need to be running the trains at a minimum of ~8 volts. I always run my trains at 10+ volts so this was not an issue when I came up with the circuit. If you want to run your trains with less than 7-8 volts, you would have to modify the circuit with an additional power supply tap to power the electronics, in addition to the power that actually feeds the rails.

If you want to increase the timing interval, you can increase the values of the capacitor and/or pot.

Some 555 chip/relay combinations can be "finicky" where the chip won't fire, or sometimes misfires. This can usually be fixed by putting a "backward" diode acoss the relay coil. It really depend on the relay and chip manufacturers specifications.
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Posted By Torby on 09/30/2008 7:00 PM
You want the diode across the coil, not the contacts
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Correct. Sometimes I also find it helps to put a capacitor here or/also. In the case of a capacitor, I usually find the value is not critical, and can be on the order of 20 - 100 mfd. In this case you need to be sure that you have the correct + and - in accordance with the relay coil (not reversed like the diode) and that the capacitor voltage is higher than the relay voltage.

There is actually about a 1.5 volt drop from the chip to the relay so the relay really gets about 4.5 volts. This is enough for most 6 volt relays. (I've used literally a couple dozen driven off 555/556 chips). If you can find them you could even use a 4.5 or 5 volt relay, providing the contacts can handle the current of the trains.
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Posted By krs on 09/30/2008 10:10 PM
Toddalin -

I must admit I didn't realize that was your circuit - I thoght it was the schematic of the Aristo unit. I just looked at the diagram - didn't read the text.

But as a former commercial designer, I'm curious about a few things.

1. Why do you think a back-emf diode is not required across the relay coil? The 555-type timers I'm familiar with don't provide an internal protection diode and without back-emf protection and the inductive load, the output transistor won't survive for long.

2. Pin 4 and 5 in your circuit are not connected. If not used, pin 4 should be connected to the positive supply and pin 5 should be connected to ground through a 0.01 mf (microfarad) capacitor to eliminate electrical noise.

3. I think a 220 mf capacitor would be more appropriate for the timing capacitor simply because 220 mf is a standard value where as 200 mf is not.

And finally - since it looks as if people want to build this circuit for their own railroad, it would be helpful if you took the time to list the specific components required with the appropriate RS part numbers.

1) Of the literally 2 dozen of these I've made, only a couple have required me to add the back-emf diodes for proper, long-term operations. If it ain't broke, why fix it?

2) Of the literally 2 dozen of these I've made, I've only found it necessary to add the 0.01 cap on pin 5 in one case and that was for an occasional glitch problem. About 8 out of 10 schematics I've reviewed omit these parts too.

3) As I noted, the part values aren't critical. I use parts from cannabilized VCRs, TV sets, DVD players, etc., and Internet surplus sales, so I gets what I gets.

All component values (except the relay which is obviously 6 volts as mentioned) are included in the schematic. If the named part is not in RS stock, use the next "bigger" value and that should do the trick.

These are the circuits that drive my module for the Del Oro Pacific. They use 9 556s and one 555. None have the reverse diodes or 0.01 mfd caps. These drive 10 of the 6 volt relays.

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Posted By krs on 10/01/2008 12:31 PM
Thanks for your reply toddalin -

Reminds me of a saying we had in our electrical engineering group: "Design marginal circuits and fame and fortune will be yours"

As to components used, you don't have any specs on the bridge rectifier or the voltage regulator for instance.
Will 1N914 diodes do for the bridge rectifier (after all they are cheap and I have almost a 100 of them in my component box); and what about a 78L06 6 volt regulator, I have a few of those lying around also.

Schematic does say to use a 6 volt positive regulator. To me, a rectifier is a rectifier is a rectifer and even the smallest of these are rated at 1 amp and will have plenty of capacity. You can use four 1-amp (4000-series) diodes to form the bridge.
Posted By krs on 10/01/2008 4:03 PM
I picked the 1N914 diode and the 78L type 6 volt regulator on purpose to make a point.

A rectifier is not a rectifier is not a rectifier......if they were all the same why do you think there are thousands of different types?

The 1N914 dide can comfortably handle 100ma of current, the 78L type voltage regulator is already maxed out at 100ma - so I went looking for a 5 or 6 volt relay with contacts that can handle 3 amps or better at 24 VDC.
Radio Shack didn't show any on their web site, so I looked at All Electronics, a surplus place. Of the 46 diferent relays they have listed, only one meets the requirements of 3 amp or better DPDT contacts and a 5 or 6 volt coil. This one:

Trouble is that the coil has a resistance of 50 ohms, so the relay will draw 120 ma when operating and you exceed the rating of both the diode and the 6 volt regulator that I listed.

