Requesting your help with electronics and Arduino for my model railroad - Part Deux - The Signalling

[Paul Bartz]

Starting a new thread... hop[e this is OK, mods.

So, I've bought further into the Bruce Chubb CMR/I world with the acquisition and construction of two Searchlight Signal Driver boards to drive up to 24 bicolor LED signals. The SSD is pretty slick; it's got one resistor with series diode for the red aspect, another resistor with a series diode for the green aspect, and a trimpot to vary the duty cycle to give a fairly good yellow aspect.

I'm planning to use one, Arduino Mega 2560, for track detection and turnout position logic. With 12 blocks and 28 turnouts in this, I'll have some extra inputs.

This will talk to a second, Arduino Mega 2560, which will drive the SSD boards. 48 outputs (2 per signal) should be plenty.

Which leads me to the questions:

• The SSD board (12VDC supply) takes a pulldown on the inputs. Can I set the pinmode to OUTPUT on the second Arduino (5VDC supply) and connect the SSD inputs directly to the outputs, or should I add an additional pulldown or pullup resistor on each line?
• The DCC Optimized Detector has a pulldown transistor as the output. Can I connect the DCCOD outputs (12VDC supply) directly to the first Arduino's (5VDC supply) input pins, or should I add an additional pulldown or pullup resistor on each line?

 

[Paul Bartz]

OK. A bit more reading and head scratching.... let's see if I have this right. Resistor values chosen for 0.5mA current flow.

DCCOD > Arduino one. Tie the 12VDC and 5VDC power supply grounds together, 10k pull-up resistor to +5VDC on Arduino inputs.

Arduino two > SSD. Tie the 12VDC and 5VDC power supply grounds together, 24k pull-up resistor to +12VDC on SSD inputs.

 

[Paul Bartz]

I added 10k pull-up resistors to +12VDC to the Arduino outputs. The SSD inputs are still only seeing 0v and +5V (Arduino LOW and HIGH outputs) and aren't driving the signals correctly...

Help!

 

[Paul Bartz]

I'm going to try a 4-channel 5V logic to 12V logic optoisolator board. Pretty sure level conversation is what I need, now.

 

[dmsilev]

A level-shifter should work. Pull-ups won't do anything except cause some current to flow in the resistor; the Arduino will actively maintain 5 V (or 3.3 V, depending on the version you have) on a HIGH output. Which is what you'd want; driving that output line up to 12 V would be a good way to damage an Arduino that's not designed for it.