For the BD20 to work correctly, ALL feeders for the detected section must go thru the BD20. The best practice is to have one BD20 per feeder and only one per section of the track. That section should be isolated from all other areas using gaps or insulating rail joiners. The BD20 must be as close to the detected section as possible to avoid false detection triggered by long cable runs.
False Triggering:
You may get a false detector triggering if the block is too long. The capacitance between the rails conducts a small amount of the DCC signal and can cause the sensor to trigger. If you have problems with this, see the desensitizing detector section.
Desensitizing the detector:
If you have problems with false triggering due to humidity, ballast glue, track oil, etc., providing a conduction path for the DCC track current, a resistor or potentiometer may be installed on the PC board to desensitize the detection circuit. Figure 3 shows the location of the desensitizing resistor mounting holes. The resistor or pot should be 1/4 watt or more. The value is determined by
adjusting the pot. You can use a pot to determine the correct resistance for the block, then substitute a fixed resistor of the same value for the pot. The deal is typically in the range of 500-10K Ohms.
We suggest a 6mm 5K-10K pot. Digikey (1-800-DIGIKEY - www.digikey.com) offers suitable pools.
Bournes 3362P-1-501LF is a good replacement
https://www.digikey.com/en/products/detail/bourns-inc/3362P-1-501LF/1088420
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