You could try Mouser and Digi-key or active Electronics or Future Electronics or any number of others to try to find a relay with a higher coil resistance, but moving 3+ amp contacts takes a certain amount of energy and you are not going to find a low-current relay that will do that.

My point is simply that you can't just throw a bunch of components together in a circuit and hope that everything will work out in the end.

Maybe you know how to select each one and which component parameters are important and which one are not in a specific circuit, but I'm sure many people who might want to build this unit, cannot.

As I noted, use 4000 series diodes.

The rectifiers I typically see are 1 amp or more. The 555 chip can handle up to 250 milliamps, and I've used them to directly driver BIG relays (10 contacts at 120 volts) that draw 150 milliamps with no problems.

You could certainly use this relay (even has the reverse diode built right in) , (though I was getting 4pdt 5 amp, 6 volt relays from these guys @ $0.60/each and got about 20 at the time).


Aromat S2EB-5 relay features a polarized 130ohm 5VDC coil and four separate sets of contacts giving the equivalent of DPDT contacts. Contacts are rated 4Amp @ 250VAC or 3Amp @ 30VDC. Has 12 PC pin terminals. Sealed case is 1.11" L x .48" W x .40" Tall. Worth about $15.00. Brand New! G15227

Don't like their stuff?

This works out to 120 milliamps and is within the capacity of the 555 chip:


Or, two of these could be used for a dpdt:


Or two of these to make a dpdt:

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Posted By krs on 10/01/2008 4:03 PM

Trouble is that the coil has a resistance of 50 ohms, so the relay will draw 120 ma when operating and you exceed the rating of both the diode and the 6 volt regulator that I listed.

Actually, no it will only draw ~90 ma.

Remember that you only get about 4.5 volts out of the chip. (4.5 x 4.5)/50/4.5 = 90 ma

Furthermore, ANY rectifier or RECTIFIER diode or 6 volt regulator purchased at Rat Shack has the necessary capacity. Switching diodes (that you selected) are not typically used as rectifiers.
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If anyone wishes to build a reverser and is having trouble finding a suitable relay, the included schematic will allow you to use the A/C tap on your power pack or any dc source of ~14-22 volts to power the electronics. This costs no more and does have advantages. First, you are not limited to the 7-8 volt minimum on the track as you would be using the prior diagram. Next, it gives you access to a much wider variety of relays so you can more easily find what you need. Use a 12 volt relay (very common) and a 12 volt regulator, and you probably can get all the these parts at Rat Shack without problem. Or, get them surplus and save even more money.

Again, you may need to put the reversed diode across the relay coil to prevent eratic behavior. Use a 1 amp (4000 series) diode for this.

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Posted By chrisb on 10/03/2008 5:52 PM

I put the below list together. For the items with a question mark, is more description needed to go into RS pick up all or most of the parts?
Please edit the list as needed. Is a pot a resistor? Thanks.

bridge rectifier ?
capacitor 100 mfd 35 volt
capacitor 10 mfd 16 volt
capacitor 200 mfd 16 volt
regulator positive 6 volt
resistor 1 k ohm
resistor 47 k ohm
pot 500 k ?
555 chip ?
relay coil ?
relay armature ?

Lets hook it up using the a/c tap as I showed in the second diagram. Then you can get all the parts at Rat Shack.

The bridge rectifier at link:

Because we are going to use the a/c tap, we would like a little more filtering on the power supply so the relay doesn't "chatter." Instead of using the 100 mfg 35 volt cap, use this 470 mfd cap:


And instead of the 10 mfd 16 volt cap, use this 47 mfd cap:

Use this diode to go across the relay coil if necessary:

Lets use a 12 volt relay. This includes the coil and armature and can switch 5 amps so should be plenty for a single engine to go back and forth:

With a 12 volt regulator:

The 555 chip:

Lets use a 1 meg pot as they have it and this will increase the total time up to about ~2.5 minutes:

And you can use this 220 mfd instead of a 200 mfd cap. This should take cycle time from anywhere from a minimum of about 8 seconds up to about 3 minutes:

Questions? Just ask.

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