Wiring a Simple Diode Matrix

Step by Step for Beginners
By Stephen J Chapman.

If you're a beginner to Model Railways or a novice when it comes to model railway wiring then my explanation of how to wire up turnouts in my article Diode Matrix Turnout Control may not make much sense to you. To help you out I will now go into more detail on exactly how the introductory circuit shown in figure five of that article actually needs to be wired up so as to provide a three button route control for the track plan shown in figure three of the article.

First, let's show the track diagram again so that we know what the track looks like that we are talking about wiring up.

figure three ladder

We have one track coming in from the left leading through two turnouts to become three tracks at the right. We label these turnouts A and B and the routes from the single track on the left to each of the tracks on the right 1, 2, and 3 respectively. Each turnout has a normal (straight) road and a curved (reversed) road. So now we have the terminology straight so we know what we are talking about.

Let's start by considering what components we need to wire this track layout with a diode matrix.

Here is a diagram that shows how we need to use the wire to connect these components together to complete our circuit.

complete wiring diagram

So now let's go through the process of wiring up your point motors in accordance with this diagram. The first step is to take a wire from one terminal of your AC power supply and connect it to all of the connections on one side of all of your point motors. This is the return wire that will complete all of our point motor circuits. The other terminal of your AC power supply needs to be connected to one side of all of your push button switches. You will need to do this part of the wiring regardless of how many point motors you have and whether you intend wiring each point motor separately or using diode matrix route control.

So now let's consider how we need to wire the particular elementary track plan that we are looking at here which is the simplest setup that can use a diode matrix.

Push button one (which will set route one through the turnouts) only needs to set the point motor on turnout A to normal. So all we need to do here is run a wire from the second connection on the push button to the second connection on the normal side of point motor A. (You may need to experiment with supplying power to either side of the point motor before you start wiring in order to work out which side is which).

Push button two needs to set the point motor on turnout B to reversed (the curved route through the turnout). As this is the only push button that will do this we can again take a wire directly from the second connection on push button two to the second connection on the reversed side of point motor B. This push button also needs to set turnout A reversed but is not the only button that will be doing this so we don't connect a wire directly from the push button to that connection on the point motor, instead we place a diode somewhere in this wire ie. the wire goes from the second connection on button two (the same one we just wired to point motor B reversed) to one end of the diode and then a wire from the other end of the diode goes to the second connection on point motor A reversed.

We wire button three similarly to the way that we wired button two except that in this case the direct wire goes to point motor B normal instead of reversed. So once we're finished we should have two wires coming out from each of push buttons two and three and two wires going into point motor A reversed.

The diodes should have a marking on one end so that you can tell which end is which. It doesn't matter which way around they are wired as long as they are all wired the same way around. The diodes only allow power to flow one way so that the power that flows through one diode to point motor A reversed is unable to flow through the other diode (since they both face the same way) and is therefore unable to reach the point motors on that side (which are intended to be operated by the other push button).

The only time when the direction of the diodes matters is if you decide to insert a capacitor discharge unit between the AC power supply and the circuit shown. As the CDU converts the AC to DC you will need to make sure that the current is flowing the right direction to get through your diodes. The easiest way to check this is to wire it up and see if it works. If it doesn't then you just swap the wires on the output side of your CDU over to be the other way around.

So that's a detailed explanation of how to wire up the diode matrix shown in figure five. Basically the diagonal lines on the diagram represent the wires between the push buttons and the point motors. Where the diagonal line contains a drawing of a diode, the wire between the button and the point motor also needs to contain a diode. It should be relatively simple for you to work out the equivalent wiring required by any of the more complex diode matrices that you develop.

figure five diode matrix
For more info see my article Diode Matrix Turnout Control.
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Copyright Stephen Chapman