I received the PCB the other day. I had discussed the design ideas for this PCB in Part 1.The request was for yellow solder mask with black silkscreen. As you can see from the picture above, it is more orange than yellow. I think there was too much RED left in the solder mask machine when
they applied the yellow. Oh well it is
different and the price for a 4 layer was still very good. Hopefully there wont be any other problems with the PCB.
Here is the digital part working.
All of the digital uses 3.3VDC. The power section takes 16VAC
(train layout voltage) and generates 20VDC+ (straight out of the
full wave bridge with some capacitance) for activating the turnout/signal relays and then generates 5VDC (for
LEDs and relay bias control) with a small DC-DC converter. The
3.3VDC is generated from a small LDO. Look close to the right of
the push button and below the jumper and you can see a space wired
SOT23 device. The LDO was supposed to be a SOT223-3 device. My
first choice was a MCP1825ST, but was out in time to next Xmas, so I found what I thought
was a pin compatible LDO, it wasn't. Now I have found one (triple
check), but I thought I would wait a few more days to see if
anything else needs replacing.
The jumper selects either the Power Section 5VDC or VUSB. That way
I can power the digital section without the train transformer and
still do debugging and programming. The Analog Discovery 2 from Diligent is helpful
when looking at changing outputs. With the 34" monitor, I can run a
remote desktop window for my other laptop which is running the
Digilent Waveforms and the PC program that interfaces to the PCB. The main
laptop has the MPLABX and ICD connection.
Next up is the power section. The DC-DC converters came in today,
we will see if the Asia reseller market has real parts.
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