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F1-F4 Functions Tester

As remarked earlier there is in the book an extensive tester T80 for the Marklin digital system in H0. It is one of the major projects and it is supposed to be assembled on a premade PCB. This project , which comes additional to the DIY-projects in the book has unique testing capability in that it can extract the extra functions signals from the engine code and indicate those in a simple manner. So it is a complement to the T80 and very simple to build. Totally 16 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 connected to IC-plus.

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 four of the outputs there are LED’s connected and two 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 engine 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, you should now be able use the F1 through F4 function keys on the control 80f and get appropriate LED on the tester to be lit. Any combination should be possible to lite up.

By this “signature” of light you will get a feedback from track that a matching address code is distributed and that wanted data commands also get through. So it is likely that the code and power is correct. If nothing shows on the display do check that the transmitted engine code (selected via the keys 0-9 on control 80f-unit) is the same as the received code (selected via the DIL-switch on the tester). If that still doesn’t help then the code is simply not present for the tester to read.

Parts List – Functions Tester

IC1 MC 145027 Motorola chip
D1 8.2 V Zener Diode 0.4 W
D2 1N4001 Diode
D3-D6 5 mm red 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-R6 150 Omega 1/8 W Resistor
ECS Selector DIL-switch

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