Re: Positioning Block Detectors for AIU-01
Don is right on…..
Clarification…The output of a BD20 itself is not that sensitive to noise. From a noise standpoint Its got a huge capacitor (0.47uF) directly across its output. AKA a noise short circuit. The AIU input also has some RC filtering but has a very low threshold of detection (TTL) that is not the same as the LED indication threshold (CMOS). It is more sensitive than the LED indications would indicated. Anyway, what this means is the noise gets in is the cable running between the BD20 and the AIU and it can create false/random states.
But to be clear, do not move a BD20 further away from it detected block out of interest of getting it closer to the AIU. Optimize the location of the BD20 first and then after that is done, given the locations of the BD20, figure out a common central place for a AIU to pick up a lot of them.
Steady state problems are easy to fix. But what typically happen on a layout is they are not steady. They appear to be random and mysterious for it depends on what is running or not on the layout and where the trains are. It like there is a ghost in the wiring. There is no ghost. It just understanding what if happening with regard to the wiring. The BD20 to AIU wiring is less of a problematic issue than the BD20 to the block wiring basic detection reliability issues. Also if there is a problem, its a lot easier to fix the BD20 to AIU cable wiring than it is to fix the track block to BD20 cable wiring. Never run/bundle a BD20/AIU cable in with a DCC track bus cable paths. It is perfectly OK to run one or multiple BD20/AIU cable along or in the Cab bus cable path.
AIU Utilization: Remember your AIU also typically include turnout position feedback. If you have a multi level layout, think about a given AIU picking those blocks and turnouts that are not that far away wiring distance wise. HOWEVER, is is better to have multiple AIU than to FORCE one AIU to pick up all the BD20 and Turnouts on a large layout. If you running more than a 1/3 of the AUI connection a long distance of 25 feet or longer, then it time to START thinking about getting another AIU and/or twisted pair wiring. Twisted pair wiring address the noise pickup issue between the BD20 and the AIU up to a point. Just use twisted pair wiring up front and help yourself in the long run at the time of installation.
Door bell wire historically has been sold in basic 2 wire twisted pair format without a jacket. Red and White are common wire pair colors. Being a unique combo color code, it will be easy to identify the cable under the layout in the future.
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