Hi Mark,

About the bits and pieces, I hear what you say and I'm planning to report this adventure on my website. But understanding MFX took some time, making the electronics, writing code and setting up a website will take some time too and I'm not retired yet.... So I've to divide my time.
I studied your coding work and alternative RDS decoding circuit. Kudo's! Your way of coding resembles my way of coding which made life much easier...
But I want to think out of the box and make decoding simple by trying to lose the RDS chip(s) and solve the decoding in software. Decoding from a controller standpoint is easier because you know whenever a decoder start talking. This means that (all) available resources in your processor can be used to decode. BTW I use a Wrover ESP32 but I'm thinking of switching to a ATOM Lite M5 to make everything nice and compact.
Coming back to the signal decoding. To be able to measure the signals which I generate with the software and the ESP32 I placed a resistor in between the driver and the track. The resistor value is too high to drive multiple loks but good enough to drive one lok and to measure signals going back and forth with an oscilloscope. Now the decoder uses a current source to talk back. The current from my DHG700 lok is 100mA. If I would change the resistor value to 0.2 ohm the voltage over the resistor, containing the feedback data, would be 20mV. Yesterday evening I was playing around with LTSpice, a free electronics simulator, and came up with the following circuit:



This circuit I created detects edges of digital pulses and outputs them to a 3.3V level suited for the ESP32. The simulation result looks like this:



The green signal is one side of the +/-18V signal on the track. After 250us I start to simulate a 1 bit feedback signal (should be 20mV and not visible in the simulation plot). The blue signal is the output signal on the collector of Q2 that should be used as a signal to the ESP32 for decoding. Simulation shows it should work but I'm not happy yet. First of all the feedback signal, when using a 0.2 ohm resistor, is very low and therefor sensitive for interference. Secondly the power in the series resistor, when pushing 10A, is 20W, which is a lot. Thirdly there would be a voltage drop of 2V.
So my thinking cap is still on how to improve on this.


U2 a Merry Christmas and keep you posted.

Greetings,
Roland

Hi Mark et al.
Progress... I've been busy in between Christmas festivities and the project starts to show some lift off. Ready? Here we go:

1. I call the electronics and software I'm working on "The ATC", short for "The Alternative Train Controller" (you need to call it something).
2. Exchanged the ESP32 Lolin32 dev.controller board for an Atom Lite ESP32. This makes the footprint of the ATC 100x 70 mm.
All pins of the Atom Lite are used but spared two pins for an I2C interface (for future expansion).
3. Finished, build and tested the Feedback electronics.
4. Included Bitstuffing


In a previous post I showed a Feedback circuit that worked but was component critical and potentially could absorb a lot of power. Like kiwiAlan mentioned I also thought of a solution with a transformer. After some designing and simulating I came up with the following solution:



According to the simulator it should give the following result:



The green trace is one side of the +/- 18V track signal. The blue trace is the signal on the collector of Q1. Please note that for visualisation purposes I decreased the 18V to 5V and pause time for a 1-bit feedback from 6.4ms to approx.0.5ms.
Mind you the 28uH coil still gives an high inductive resistance for the frequencies used in a MFX signal (period times 50us, 100us and 19us). But that's something to solve/improve upon later.
After building the circuit I included an interrupt function in the ATC software capable of capturing the 52.63kHz signal from a decoder when respoding on a 1-bit feedback. On an oscilloscope (In Real Life) it looks like this:




In the top window you see a 'Decoder Search command with 1-bit feedback' frame. The signals are the trigger signals (Purple) showing the start of certain events within a 'Decoder Search command with 1-bit feedback' on broadcast address 0. Yellow, signal on the track. Blue the output of my circuit. Bottom window, a zoomed in view of the beginning of the pause period.

When giving a Decoder Search command my software responds with:

Write frame in array bitArray to track: 10 0000000 111010 000000 00000000.00000000.00000000.00000000 01110010
1-bit response confirmed. Number of pulses counted: 337

10 0000000: 7 bit format address 0
111010: Decoder Search command
000000: counter
00000000.00000000.00000000.00000000: 32-bit decoder address 0
01110010: CRC

The number of 19us pulses I expect within the 6.4ms response windows is 336. The software counts 337. Good enough for me to deside for a positive 1-bit response.


The Bitstuffing, include a zero after transmitting eight ones, looks like this:




Next stop finding out the decoder address (UID).

Greetings,

Roland

Hi Mark,

the ferrite core looks like this:



The actual dimensions can be found in the schematic in the previous post. It was a core that I had laying around. I didn't any specs on it. I determined the induction by adding a parallel capacitor and applying a sine wave. Based on the resonance frequency I could calculate the inductance of the coil. Then plugging in core dimensions and inductance in a 'ferrite core calculation program' I found on the internet I could make an assumption of the ferrite core specifics.

BTW I managed to retrieve the ID of the DHG700 lok, being 7df8dd24 and from the LokPilot5 module f9ee151c.
I can also successfully ping to the lok.

I'm getting close now.....

Greetings,

Roland