Hi Terry
On 04/10/2018 12:22, Terry Coles wrote:
I still don't understand why the inputs were sitting at 2 to 3 V with nothing
connected. Unless my Ohms Law is rustier than I thought, there can be no
input current if there is no connection. Normal logic gate inputs might float
a bit if they are left disconnected, but they normally wouldn't deliver enough
current to destroy a Pi!
There's an internal current source and it's settling at that voltage with no
load to source current into.
This is not the type of circuit which lends itself to breadboarding. Lots of
high peak currents so need really good ground and power planes and careful
decoupling.
I only stuck the chip onto a breadboard (in isolation) to try to understand
the input voltages that I was seeing. I assume however from your comment,
that Veroboard would be no better than breadboard for this circuit,
I have in the very distant past breadboarded similar circuits on perf board
with solid copper planes. All the grounds can be soldered to the plane on one
side and power to plane on other side. Then spot face cut with a regular spot
face cutter (power/grounds) or annular cutter for non-power/ground pads. But
even then you really end up with too much inductance on other critical signals.
Much easier to lay out a PCB.
Cheers
Tim
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