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ROHS DEMYSTIFIED 379

No

Ground loop

Yes
Figure 30- 16 A ground loop is
when there is more than one path for
the ground connection. Ground loops
can cause erratic behavior in circuits.
Always connect the ground leads of
Ground all subsystems
to a common point components to one central point.

of the noisy component. Some designers like to use a decoupling capacitor on every inte-
grated circuit, while others place them beside every third or fourth IC on the board.
It’s also a good idea to put decoupling capacitors between the positive and ground connec-
tions of any circuit at the point of entry of the power supply wires. Many engineering texts
suggest the use of 1 F to 100 F tantalum capacitors for this job. Remember that tantalum
capacitors are polarized— they have a + and a side. Be sure to properly orient the compo-
nent in the circuit, or the capacitor (and maybe some other parts) will be ruined.

KEEP LEAD LENGTHS SHORT
Long wire leads on components can introduce electrical noise in other parts of a circuit. The
long leads also act as a virtual antenna, picking up stray signals from the circuit, from over-
head lighting, and even from your own body. When designing and building circuits, try to keep
lead lengths as short as you can for everything. When soldering, this means soldering the
components close to the board and clipping off any excess lead length.

AVOID GROUND LOOPS

A ground loop is when the ground wire of a circuit comes back and meets itself. The positive
and ground connections of your circuits should always have “dead ends” to them. Ground
loops can cause erratic behavior and excessive noise in the circuit. See Figure 30- 16 for a
visual depiction of a nasty ground loop that almost guarantees problems.

RoHS Demystified

Ever wondered about that “RoHS” thing that you see with many other electronic parts
these days? RoHS standards for Restriction of Hazardous Substances directive, a

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