A modern user interface based on a touch screen would be easy to implement using standard shields from the Arduino world. But given that the LGB locomotive to be controlled by the DMI is a (model) steam locomotive, a more “old fashion” look and feel with handles etc. was chosen.
The switch to the left is the Operational Mode selector. At the right top, you can see the Direction selector and below that, the Traction selector. The meter is indicating the speed of the train (in an arbitrary unit).
The meter and selectors are Russian surplus from the cold war, while the box is a modern ABS-box.
For the design of the DMI, see On-board Unit
- Microprocessor with Radio module (JeeNode)
- Power supply with battery
- Pilot indicators (LEDs)
There is not much to say about the circuit of the DMI. It is build around a micro controller of the Arduino type: JeeNode from JeeLabs This device has an integrated radio for communication with the OBU. The controller is reading the position of each selector via simple resistor networks. Indicator LEDs are driven directly by the controller and the analog meter is controlled by a PWM signal.
The figure to the right provides the circuit of the DMI. The microcontroller it self is not shown, only the connections to the controller. Arduino pin naming is used.
The power supply is a small DC-DC converter (TRACO: TRS 1-2433) providing 3.3V for the JeeNode. This allows the use of any battery in the range of 4.75 V to 36 V
The JeeNode has a pin-out that fits nicely with a standard PCB as shown in the next figure. The PCB holds the DC-DC converter and the few additional components. The resistor network for the selectors are mounted directly on the switches.