Team Digital, LLC

SMD2/SMD8 - Switch Machine Driver Application Information
Solenoid Type Switch Machines:
The following switch machines have been tested:
  Atlas HO snap
  NJI
  Peco PL-10 "black"
  Rix Twin Coil
  Kato N unitrack - requires two external resistors

All the machines were tested with a Digitrax DB150 Command Station set to the appropriate scale. The Rix twin coil machine requires tension on the swing arm to keep the internal weight from bouncing off its end stop when the pulse of power is applied. Operating the machine without tension on the arm gives the impression that it is not working correctly.

The Kato unitrack electric turnout is a special case since it only has two electrical connections as compared to three for the others. The SMD2/SMD8 provides power on the common connection, so two resistors are required from the common to power the machine. Figure 1 below shows how the resistors are electrically connected. Warning: the SMD2/SMD8 output configuration must be set to solenoid type operation for proper operation. To see detailed information on adding resistors to the SMD2 go to the SMD2/Kato page.

Most solenoid type machines require a large pulse of power. The design intent of the  SMD2/SMD8 was to have enough power to be able to activate "snap" any HO/N scale solenoid type switch machine even when they were some what "sluggish".

There are several factors that can contribute to poor "sluggish" performance. A few include electrical connections at the driver and the machine, size and length of wire used for connection and mechanical linkage from machine to switch. If you are having problems check these areas.

The SMD2/SMD8 uses RJ-12 modular connectors because of space requirements and because modular components are readily available. Modular wire (flat phone wire) is available in 28 and 26 gauge sizes. Size 28 is not recommended . A better choice is to used 26 gauge. The best choice, although a little more difficult to install the modular connector, is the round 3 pair (six wires) 24 gauge phone wire. If you use the 26 gauge wire try to keep the wire length to each switch machine to under 12 feet. With 24 gauge you should stay under 18 feet.

Route Features:
The internal route feature of the SMD8 is well suited for controlling yard switching. With a single switch command up to eight switches can be controlled at a time. Up to 16 individual routes can be configured, so there is a wide range of combinations available. See figure 2 for an example of route usage in a yard.

The SMD2/SMD8 work very well where 3 point and double slip switches are used. The internal route feature allows for a single switch command to position these types of switches.
Local Input:
The SMD2 does not have any dedicated inputs for local control. However, if you really need one, the programming (PGM) pin can be used as an input for local control. If the PGM pin is grounded when power is applied, the SMD2 will be in program mode. If the PGM pin is NOT grounded when power is applied, the SMD2 will be in normal operation and the PGM pin then can be used for an input. CV28 is used to enable and configure what action the SMD2 outputs take when the PGM pin is grounded in normal operation. Following is a table showing CV28 values and action.
value

 0
 1
 2
 3
 4

 17
 18
 19
action

no action
output 1 throw
output 1 close
output 2 close
output 2 throw

output 1 toggle
output 2 toggle
both outputs toggle
value

 5
 6
 7
 8
action

both outputs close
both outputs throw
output 1 close/output 2 throw
output 2 close/output 1 throw

SMD8 Known Problems:
2/17/03:
Changing output configuration from stall type to solenoid type. If any SMD8 output has been configured for a stall type machine and operated, then subsequently reprogrammed for a solenoid type, that output does not function properly.  If you are not using stall type machines or not planning on changing output configurations, you will not experience this problem and the SMD8 will operation properly.

SMD8s with this problem can be identified by two silver marks on the integrated circuit (IC). Replacement units are available by contacting us .

2/5/04:
NCE specific.  The Powerhouse Pro attempts to read each CV before programming that CV. Sometimes during the read back attempt the SMD8 stops responding to programming.

Solution:
With the SMD8 disconnected from the programming track, start programming like you normally would.
When the Procab can not read the CV value it says "CAN NOT READ CV"
1. Press the "ENTER" key
2. Type in the CV value.
3. Connect the SMD8 to the programming track. (the red LED will go on)
4. Press the "ENTER" key.   (the green LED will flash)
5. Disconnect the SMD8 from the programming track. (the red LED will go out)
Repeat this sequence each time you program a CV.

SMD8s with this problem can be identified by three or less (version 3 or earlier)  silver marks on the integrated circuit (IC).
smd8 application diag