Orwell St Johns

ORWELL ST JOHNS A Modern Image Layout in OO
Home Gallery Track Plan About OSJ Exhibition Details Rolling Stock Diary Wiring Buildings Links	The point work on the main lines and also the fiddle yard is all controlled by a form of route setting. Signals are currently manually set although it is hoped that they will be integrated into the route setting at some point. Loco control is down through conventional DC with cab control being deployed throughout, in addition to this, there are a number of relays that power sections of the track depending upon which route are set by the points. Designing the system to run the route setting wasn't as simple as was first thought because potentially we had up to 11 point motors that could be thrown at the same time. To add to this we also wanted to integrate the signals into the route setting. The initial problem was how to potentially throw 11 points at the same time, most CDU claim to throw 3 or 4 at most and the amount of power required to throw 11 would be quite great. We therefore adapted a method deployed by one of our members down at IRMA for reliable point operation as can be seen in figure 1 below, this originally only had one capacitor, but a second was added to help improve performance and help reduce a possible surge in current required from the power supply. figure 1 When switch SW1 is thrown to activate PM2 capacitor C2 discharges and give a short but sharp bust of current to throw the point, power will pass-through PM2 until capacitor C1 is charged up. When SW1 is thrown to activate PM1, the opposite happens, C1 discharges and power will pass-through PM1 until capacitor C2 is charged up. Where a pair of facing points need to be thrown together the values of C1 & C2 are simply doubled to 2000uf with the point motors being wired in parallel. For route setting to work switch SW1 is replaced by a relay that is capable of handling the current used by the point motors (or coils as the really are!) The relay itself is driven by the output of a TTL circuit, this TTL circuit is a flip-flop made up by a pair of NOR gates, you could say it's a bit of memory! Why use a flip-flop? Well that's a good question which we still keep asking ourselves! In simple terms the flip-flop acts a memory for the last operation on that point, the memory is empty (0) then the point is working in one direction and the relay to de-powered. When the memory is full (1) then the point is working in the other direction and the relay has power to it. What this means is that we can have a push button method of setting the routes via a diode matrix and the system remembers what state each point should be in. NOR gates were used for the flip-flops as they were found to be least affected by the interference caused by the locos sparking as the inputs are normally held high. A manual override switch is provided for each point that gives you the flexibility to do operations that are not covered by the route setting. When there is more time available then this page will be updated with more bits on the wiring. last updated:12/01/06

ORWELL ST JOHNS
A Modern Image Layout in OO

The point work on the main lines and also the fiddle yard is all controlled by a form of route setting. Signals are currently manually set although it is hoped that they will be integrated into the route setting at some point. Loco control is down through conventional DC with cab control being deployed throughout, in addition to this, there are a number of relays that power sections of the track depending upon which route are set by the points.

Designing the system to run the route setting wasn't as simple as was first thought because potentially we had up to 11 point motors that could be thrown at the same time. To add to this we also wanted to integrate the signals into the route setting.

The initial problem was how to potentially throw 11 points at the same time, most CDU claim to throw 3 or 4 at most and the amount of power required to throw 11 would be quite great. We therefore adapted a method deployed by one of our members down at IRMA for reliable point operation as can be seen in figure 1 below, this originally only had one capacitor, but a second was added to help improve performance and help reduce a possible surge in current required from the power supply.

figure 1

When switch SW1 is thrown to activate PM2 capacitor C2 discharges and give a short but sharp bust of current to throw the point, power will pass-through PM2 until capacitor C1 is charged up. When SW1 is thrown to activate PM1, the opposite happens, C1 discharges and power will pass-through PM1 until capacitor C2 is charged up. Where a pair of facing points need to be thrown together the values of C1 & C2 are simply doubled to 2000uf with the point motors being wired in parallel.

For route setting to work switch SW1 is replaced by a relay that is capable of handling the current used by the point motors (or coils as the really are!) The relay itself is driven by the output of a TTL circuit, this TTL circuit is a flip-flop made up by a pair of NOR gates, you could say it's a bit of memory!

Why use a flip-flop? Well that's a good question which we still keep asking ourselves! In simple terms the flip-flop acts a memory for the last operation on that point, the memory is empty (0) then the point is working in one direction and the relay to de-powered. When the memory is full (1) then the point is working in the other direction and the relay has power to it. What this means is that we can have a push button method of setting the routes via a diode matrix and the system remembers what state each point should be in.
NOR gates were used for the flip-flops as they were found to be least affected by the interference caused by the locos sparking as the inputs are normally held high.

A manual override switch is provided for each point that gives you the flexibility to do operations that are not covered by the route setting.

When there is more time available then this page will be updated with more bits on the wiring.

last updated:12/01/06