Team Digital SMD2

Team Digital SMD2 (buy)

General

The Team Digital SMD2 is designed as a two-output switch machine decoder. It will work with twin coil and with stall motor type switch machines, including controlling one of each type with a single SMD2 decoder. The unit has a single two-wire input for connection to the DCC bus and a standard 6-pin RJ12 style output connector for switch machine interconnection. The SMD2 measures 2.75 X 1.63 X 0.97 inches and does not require any additional power source other than the DCC input.

The outputs of the SDM2 can be independently programmed to any one of four types. The first configuration is designed to operate a twin coil switch machine, while the second type is designed to operate stall motor switch machines such as the Tortoise™. Type three is the same as for the stall motor machine, but it is only on for 5 seconds. This configuration is designed for situations were the unit controlled does not need continuous power to maintain a position and is designed to lower current draw by the layout. The last output type is manual. In this configuration, the output will simply respond to the cab inputs. The twin coil output is queued to allow the capacitive discharge driver time to recharge. The switches operate in sequence with a pause between operations. The remaining outputs are not queued since they require no charging time. There is no provision for direct manual operation of the SMD2.

The SMD2 can be set with the addresses of the two outputs either sequential or random. In addition, the SMD2 supports combination addresses. Since the SMD2 has two outputs, the controlled switches can have a total of four configurations: close/close, close/open. open/close, and open/open. Each of these switch configurations can be assigned a separate address. Combination addresses is a handy feature for controlling, for example, a double slip switch. This switch has two switch motors and four possible routes through the switch. Each route can have its own address relieving you of the task of figuring which switch to set which way for which route.

The SMD2 provides an option to remember the switch state when the layout power is turned off. With this option enabled, the SMD2 powers up when the layout is turned on and returns all switches to the position that was present when power was turned off.

Feedback

There is no provision for cab bus feedback from the SMD2.

Programming

The SMD2 has two programming modes. The first is called “smart” programming. In this mode, the included programming jumper is installed and the unit is turned on while connected to the main DCC. A switch command is issued to the address that you want assigned to the first output. Turn power off, and remove the program jumper. The SMD2 has the first output at the address issued, and the second output assigned to the next sequential address. You cannot program output type, random addresses, or combination addresses in this mode.

All other programming of the SMD2 is done on the programming track. The SMD2 has 15 CV locations that can be programmed for various options. I found the CV programming to be somewhat tedious because the SMD2 does not provide CV read back acknowledge. This means that you constantly have to wait for the CV read to time out and/or get a message saying that the CV cannot be read. The CV values are correctly programmed; it just takes some time.

An important point to remember is that the programming jumper must be installed to program the device whether on the main or on the programming track. It is easy to forget while using the program track, and you will have to redo all of your CV entries. The SMD2 will appear to program, but it will not take the new values (yes, I did “program” it without the jumper).

When programming your SMD2, it must be programmed before you install it onto your layout. The best approach is to figure out the configuration that you want, and then make a list of all of the affected CV’s with the desired value. Then put the unit on the programming track, install the programming jumper, and set all of the CV’s to the desired state. Now, remove the unit from the programming track, remove the programming jumper, and test that it works as you expected. If all looks correct, then install it on the layout.

Manual

The four-page manual is clearly written. It devotes a section to each set of options and clearly discusses how to set each one up and how to accomplish the required programming. There are simple, clear schematics showing how to connect the SMD2 to the layout and how to connect a solenoid and stall motor style switch machine. Team Digital also has a web site with further application information.

Performance

The SMD2 performed extremely well with both twin coil and stall motor switch machines. For twin coil machines, the SMD2 uses a capacitive discharge system to power the solenoid. In this approach, a capacitor is charge over a relatively long time and then rapidly discharged through the coil. This way, very large coil currents can be produced for solid operation without drawing huge currents from the layout booster. As an added feature, the SMD2 uses a voltage doubler to charge their output capacitor to 26 volts. With the Nick & Jack International twin coil switch machine as a test load, the instantaneous output is in the range of 13 amperes. This current pulse really moves the NJI machine along. There is no hesitation, and the solenoid moves with a solid snap. Since the NJI twin coil switch machine is my toughest load, there is no problem operating the lower power Peco switch solenoid or other similar devices. One of the benefits of capacitive discharge technology is that very large currents are used to operate the switch machine effectively, but these high currents are only present for a short time until the capacitor is discharged. Once discharge, there is very little current available. This feature makes it almost impossible to burn out a switch motor while allowing proper operation at very high currents.

The capacitor discharge technique is sort of like flushing a toilet, once the tank is drained, you must wait for it to fill up again. For this reason, the twin coil output configuration is queued. This means that if two switch commands are issued very close together, the first one will be executed while the second is held (queued). After the first operation, the capacitive discharge circuit is recharged, and then the second switch command is released for action. I timed approximately 3 seconds between switch operation commands in this mode. The other operating modes do not require queuing, and simultaneous operation of switches is possible (including if one of them is a twin coil machine).

Operation of the SMD2 with a stall motor switch machine achieved very acceptable results. I measured 10.8 volts operating and 7.19 volts stalled on the output. These values are sufficient to properly operate a stall motor machine. As the numbers indicate, the Tortoise™ test load ran well with good running torque and very good holding torque.

Recommendations

The SMD2 is an excellent choice for either twin coil switch machines or stall motor switch machines. It is a particularly good choice if you have some of each and need to mix and match output by output.