From SPCoast
Jump to: navigation, search

A simple bench test board for Chubb's DCC-OD and MRCS' cpOD detectors.


This board is designed to be a bench test unit for Chubb's DCCOD style detectors. A board is inserted into the test pins and the three buttons are pressed in sequence while observing the "detected" LED. A "good" board will light up with both the "low" and "normal" button presses, but not the "high" one. The DCCOD sensitivity can be adjusted in the jig to give the desired behavior.

A local test track can be optionally connected that enables the testing of specific locomotives and rolling stock simply by placing them on the track.

The values for R1, R2 and R3 should be chosen for the layout and locomotives in use - N-scale's small highly efficient motors will draw less current than a O- or G-scale, and will require greater sensitivity. Your wheelsets may provide 10K or 100K resistors, which should also inform your choices. The values below are astarting point; feel free to experiment. There is nothing wrong with choosing 100K as "normal" and 150K as "too high" as long as your choice of "turns" thru the DCCOD's pulse transformer can provide the detection. Start with "normal" matching your wheelset/rolling stock resistors, "low" being half of that, and high being 2x to 10x of normal...

Validate that your DCCOD can actually detect your chosen values by adjusting its potentiometer to its mose sensitive position and observing that the detected LED lights when the buttons are pressed.


  • Plug a DCCOD board to the DetectorTester.
  • Connect to a 12v DC regulated power supply.
  • Connect the output of a DCC booster to the DCC connector
  • Press one of the pushbuttons to place a detectable load resistance across the "track" for the detector to see
    • Sensitivity test values (choose to match your givens and druthers)
    • 5K resistance (~3mA)
    • 10K resistance (~1.5mA)
    • 100K resistance (~0.15mA)
    • 150K resistance (~0.1mA)

Use the following table to diagnose/adjust based on the whether the detection LED lights when the following buttons are pressed:

OFF OFF OFF Nothing lights, missing DCCOD, no DCC power, no DC power, poorly chosen R1,R2 and R3
OFF OFF ON Bad detector test board - check solder connections
OFF ON OFF Bad detector test board - check solder connections
OFF ON ON Bad detector board - check solder connections
ON OFF OFF this DCCOD will have problems detecting a typical car resistance. Adjust DCCOD until NORMAL lights, also
ON OFF ON Bad detector test board - check solder connections
ON ON OFF this DCCOD is properly adjusted
ON ON ON this DCCOD is potentially overly sensitive, and may false trigger. Lower the DCCOD sensitivity until this just extinguishes


Make the resistors pads 0.400 across. The standard red triangular benders only go down to 0.400 so bending to 0.300 requires doing it manually. Made the 100uF a 3.5x10 package to match what is in stock... Fixed silk screen TRACK and DCC Boxed the LOW and NORMAL buttons to indicate that they both chould trigger, and the HIGH one should not

Project Files

V2: external DCC source connector as well as external test track for testing rolling stock

Project Files

V1: No provision for external DCC signal source

Project Files


The schematic and PCB layout were created using the Electronics Design tools provided by Eagle CAD.



  • Eagle CAD for Windows, Mac and Linux
  • SparkFun10mil.dru a 10-mil version of SparkFun's Design Rules Check
  • seeed-plocher-gerbers an EagleCAD cam processor definition file that you can use to create "gerber" and "drill" files for your fab house
  • makeboard shell script to collect EagleCAD's CAM droppings into a zip file for fabrication
  • SPCoast.lbr a EagleCAD library of parts used in these designs.