Hi all,

At 02:08 PM 1/30/99 -0500, you wrote:
>At 06:23 PM 1/30/99 +1000, Paul B. Webster VK2BZC wrote:
>>Sean Breheny wrote:
>>
>>> and no ground plane is available in either case (so "star" grounds are
>>> the only way to avoid ground loops in either case).
>>
>>  You've got me puzzled there.  What are these "ground loops" you are
>>trying to avoid?
>
>
>If a circuit grounds at two different points, then it is suceptible to
>current flowing in the ground.
>(Ground IS a signal!)  For example, I have a project where I am running a
>stepper motor at 1A, next to a head amplifier with a gain figure of 7000.

Yes, this is what I meant by ground loops. I am in the midst of a project
right now where this sort of thing affected me greatly. It was a real
learning experience! I just completed a design for an adjustable 3Amp power
supply. I wanted to keep output ripple below 5mV. If I used different
ground points for my voltage reference and my main output ground, and there
was a significant current flowing between them, I saw not only about a
100mV drop in the output voltage, but more importantly, a 50mV ripple.
Making these grounds the same point decreased it to 5mV. I even find this
true with little 78xx regulators. They are really decent regulators if you
make sure that you connect the return line from the stuff "downstream"
directly to the 78xx's GND pin. If you connect it further back, like back
at the rectifier, there will be a voltage error and a ripple voltage
proportional to the current and the resistance of the intervening wire. I
saw this first hand on my scope.

Regarding breadboards: I understand what Byron is saying about mechanical
stability, but usually this isn't a real problem for me. Just as Larry
pointed out, if one resists the temptation to use arbitrary length wires
and actually uses ones of appropriate length, this usually isn't a problem.
Just like Larry, the only time I really have a problem is when I try to
attach external components. It would be nice to find breadboards with mass
termination connectors built in. Anyone seen these?

Thanks to everyone for the comments. I think I will stay with breadboards
for now, but consider wire wrap for anthing that requires especially strong
mechanical connections in the prototype stage.

Sean

+---------------*----------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+---------------*----------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
mailto:shb7@cornell.edu  Phone(USA): (607) 253-0315 ICQ #: 3329174