2007-07-06

Voltage visualization

I was connecting a Semaphore signal and I decided to try powering the light using the 5.1V DC supply and since it is an LED light I needed to get the polarity correct. My other color light signals also have LEDs and they all have their black lead with the diode connected to the common ground since the Viessmann signal modules produce a negative voltage relative to the common ground. My 5.15V DC supply is however positive relative to ground so the semaphore signal needed to have its yellow wire connected to ground and the brown lead with the diode connected to the positive power supply.

I realized that I needed to keep track of the various voltages I have available on my layout so I created this visualization.



It is just a visualization, I have no idea how the digital signal frequency and amplitude compare to the 16VAC supply. I don't recall how negative the DC current is that comes from the Viessmann signal modules. It does mean that next time I have to do something I can come back to this and know what is positive and negative relative to the common ground.

As it turns out, the 5 Volt supply combined with the resistor already in the signal circuit was too dim (since they selected the resistor for 16V AC) so I simply connected the wire to the nearest 16VAC supply bus after all instead of replacing the resistor with a smaller one.

Update 2007-08-12

I added the outputs of a Märklin 6080 loco decoder. The function output is about  -11 Volts relative to ground. With a capacitor this increases to -14.4V indicating that it is not a clean DC output. The motor outputs are never off and my meter measures between -5 and -15V of the pulsed width output. A capacitor locks this at -17 Volts.

6080 decoder wire colors: Yellow = f0 reverse, Gray = f0 forwards.  Green = motor forwards, Blue = motor backwards, Black = motor return, Red= digital, Brown = ground.

Note

I now use 12V DC instead of 5.1V for lighting and accessories, but the principle is the same.