Saturday, July 13, 2013

Solderless Breadboard Guts

Breadboard polymer form and springs - note how the springs tightly insert into the board's polymer form. In the middle is a pile of springs, each will hold 5 wires in this breadboard version. At bottom is a disassembled power bus. This is one long conductive metal strip of springs.


We took apart a solderless breadboard and removed the guts inside to see how it works. Don't worry, the breadboard was already defective and only the end hole strip where one bus bar was missing. The photos tell all.

The link shows how to measure the extra capacitance on the breadboard. Measuring resistance is more simple - just measure ohms from the two farthest holes.

Pop open a solderless breadboard to see what's under the hood. With some care, the top lifts up while a good number of springs remain stuck to the sticky backing. A wire cable is shown for comparison. Note some of the green faced sticky backing peeled away.

"When building an experiment on a solder-less breadboard, you add the small (stray) capacitor between adjacent rows of connection points to the circuit. This is because the way the solder-less breadboard is built, it has rows of metal connection strips laid side by side (0.1 inch apart) separated by plastic dividers. Because the strips are fairly long and they are in parallel, they have a significant capacitance between them."(1)

"Due to large stray capacitance (from 2-25 pF per contact point), high inductance of some connections and a relatively high and not very reproducible contact resistance, solderless breadboards are limited to operation at relatively low frequencies, usually less than 10 MHz, depending on the nature of the circuit. The relatively high contact resistance can already be a problem for some DC and very low frequency circuits. Solderless breadboards are further limited by their voltage and current ratings."(2)

Showing two decoupling capacitors
The extra capacitance from the layered bus bars may actually contribute more effectively to the Propeller chip's required decoupling capacitance. There are physically four pin layers on the breadboard at decoupling capacitor's position that may yield up to 100 pf. However, the recommended decoupling capacitance for each side of the Propeller DIP chip is 100 nf so decoupling capacitors are still needed. (0.1 uF = 100,000 pF)