Propeller Simple Spin Board Part 4 & 5

Experiment 4: crisscross wiring

PART 4 & 5 - IMPROVING RELIABILITY
PROPELLER SIMPLE SPIN BOARD
The Propeller Simple Spin Board will be expanded more in the future. Let's make some preliminary preparations for this and improve its reliability. While in it's RC speed state with RCFAST and RCSLOW, the circuit is already reliable and durable.

Experiment 5: decoupling

 









However, at higher clock speed, overclocking, with unusual loads or demands, electrical pressures and imbalances occur internally inside the chip, which is also effected with various operational configs. These conditions are not always for the better. However, it's possible to improve the operation of these circuits with external wiring and components.

Although it's a lot of technical mumble jumble jargon to describe it, basically the Propeller needs decoupling capacitors on each side of the dip chip, as close as possible to Propeller pins VSS and VDD, and a special added "criss-cross" wiring. Propeller experts say both the connective wiring and the capacitors (use a .1 uf value) belong to the chip and help to prevent blowing out the PLL circuits inside the chip.

The wiring connects one side of the chip to the other side. Ground VSS on one side (use a green or black wire) is connected to ground VSS on the other side, and power VDD (use a red wire) on one side is connected to power VDD on the other side. Use shortest wires that run directly over the top of the chip. This circuit will balance the chip's internal circuitry and help prevent a condition that could damage the chip. With these improvements installed, the Propeller chip is ready to run extremely fast and do much more than we ever expected. Stay tuned for more.

Another possible requirement involves using the addition of 10uf and 100uf capacitors for when the Propeller is expanded with additional demands. Due to limitations of breadboard pins nearest the chip, these capacitors may or may not connect at the power rails position.

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.

SOLDERLESS
BREADBOARD GUTS

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)




SOURCES
(1) http://wiki.analog.com/university/courses/electronics/electronics-lab-breadboard-coupling
(2) http://en.wikipedia.org/wiki/Breadboard
(3) http://forums.parallax.com/showthread.php/124495-Fill-the-Big-Brain/page62