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DCC Engine Code Tester

Engine Code Tester

This project is very simple to build. Totally 15 discrete components and an IC are soldered together on a piece of experimental board (i.e. Veroboard) and you get this module to operate.

The DIL selector is electrically a 4 times SPDT which gives the input pins 1-4 each a choice of signal ground ( = logic LOW), or open, or IC-plus (= logic HI). That corresponds to the selector of the T 80 and more theoretical explanations may be found in that section of the book. There is also a complete code guide in the book should you have lost the one that came with the Marklin central control unit. Please note that in this project the pin #5 of IC1 is grounded.

To get the right voltage level for the module there is a zener diode D1 parallel to a capacitor C1. Additional voltage drop is achieved through D2 (also rectifying the power) and R4. In order to get correct timing for the IC there are two oscillators R2-C3 and R3-C2. More detailed theory on how to calculate their values is found at the end of the book in the components section.

Finally to three of the outputs there are LED’s connected and current limiting resistors in series with them.

How to use the tester Start with power off and connect each clip to appropriate rail (red to center rail and brown to one of the outer rails on the track).

Next power up the system to be tested. Now is a good time to select the correct code both on the tester and on the central control / control 80f. If power is correctly distributed to the track (red light on central unit is lit) and you have matching codes the orange LED should be ON. You should now be able to rotate the speed knob and get various light combinations on the green and red LED’s. A reverse command by the knob should produce a red light, and most speedsteps will be indicated.

By this “signature” of light you will get a feedback from track that a matching address code is distributed and that various data commands also get through. So it is likely that the code and power is correct. If nothing shows on the display do try the OFF- Light key on the central unit. If that still doesn’t help then the code is simply not present for the tester to read.


Parts List – Engine Code Tester

IC1 MC 145027 Motorola chip
D1 8.2 V Zener Diode 0.4 W
D2 1N4001 Diode
D3 5 mm red LED
D4 5 mm green LED
D5 5 mm orange LED
C1 10V / 16V electrolythic Cap
C2 2.2 nF Capacitor
C3 4.7 nF Capacitor
R1-R2 270 kOmega 1/8 W Resistor
R3 12 kOmega 1/8 W Resistor
R4 2.7 kOmega 1/8 W Resistor
R5 470 Omega 1/8 W Resistor
R6 150 Omega 1/8 W Resistor
ECS Selector DIL-switch
Project Credit:      Rutger Friberg

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