Tapiola Parish Model Railway Club

Computerized Signal Box (Power Box) at Helsinki club

At Tapiola a different approach was "invented": All cabs had their own relay banks and each of them were divided into "odd" and "even" blocks of relays.

If the loco is on "odd" section of track, no power is travelling through the "even" relays, and they can change state. As the train enters to "even" section, no power travels through the "odd" relays, and they can change state. A loco will only need two sections to be powered at one time, provided we know the direction the the loco is travelling, or if lineside signals are so set that the loco has no way of travelling to unpowered section.

An example:

As the loco was under control of cab A and was on an even block, the odd bank of cab A's relays could connect the power to the next or previous block. This way only two blocks could be connected to a same cab, but that is enough!

The layout had 13 blocks and 3 cabs and only needed 19 relays (3 cabs: 8 even and 8 odd blocks (3 relays each). The one extra relay took care of handling the power routing while going from block 13 (odd) to block 1 (odd).

NB: No saving in relay count will be gained, if the number of blocks and/or controllers/cabs is small. The pictures show a situation were the excact number of relays needed is the same, but if the system is larger, the relay count comes down nicely.

Picture of the inside of the CTC-panel, the relays are in the middle

Forwarding

If a train is standing in a station with power applied. The computer knows that this is to be connected to engineer A. If the points were thrown, the train becomes isolated and the detector looses the train. Now the computer switches off the power, but puts the cab code in memory if the engine becomes detectable again.

Train leaving the station

If we are to forward this train from the station, we must first set the points to that siding. The detector notices the train and computer switches power to the rotary section. If we then give the train a permission to proceed say, from section 6 to section 7, the power of cab A is applied to section 6 (as detector picked up the loco) and to section 7 if starter signal is cleared.

The CTC-panel showing a train about to depart from siding (Yellow LED next to turnout detotes that it's thown, red LED in the track diagram denotes that the train detector has sensed the train, and green LED inside signal symbol is lit to show that the train may proceed. the black buttons top right are group buttons used in conjunction with the switch immediately below the station area. If a train is to be forwarded, the switch below station area is thrown to the direction of intended travel and black group button ("Kulkutien varmistus") "create route" is pressed. if the route need s to be canselled, the group buttom "kulkutien hätäpurku" ("emergency delete route") is pressed. In case the train crew needs to do shunting within station area the group buttons "paikallisluvan anto ("grant local control") and "paikallisluvan palutus" ("delete local control") will be used. This will provide power to both ends of the station area blocks irrespective of train detectors.

The same situation on screen: due to lack of space the rotary sections are coded with letters instead of numbers. The line (with text "Twin-T") has a star where a train is detected. immediately above the star there are arrows at blocks 6, 7 and 8 (f, g and h) denoting that the computer is giving permission for the train to proceed to the right from these sections. The row marked with text "Kytk!" ("conn!") denotes which cab is connected to this section. We see that the cab/controller 1 (or A) is connected to sections 6 and 7 (f and g). The row marked "Muisti" ("Memory") displays the throttle numbers that are taken in to memory in case two locos occupy same block (but the one in memory has been made dead by throwing points!). The kind of tunnel shown on screen at block 3 (c) means that the turnouts are so set, that a train travelling from block 2 (b) will travel directly to block 4 (d), and not through the block 3, which is the goods yard. The numbers with arrows above the track line are denoting which of the computer's function keys would create route. By pressing the space bar one could toggle between four group buttons, and the text at the top of the screen showed which of the group buttons was activated (this was used before the control panel got the buttons). the area marked as "releet" (relays) displayed the status of the four output ports. the state was displayed in decimal and binary form. The "Kierr.aika" ("loop time") shows the real time loop time (this version has quite a lot of code in assembler, the plain basic version had reatime loop times well above 2 seconds!

As the train proceeds it will appear in section 7 and later dissappear from section 6. The computer knows that trains don't dissapear, but move from one section to another, so if due to bad contact the train should dissappear while about to move to section 7 no false actions will be made. Only as the train is completely within section 7 will the section 6 be released. If the section 6 would be the destination of the train, the dissapearing of the train is considered as the train being isolated by throwing the points -- the section will be de-energised and the cab code will be put into section 6 memory. If this was an intermediate section and not the destination, as is now the case the dissappearance of the train will not de-energize the secton.

Train meet

If another train is to enter the station occupied by a train, the standing train must be made dead by throwing the turnouts to a free siding. Now the cab number of the standing train dissappearing from detection is put into memory and the section may now be assigned to the cab of the approaching train. If this train is accidentally loosing contact, the cab cannot be put into memory as there is already another cab code there!

Only after the train has completely left the rotary section that the standing loco occupies, may we re-energize the standin loco by throwing the points. Now the loco will get the cab assignded by the code in memory.

Passing a train

13 train detectors were needed, and they were connected so that, while using power routing turnouts, they lost sight of the train as the points made the track or section dead.

But as the computer knew that the points were thrown it thus knew where the loco was. The detectors were a sort of mixed design of diode version of Twin-T and Mudies detector (described in 1970's in MR). (Again, I throught that Dr Chubb's design of Optimized detector was not optimized moneywise, I'd rather have four detectors with the price (and component count) of one of his ;).

The actual detection part consisted of anti-parallel diodes and antiparallel transistor base-emitter junctions. The collectors were tied together and formed a open collector output with no delay. A 33 nF capacitor was need to smoothen out erroros. This diode+transistor unit was assembled on a thumbnail size vero board, inserted into plastic film container and connected underneath the layout. the open collector lines were taken to the control panel for delay and amplification. This made the heavy duty wiring shorter too.

The schematic of delay/amplification unit and picture of the quad delay/amplifier

The amplification consisted of 1/4 LM324 op-amp, 1 uF / 3.3 Mohm three seconds off delay and instant on and sensitivity trimmer.

Post Mortem

With PC you could get all the info through a Centronics port, and at around 10 dollars a piece it is not a great investment even though you would blow one. Unfortunately todays computers running under Windows have no longer direct connection to LPT port, so one must either make a bootable diskette and load old fashioned DOS software there with the operating system, or resort to commercial software, but those are nicely tied to only commercial hardware so the DIY programmers are really having hard times!