Team Digital SMD 8

Team Digital SMD8 Eight Output Switch Machine Driver

General: The SMD8 is a stationary decoder optimized to drive solenoid and stall motor switch machines. It derives all of its operating power from the track eliminating the need for a separate power source. A voltage doubler is used to charge a capacitive discharge circuit for operating solenoid switch machines. Stall motor machines are run from a separate internal power supply. Since the outputs are programmable as to switch machine type, stall motor and solenoid switch machines may be mixed together as desired.

The unit will operate up to 8 switch machines with each machine assigned a unique accessory address. The base address of the unit can be anywhere from 1 to 2041. The base address is the address of the first switch machine driver output, while the remaining driver outputs are the next seven sequential addresses. There are provisions for four fascia mount pushbutton switches for local control of the unit.

The feature of the SMD8 that makes it well worth considering is its ability to set up switch routes using the eight switches connected to it. It can be programmed with up to 16 separate switch routes, with each route composed of up to 8 switches and an associated switch position. Each route can be accessed by a single accessory address and a CLOSE or THROW command. This feature makes the unit especially useful for yard areas or other locations that require complex switch position set ups.

Each of the fascia switches can also be set to control a switch route. Again, each route can consist of up to eight switches. Since the fascia controlled routes need not be the same as any of the DCC (remote) controlled routes, the unit can control up to 20 different switch routings.

Connections: The SMD8 is very easy to connect. There is a single two terminal euro style terminal block for connection of power from the track or from a track feeder. The remainder of the connections are via RJ12 plugs and jacks. The unit has four RJ12 jacks used for switch machine connection. Each jack has the connections for two switch machines. If the machine is a solenoid type, then three connections are made: Common, Throw, and Close. If the machine is a stall motor type, then only two connections are made: Throw and Close.

A fifth RJ12 jack provides connections for the four fascia mounted manual switches. There is a common ground for all switches and then a separate control wire for each switch. These switches should be normally open momentary pushbuttons.

A second two terminal euro style terminal block provides a connecting point for the jumper wire required during programming operations.

Feedback: There is no provision for switch position feedback to the cab bus.

Programming: Programming is the most complex operation on the SMD8. The unit can only be programmed on the program track and is programmed by setting various values into the appropriate CV locations. There are a fair number of CV’s to be programmed, especially if you are using the routing feature, and it is easy to get confused. Further, there is no readback ability provided, so you can’t read what value is in a CV, you can only set it to the value you desire. For this reason, it is probably a good idea to go through the programming instructions and write down the CV and its associated value on a list before you start programming.

The programming mode is entered by installing a jumper on the programming connector and connecting the unit to the programming track. Set your system to program CV values. When the unit is in the programming mode, a red LED is on continously. Every time a CV value is successfully written, a green LED flashes momentarily.

To leave the programming mode, turn off the programming track power and remove the programming jumper. Reconnect the unit to the layout track or DCC feeder. The next time power comes on, the unit will operate in its normal switch control mode.

During programming, you must program CV1 and CV9. These locations establish the base address of the SMD8. You must also program each of eight CV’s (one for each output) to establish whether the output is driving a solenoid (three wire CD drive) or a stall motor (two wire reversing drive). If you are only going to address switch machines individually, then these ten CV values are all that you need to do. Route programming gets a little more complex.

First, you must program a route address. This is basically an alias address that looks to the DCC system as if it were a single switch, but in reality it is the address of an entire route. When you access the route address, a Throw command from your cab will cause one route to activate, while a Close command from the cab will activate a different route. Thus, once you establish the base address, the next four addresses combined with Throw and Close commands provide access to eight different routes. CV25 and CV26 are set to base addresses that provide access to a total of sixteen different routes.

Next, for each route, you must tell the SMD8 which switches are in that route and what the position of each switch is for the desired route. Thus, for each of the 16 remote routes and 4 manual routes there are two CV values to program (total of up to 40 CV values). If you don’t need all 20 routes, it is OK to leave some of the CV’s at their default value of 0, which disables switch selection and position for the associated route.

Manual: The manual is a single page, printed double sided and folded. It does contain all of the information you need to operate the SMD8, but you will probably need to read through several times to figure out all of the details. The discussion above will hopefully help you work your way through the manual the first time.

Performance: In a word: EXCELLENT! I measured 25.8 volts on the capacitive discharge storage capacitor. Not surprisingly, this resulted in very solid performance of the NJI switch machines that I used in my test. These are large and include auxillary contacts, so take a fair amount of energy to operate. The SMD8 had NO problem operating these units. My guess is that if the SMD8 can operate these units, it will have no trouble with anything on your layout.

I was a little disappointed with the performance on stall motor switch machines. The unit was competent, but the stall motors were a little sluggish. I measured 9.1 run volts at 3.0mA and 4.9 stall volts at 7.1mA. The run voltage is below that found in some other accessory decoders, but does provide acceptable stall motor performance.

The unit will run lamps and LED’s in the stall motor configuration, but an external power source is required for this. For this reason, other decoders are probably more appropriate if you are driving lights.

Similarly, there is no provision to provide motor on/off control, so my accessory motor was not compatible.

As part of my test, I set up a four switch route with two NJI solenoid switch machines and two Tortoise™ stall motor switch machines. The route feature worked very nicely. Since the unit uses a CD drive for the solenoid machines, it needs to recharge after each solenoid throw. The SMD8 has built in sequencing to allow the CD system to recharge after each solenoid operation. The delay between throws is about 2 seconds. Thus, when I triggered a route, NJI machine 1 would operate, followed by a 2 second wait, then NJI machine 2 would operate and then the two Tortoise™ machines would operate. The whole sequence triggered by a single accessory Throw or Close command. Very nice!