ATOM DCC Block Detector
The Iowa Scaled Engineering ATOM is a reliable, easy-to-install, single-channel DCC block detector. Compatible with a wide variety of other block detectors on the market, the ATOM provides two open collector outputs (one for detection, one for no detection) with optional pull-up resistors and easy pushbutton sensitivity adjustment. Since it's based on a current transformer, the detector maintains isolation between your track and signal systems.
This version has screw terminals for the power and output connections. For our friends invested in C/MRI, we offer an alternate version of the ATOM (part number CKT-BD1-CMRI) with a plug that connects directly into the C/MRI detector motherboard and provides a drop-in replacement for the DCCOD.
Features
- Isolated, current-transformer based detection for DCC
- Highly sensitive (~1mA, equivalent to a 10k ohms)
- Simple single button sensitivity adjustment
- Two opposite polarity, open-collector outputs (40V / 250mA capable)
- Optional built-in 10k output pull-up resistors
- Powered from 5V to 24V
Typical Applications
- Detect block occupancy for signal systems
- Activate grade crossing signals
- Trigger sounds
- C/MRI track occupancy inputs
Specifications
2.0"(L) x 1.5"(W) x 0.875"(H)
Documents
Schematic (v4.1)
The complete gEDA design files and source code are available on GitHub.
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$19.00
- 6 or more $18.00
- 12 or more $17.00
- 50 in stock

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News & Application Notes
Block Detectors Are Back!
After nearly four years, it’s finally back!
I’d like to introduce the new ISE ATOM – the Advanced Train Occupancy Monitor. It’s the next generation of our old CKT-BD1 DCC Block Detector. Many of you have asked when it was coming back, and judging by the people who have already ordered a good number of them as soon as I got the store updated, there’s clearly demand out there.
Some of its key features include:
Introducing the CKT-BD1 DCC Block Detector
I’d like to introduce you to ISE’s latest model railroad product – the CKT-BD1 single channel DCC block detector!

This little DCC current-based detector is designed to be highly sensitive while being resistant to false triggering, robust, and very easy to install. All you need to do is pass one of the bus wires to the block to be detected through the current transformer and provide 5-18VDC to power up the detector.  It can run on as little as 5VDC at 15mA, so it’s perfect for connecting to digital logic such as Arduinos or C/MRI systems.  It has open drain outputs for both detecting and not detecting states, so it’s compatible with a wide range of other model railroad products such as the Modular Signaling System, C/MRI, input modules for systems like JMRI, standalone signal sytems, or even just seeing if there’s something in that hidden section of track on your layout. It also has adjustable sensitivity, so you can tune it to ignore leakage current through your trackwork while still picking up minute currents from rolling stock. Precision current measurement circuitry and a little digital microcontroller onboard helps filter the response so that you achieve maximum sensitivity without false triggers.
Block Detectors – An Epic Tale
The development of ISE’s block detectors has been a fairly long adventure, so much so that the long, drawn-out development cycle through six or seven iterations has become a bit of a running joke between Michael and myself. It’s served as a bit of a high water mark in terms of design revisions and major overhauls, and every time Michael and I have to rev something, there’s usually a comment of, “well, at least it’s not the !@#$ block detectors again…”
With today’s introduction of the CKT-BD1, I thought it might be interesting to let you all in on how this evolved, and how we arrived where we are today – a rock solid design that I believe in as much as our bulletproof IR sensors. It’s the sort of thing that no sane manufacturer would do – sort of like running the corporate dirty laundry up the flagpole and waving it around. But then again, we’re a different sort of electronics company, and Michael’s been arguing for years that I’m not quite sane…