This page shows schematics and diagrams for a MiniDCC© system that was built for my personal use.
The home page for the MiniDCC© system can be found at the following link. Questions about the operation of the MiniDCC© controller should be sent to the site in the following link.
A 13.8 Volt / 4 Amp, battery eliminator type of power supply was used as it has all of the desired safety features already built in. The regulated output voltage is a bonus. When compared to building a power supply, this was a economical option and the supply can be used for other purposes when not in layout service.
The 1N5400 - "Crowbar Diode" protects the system by causing the 4 amp fuse to blow if the power supply is accidentally connected with its polarity reversed.
The following schematics and photographs show the As-Built version of my MiniDCC© system. These are provided for information only.
My MiniDCC© system has had many modifications from the original system. Some of these changes are described in the following notes.
A circuit (Q1/Q2) has been added to the controller that mimics the Emergency Stop button (S1) being pushed if the booster shuts down due to a DCC Signal failure or an Over-current trip occurs.
Switch S3A has been placed in series with the MENU SELECT switch (S2). This was done so that the EMERGENCY STOP button could not be accidently overridden if the MENU SELECT button was pushed first in an emergency stop situation. A better solution would be to move the MENU SELECT button away from the EMERGENCY STOP button.
Switch S3B disables the Walkaround Remote unit when the MENU SELECT push button is active. This was done so that the buttons of the remote can not accidentally make changes when the controller is in the programming and set-up modes.
Switch S4 allows the Walkaround Remote unit to control engines 3 or 4 depending on its position.
The CD 4016 - Quad Bilateral Switch is used as an adapter that mimics the operations of the buttons of the key pad when five volts is applied to one of its inputs.
As part of the Walkaround Remote system an 'AND' gate (Q3) was added to the CD4016 adapter circuit. The net result being that if both the ACCELERATE and BRAKE buttons are pressed at the same time the EMERGENCY STOP signal is sent to the controller.
There is a bug in this method however; If the ACCELERATE and BRAKE buttons are pressed at exactly the same time the EMERGENCY STOP is not activated. If they are pressed a fraction of a second apart the method works correctly.
The schematic shows a single - 33 Ohm / 1 Watt resistor before of the voltage regulator, in the as-built circuit two - 68 Ohm / 1/2 Watt resistors were used as seen in the photo of the 5 Volt Regulator circuit board.
The following photographs are external and internal views of the As-Built controller housing. The housing is 19.5cm. by 11cm.
The Walkaround Remote unit is connected to the system by a six pin DIN type plug and jack. Five conductors are used for the remote but the sixth conductor, the circuit common, allows for a possible radio controlled remote in the future.
The MiniDCC© system controller IC and its circuitboard are at the bottom of the box. They are held in place by two sections of styrene 'I' beam.
The black bands around the groups of wire are small pieces of heat shrinkable tubing. In most cases the tubing has not been shrunk.
The following schematic is for the booster that was built for my MiniDCC® System. Designed around an LMD 18200 H-Bridge. The circuit includes signal failure detector and over current protection that will remove power to the tracks should either activate.
The signal detector will automatically clear itself but the over-current detector must be manually reset.
As Built 3Amp DCC Booster Circuit schematic
It is unlikely that the 'Thermal Flag' LED would ever go on as the heatsink that the LM18200 is clipped to is much too large for the load expected.
The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.
If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.
Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.
12 March, 2011