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Part 5: the throttles & control panel In this concluding article in the series on the Proto­power 16 Command Control system we describe the wiring of the handheld throttles and the control panel. The handheld throttles may be wired with or without inertia and may have provision for “double-heading”. Design by BARRY GRIEGER The circuit of the basic handheld throttle is very simple and is shown in Fig.1 on the facing page. It uses a single-pole double-throw (SPDT) switch (S1), a 10kΩ linear potentiometer and requires just four wire connections back to the control panel. Three of those connections come, via the control panel, from the terminal strip on the encoder board: Forward (+1.2V), Reverse (+8.8V) and Stop (+5V). The fourth wire is the Output (wiper) connection from the 10kΩ linear potentiometer. The Forward and Reverse wires go to the outside terminals of the SPDT switch. Our prototype handheld throttles used minia­ture slide switches but they could just as easily have been miniature toggle or rocker switches instead. The moving contact of the SPDT switch is connected to one side of the 10kΩ poten­tiometer. The prototype throttles were wired up in the smallest prac­tical plastic boxes using 6-core flexible cable. Don’t use telephone cable here by the way because each of the six wires is solid core and with the amount of flexing that can be expected on throttle cables, you can expect wire breakages. Any cable you use to wire up the handheld throttles must have multi-strand cores, to allow it to flex. You can use 4 or 6-core cable, shielded or unshielded, just as long as it can take a lot of flexing. Ignore this point and Run your model railway with Command 82  Silicon Chip you will be giving yourself a lot of headaches in the future. Make the throttle cables as long as seems necessary but typically, a length of about 1.5 metres or so will probably be adequate; any longer and it will be prone to tangling or tripping you up. Terminate the free end of the cable in a 5-pin DIN plug. You can use whatever method of termination to the DIN plug you like but it must be consistent for all plugs and sockets. We suggest using pins 1 & 3 for the Forward and Reverse connections, pin 2 for the Stop connection and pin 4 for the output connection. The number of throttles you will need depends on the number of people who are expected to operate the layout at any one time. Typically, we expect that most layouts will need three or four handheld throttles but you could have up to 16, one for each channel on the system. In practice though, we think that having any more than about six people operating locomotives on the layout at one time would be unwieldy. Inertia throttle While the simple throttle of Fig.1 will suffice for many users, some readers will want a handheld throttle with built-in inertia, or momentum, as it is sometimes referred to in model railway magazines. In effect, the inertia circuit simulates the enormous mass of a real train and therefore only allows the train to accelerate or decelerate very gradually. Fortunately, inertia can be incorporated very simply with the addition of two capacitors and a resistor, as shown in the circuit of Fig.2. As you can see, the voltage from the potentio­meter’s wiper connection is fed through a 10kΩ resistor to a pair of 470µF electrolytic capacitors con- nected back to back. This gives a resultant capacitance of 235µF and this provides a delay whenever the throttle setting is increased or decreased. The two electrolytic capacitors are connected back to back to provide a bipolar capacitor, which is necessary because the forward/reverse switch can cause the voltage polarity across the composite capacitor to be either positive or negative. By the way, if you find that the amount of inertia provided is not enough, you can increase it by doubling both capacitors, from 470µF to 1000µF. Alternatively, you can get a similar result by increasing the 10kΩ resistor to 22kΩ. In other respects the wiring of the inertia throttle is exactly the same as for the simple throttle of Fig.1. Switchable inertia & braking While inertia adds realism to operation, it can be a draw­back in shunting manoeuvres so it is worth having a switch to switch the inertia in or out. The circuit to do this is shown in Fig.3 and the inertia switch is S2. Note the 470kΩ resistor across S2. This is to keep the inertia capacitor charged to the current throttle setting so that if you inadvertently switch inertia in while running, there is less of a change to the train velocity. And yes, we reckon that some people will want locomotive braking as well and this is just a further refinement on the circuit – see Fig.4. Here, we switch a 2.2kΩ resistor across the back-to-back 470µF capacitors using a pushbutton switch, S3. Each time the pushbutton is pressed, the capacitors are discharged via the 2.2kΩ resistor and the train comes to a stop. The value of 2.2kΩ is chosen as a compromise between real­ism and safety. In reality, trains just cannot Fig.1: this is the basic throttle circuit providing just speed (VR1) and direction (S1). Fig.2: this throttle incorporates inertia with the two back-toback electrolytic capacitors. come to a rapid stop but in model practice, when you apply the brake you may want the train to come to a stop in a short distance to avoid a colli­ sion or over-running points, etc. Naturally, you can increase the severity of braking by reducing the value of the 2.2kΩ resistor. Note that if you apply the brake and leave the throttle setting unchanged, the loco will not come to a full stop. In effect, it would be like applying the brakes on a real locomotive but still keeping the engine going – not very realistic! So for the train to come to a full stop, you need to apply the brake and reduce the throttle setting to zero. In normal operation, if the greatest realism is to be achieved, we expect that the brake will only be used in an emer­gency stop. At other times, the Control June 1998  83 Fig.3: adding switch S2 and a 470kΩ resistor to Fig.2 allows the inertia to be switched out which can be handy when you are doing shunting manoeuvres. train will be accelerated or decelerated to a stop with the inertia circuit switched in. Double-heading throttle Double-heading of locomotives pre­sents