How do install a Locofi decoder into DCC ready model, do I plug it in like a standard decoder or is more involved such as hardwiring and soldering.
You're welcome! Welcome back to the hobby! Please keep us posted with your progress. Thanks.
Thank you for this very useful and complete information.
With LED forward voltages in the 3 to 3.3 Volt range, I agree that 3.3 Volts is not going to provide a usable amount of light from the LED if there is a 1K series resistor. You must drive the LEDs directly from your logic outputs.
I am returning to model railroading after decades of working as an electrical engineer, and this is the first time I will be installing a decoder/controller of any kind in a locomotive. The target is a Bachmann Baldwin 4-6-0 that is "DCC Ready", and the control boards go in the tender, where I hope I may have some extra room to make the installation go more easily.
I'll keep you updated as I go along with the installation.
You are correct in that the track and motor wires can be connected to the DCC ready plug as it is. However, lights are not as straightforward. See below for an explanation.
A simplified schematic of a typical light board is shown below. Please note that that only the portions relevant to lighting are depicted.
TR1 & TR2 - Track power
S1 & S2 - These switches represent if the dummy plug for DC operation is connected (switches closed)
L1 & L2 - Light outputs
R1 & R2 - Resistors (typically around 1k)
D1 & D2 - Diodes
LED1 & LED2 - The light LEDs
For DC operation, the switches would be closed and as the polarity on the rails is reversed, the appropriate LED will light up.
For DCC, the switches are open and the white and yellow wires connect at the points L1 and L2. V+ is common positive. Now the L1 and L2 are always HIGH when the lights are off. When L1 or L2 or both go low, current will flow and light up the appropriate LED(s). Typically V+ is 14V and resistors are up to 2k. The current flow will range from 5mA to 20mA depending on the value of the resistors.
Even if LocoFi™ module was common HIGH (V+), that would be a voltage of 3.3V and the LEDs will never light up due to the high value of resistors. LocoFi™ design philosophy (and it can be argued) was that the output go HIGH only when turned "ON" and the current sink to GND.