Breakout Boards

Breakout boards are a common electrical components that take a bundled cable and “breaks out” each conductor to a terminal that can easily accept a hook-up wire for distribution to another device. They are a common item in electronic projects and enable easy, clean installation of electronic devices. The image at right shows a simple DB25 breakout circuit board from Winford Engineering. The breakout board is positioned between your computer or indexer and the motor drivers and serves two purposes in the CNC control system: circuit protection and signal distribution. Here we will describe the board’s function in the CNC control system and what you need to know about how to select one to suit your needs.

Let’s say, that you have three simple bipolar stepper motors , each with the normal 4 wires. Your wiring schematic would look something like the following:

At left, there are three signal pairs coming from the computer, one for each stepper, and a ground line for the return as indicated by the small black line under the three pairs of signal wires. For a typical DB-25 cable, the ground is the outer jacket of the connector.

Opto-couplers are small optical “switches” that isolate circuits to prevent an electrical short from one circuit affecting another. In this case, the opto-couplers protect your computer from a short from your motors or switches. Many high end motor drivers offer their own opto-isolation system.

You may also see boards that include their own power distribution internally with fuse protection. This setup is more common on lower voltage systems, such as 12V systems. For these setups, your schematic will look like this:

Connector Type – Breakout circuit boards are a common item to electronics, and not specific to the CNC industry. There are literally thousands of them from which to choose. In most cases, you will want a setup with a female DB25 computer cable connection on one end, and screw-post terminals on the other.

Number of I/O Signals – In most cases, the DB 25 cable interface will give you as many as 24 I/O signals and one common ground. If you exceed this capacity, you may want a second breakout device connected to the DB9 port on your computer. For a discussion on hooking up your board, please see the breakout board hookup section.

Power Distribution – As described previously, some breakout devices allow you to distribute the power from the power source to the motor drivers. Others simply distribute the signals and require direct hook-up from the power source to the drives, bypassing the actual board. Some boards require external power, and if your power source. Be sure to read the manufacturer’s specifications carefully and plan accordingly. For more information on power sources, please click here.

Circuit Protection – Most breakout devices are passive devices that do not offer circuit protection, such as that shown at the top of this article. For CNC applications, it is highly recommended that you use an active breakout device with some type of circuitry protection. The most effective solution involves the use of opto-isolators that use pulses of light to transmit information across an air gap. Others will have fuses that prevent excessive current passing through your computer.

Feature – Some boards are specifically designed for CNC devices and offer nice features that enhance your machine.

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