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First of all I’m not electrical engineer. The original idea is described here.

It is a model railroad problem. The rails are carrying a power signal (DCC) 12-18 V. The frequency is ~17 kHz. It is a square wave signal described here.

The circuit swaps the hi and low rails when the short occurs. This it happens at the gap between two insulated parts of the rail track with the hi and low rails not corresponding. When the train wheel bridges the two unmatched rails we have a short. The reverser has to detect this at a lower level of the boosters amper limit and switch the signal to the rails of the reverse section.

In the original circuit, I replaced the shunt with an ACS712 current detector. I replaced the other parts in the circuit with parts that are available in Ltspice to simulate it. The original circuit checks and the second gap. In my scheme is only the detector for one gap.

  • Will this circuit work?
  • Is the ACS712 sensor a good replacement?
  • What are the suitable DIP components?
  • Can I "catch" the output from the 555 with an Arduino and switch the relay?

I have and other thoughts like set the comparator's limits with a potentiometer or from Arduino.

I hope the comments in the LTspice schematic will help. Any thoughts and critique are welcome. I didn't find a way to attach the LTspice file.

multiple shorts

short circuit detector-auto reverser circuit

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Will this circuit work?

Do you have any reason to doubt the simulation? Looks fine to me.

Is the acs712 sensor a good replacement?

Sure. The bandwidth is adequate. You just need to pick the correct sensitivity range for your application. (5A, 20A, 30A)

What are the suitable DIP components?

We don't do product recommendations here. But your favorite distributor's website (Digi-Key, Mouser, etc.) will be able to help you there.

Can I "catch" the output from the 555 with an Arduino and switch the relay?

Sure, no problem.

I have and other thoughts like set the comparator's limits with a potentiometer or from Arduino.

Also no problem.

But if you're going to throw a microcontroller in there anyway, you can simplify the circuit considerably, eliminating the comparators, the 555 and the DFF. Just digitize the output of the current sensor directly (ADC with an adequate sample rate), do all of the logic in firmware, and switch the relay driver as needed.

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  • \$\begingroup\$ Thank you and I appreciate your effort to correct my english and the appearance. My concern was if there are any special requirements about the Dip parts. I have to read more about the sensors with ADC. The sensor with the ADC requires a shunt resistor. The acs712 is based on hall effect. Can they cause signal distortion? \$\endgroup\$ – Vasilis Jul 1 at 8:10
  • \$\begingroup\$ Distortion of the DCC signal going to the track? No. \$\endgroup\$ – Dave Tweed Jul 1 at 11:03

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