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BREADBOARDING

by Stuart Ball

Start ý Grounding ý Placing Copper Strips ý Power Wiring and Supply Bypassing ý Lead Wiring ý Test Points ý Surface-Mount Parts ý Other Tips ý Putting It All Together ý Other Techniques ý Sources and PDF

GROUNDING

A key area where many digital and microprocessor designs have problems is grounding. Early digital designs often used two-layer printed circuit boards, with power and ground traces mixed with the signal traces on the top and bottom layers.

As clock speeds and edge rates go up, simple grounds such as this are less effective. A modern production digital design will typically use one or more ground planes between the signal layers to get a low-impedance ground. It is difficult to duplicate this with most prototyping techniques. Ground wires connecting the ground leads of the parts work for low-frequency designs, but the overall impedance using this technique is just too high for many fast components such as ACT logic.

The heart of my prototyping technique involves the use of adhesive copper tape to make a ground plane, running the copper strips between the IC leads and around the edge of the board. This arrangement effectively makes a copper grid. The copper tape makes a low-impedance connection even at high frequencies.

Figure 1 shows two sketches of a prototype board using this technique. The cutaway view shows 8- and 14-pin DIPs mounted on a perfboard with copper tape on the bottom of the board run between the IC leads and around the edge of the board.

Figure 1ýCopper tape grounding provides low-impedance ground connections. (enlarge)

The vertical ground strips are soldered to the horizontal strips where they cross at the edges of the board. The ground pins on the ICs are connected directly under the IC by running a bare wire from the IC lead to the copper strip.

The full drawing in Figure 1 shows a complete board with several DIP ICs and a few discrete components mounted on the board. The copper tape attached to the bottom of the board is shown with dashed lines.

Bypass capacitors are mounted near the ICs, and one lead can be connected directly to the copper ground strip, just like the IC grounds. Any discrete component leads that are connected to ground can be bent over and soldered to the ground strip.

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