a problem for a Command Control system since effectively you need a handheld throttle for each locomotive. That becomes a little tricky, as you might imagine trying to juggle two controls, and is doubly inconvenient (pun intended) if you want one of the loco­motives to run in reverse. How do you do it? Fortunately, it is quite easy and all you need is a “double-heading” throttle which uses Fig.4: switch S3 adds braking. When S3 is pressed it discharges the inertia capacitors but the throttle (VR1) should be wound back to allow the locomotive to come to a full stop. a dual-ganged 10kΩ linear potentio­ meter. This throttle circuit is shown in Fig.5. You will notice that it is essentially a doubled-up version of Fig.1 but the slide switch reverses the voltage to the second section of the pot, VR1b. Essentially, we send a forward and reverse command to the locos simultaneously, from a single throttle. Why reverse the loco? Old hands at railway modelling will probably be puzzled by the need to reverse one locomotive of the pair when double-heading, so it needs some explanation. First, we should comment This throttle has been wired for double heading a pair of loco­motives and uses the circuit of Fig.5. 84  Silicon Chip that if you are double heading you can run both locomotives head-to-tail, in which case both will be running in the same direction and there is no reason to reverse one of the locos. But if you want to run the pair of locomotives “tail to tail” as is often done in “full size” trains, then the second locomotive of the pair must run in reverse and it must receive a throttle signal to tell it to do so. This is where the old hands may be puzzled because they will be aware that if you pick up a model locomotive off the track, swap it end for end and then put it down on the track again, it will continue to run in the same direction as before. That is because, in a conventionally wired layout, the track polarity determines the direction of motion; swap the track polarity and the loco will reverse. However, in a Command Control system the track polarity is con­stant and the track voltage does not vary either. The only way that the locomotive can change direction is for it to get an appropriate throttle forward/ reverse signal. So if you pick up a locomotive in a Command Control system, swap it end for end and then place it down on the track again, it will head off in the opposite direction! So now you should be clear as to why a “double-heading” throttle needs a dual-ganged pot and is wired as shown in Fig.5. Note that the forward/reverse switch is now a double-pole type (ie, DPDT) but most slide switches tend to be this variety anyway. When you are wiring the 5-pin DIN plugs for the This prototype control panel has eight DIN sockets to let eight single or double-heading handheld throttles to be used simultaneously. The row of RCA sockets along the bottom corre­sponds to the 16 channels of the system. Associated with each DIN socket are two RCA sockets wired to pins 4 & 5. The DIN sockets are connected via patch cords to the wanted RCA input channel. double-heading handheld throttle, we suggest an extension of the conven­ tion outlined above: Pin 1, Forward; Pin 3, Reverse; Pin 2, Stop; Pin 4, Forward Output (lead loco) and Pin 5, Reverse Output (trailing loco). Naturally, the refinements of inertia and braking can be added to the circuit of Fig.5 but the wiring does tend to become a little busy. The photos of the wiring in one of the handheld prototype throttles actually shows the “double heading” circuit used in Fig.5. Finally, if you are going to run a permanent double-heading locomotive lash-up, then the easiest way is to set both locomo­tive decoders to the same channel and then you can use a simple throttle as per Fig.1 or its variants. Note that in any double-heading locomotive lash-up, both locos should ideally be the same and have the same motors, gearing and so on, so that their speeds will always be matched for any given throttle setting. Control panel The above photo shows a blue con­ trol panel with two handheld throttles plugged in. The prototype control panel has eight DIN sockets to let eight single or dou­ ble-heading handheld throttles to be used simultaneously. If you want more, the panel will have to be extended or the DIN sockets squash­ed more closely together. Also arrayed on the control panel is a large number of RCA sockets. Along the bottom of the panel is a row of 16 RCA sockets and these correspond to the 16 channels of the Protopower 16 Command Control system. Each one of these RCA sockets is wired to the 16-way cable connecting to the encoder board. Then you will notice that there are two RCA sockets asso­ciated with each Fig.5: a dual-ganged potentio­meter (VR1a/VR1b) and a DPDT switch (S1a/S1b) allow two locos to be controlled in a double-heading lash-up. of the eight DIN sockets. Each pair of RCA sockets is wired to pins 4 & 5 of the associated DIN socket so they represent the throttle outputs for the handheld control. Now, here is the big question: how is the connection made between each of the RCA throttle outputs and the 16 RCA throttle inputs to the encoder board? The answer is quite simple: you need RCA to RCA plug patch cords. So the way each handheld throttle is assigned to a particu­ lar channel is merely to connect a patch cord between the throt­tle output and the wanted input channel. Simple! If you want to run eight throttles and have them all with the possibility of double-heading, then you will need at least 16 RCA to RCA patch cords and they will need to be long enough to reach from one end of the control panel to the other, in order to provide for any throttle to go to any channel. Or you could make things a little tidier by making some patch cords long and some short although that will probably limit your flexibility. As well as the 16-way ribbon cable to the encoder PC board, the control panel will need three wires going back from the DIN sockets to the Forward (+1.2V), Reverse (+8.8V) and Stop (+5V) connections on the encoder board. Since each layout will have its own features, we have not provided a wiring diagram. Depending on your preferences, the control panel could be combined with the other control gear for your layout – lighting, points switching and so on. Have fun! SC June 1998  85