The Zero Ohm Resistor


     Recently I was sorting through some storage, and came across an amusing bit of our history. At one point, two of our members were doing some consulting with a firm in Taiwan, and spent some time there. One of the things they came across was an ironic piece of electrical hardware‒the zero ohm resistor.


     The ohm is the unit of resistance. When electricity flows through anything other than a super-conductor, there's a back-pressure that is called "resistance." As energy flows, resistance limits the flow and converts part of it into heat.

     In Taiwan, there are huge companies and tiny companies. The larger companies generally combine components into assemblies, the components being produced by the smaller companies who specialize. A small company's size (minimal overhead) and ability to specialize allows them to create and exploit small niches within the larger industrial ecology.

     Resistors are commonly used in electrical circuits to limit the flow of energy through a component. For example, an light-emitting diode (LED) converts some of the energy flowing through it into light. If an LED were to be hooked up directly to a power source, too much energy would flow through it and it would "burn out." To prevent that from happening, a resistor is put in series with the LED. The resistance needed in a specific circuit is a function of the circuit voltage and the ability of the LED to convert energy into light.


     A resistor's ability to limit the flow of current is marked on it's surface using a color code. The first color represents a digit, the second another digit, and the third the number of zeros following the first two numbers. For example, a common value for a resistor controlling the current flowing to a standard LED would be 330 ohms, and would be marked with an orange band, another orange band followed by a red band. For a full description of resistor color coding, Click Here.

     So, what's the point of making a resistor with zero resistance? Sort of seems pointless, doesn't it?

     Back in the early days of printed circuit boards, it was often necessary for one line on the circuit board to "jump" over another. Today, the development of double sided circuit boards, "through-hole" plating and even multiple layered circuit boards makes the need for a physical jumper rare, but back in the early days, jumpers were common.

     When making a small run of boards for some special purpose, homemade single sided boards are useful, and in line with our commitment to retain as much entry-level technology as we can. In our case, we'd just take a short length of copper wire, bend it into the appropriate "U" shape, and solder it in. That's fine for a few boards, but back when larger circuits required dozens of jumpers, there was a need to automate the process.

     Once upon a time, all components were installed and soldered by hand, but gradually machines were developed to automate the process. One of the first such machines was able to install all the resistors called for on the board. The body of the resistor made for a convenient place for the machine to grasp the resistor, bend the legs and insert it into the board.

     This is where the zero ohm resistor entered the picture because it enabled the $90K machine that stuffed the resistors to also insert a jumper masquerading as just another resistor. I recently came across a picture that shows that the concept of the zero ohm resistor has made the cross-over into the world of tiny surface-mounted components.


     My point in writing this article is to share a tiny bit of Windward history that points to the odd little market niches that can evolve when one develops the ability to look at existing systems in novel ways. A lot of Windward's history has involved doing just that.

Notes From Windward - Index - Vol. 71