The BasicDCC Project

BasicDCC Booster

I needed a DIY DCC Booster to go along with my DCC controller project.
While looking around the net for further information, I stumbled upon
various Stepper Motor Driver modules that would appear to handle the
switching and current requirements for a decent 3amp DCC booster.

I picked up a few of the different driver modules from the internet and
looked at the NMRA specs to see how to interface them to a standard
DCC controller.

The NMRA specs state that the input of all boosters must be optocoupled
when connected to an approved controller. This ensures that the controller
won't suffer any damage in the event of a serious booster failure. I wanted
my booster to be compatible with the various controllers available on the
market so I decided to go with an optocoupled input.

I settled on a straight forward voltage divider circuit with reverse voltage
protection that feeds either a PC817 or 6N137 optocoupler. This provides
ample protection to the controller while meeting the NMRA spec.

I also needed some way of handling the SIGNAL DETECTION, FAIL SAFE
and OUTPUT LOGIC functions. I settled on the ATTiny microcontroller to
take care of this. This tiny 8pin chip has plenty of code space for the task
and enough output drive to feed the various driver modules directly.

I laid out the design and named it the BasicDCC Isolator. I built it up and
tried it with the driver modules that I ordered. Some smoked at less than
1amp and some handled heavier loads quite well.

I ended up settling on a module based on the L298N that fit my 3amp target
nicely. It is actually rated at 6amps but I like things to run cooler, so I treat
it with a 3amp rating. This leaves plenty of head room.

It works well with most 12-16vdc power adapters with a rating of 700ma -3amp.
(That old laptop power adapter works well if the voltage is within tolerance).

I found that an adapter rated at 700ma runs 4 Atlas N Scale locos quite well.
I had 9 locos running with a 3amp source and the L289N was just luke warm
after an hour of continuous running.

The Microcontroller

The ATTiny25/45/85 processors will also work in the circuit

The ATTiny25/45/85 processors will also work in the circuit

The Opto-Couplers

The board has been laid out to use either the PC817 or 6N137 optocoupler.
The difference between the two optocouplers boils down to the type of output
provided by the device.

The 6N137 has a digital TTL type output that is designed for compatibility with
TTL devices. The output is fed by a comparitor that sharpens the output and
brings it into TTL spec.

The PC817 has an fast open collector type output. The output is fed directly
from the detector and has slower rise and fall times that require sharpening.
Luckily, the input pins of the ATTiny processor do a great job of sharpening
the signal and can accept the output of the PC817 directly.

Both have similar inputs that feed the internal LED directly so the same input
circuitry can be used for either device.

The PC Board

I planned to experiment with the optocouplers and microcontroller so I used
machined pin IC sockets for both of these devices.

I find that placing the microcontroller into a separate socket and using it as a carrier
while programming, allows for easy in and out. This avoids bending the pins on the
microprocessor and reduces issues due to socket wear.

The Driver Module

The drive circuit is built around an L298N PCB module that easily handles the
3amp drive with pretty decent built in short-circuit protection. I ran with my
breadboarded prototype for almost a year and it stood up well to the many short
circuits encountered along the way.

* Isolator Wiring Chart *




The End Result

This basic DCC Booster was developed to be experimental in nature and is ideal for the
hobbyist that wants to delve deeper into DCC circuitry. It also works great, right out
of the box with most brands of controllers (minus any advanced proprietary functions
the manufacturer incorporated).

I decided to combine the project onto one board and have built a few up. I'm
offering them on Ebay as DIY Kits as well as Assembled and Tested units.

Assembled and Tested Unit


Copyright 2019 .. BasicMega