sparks from a (clock) crystal!

[[email protected]]

I tossed together a little dual-hcmos inverter crystal oscillator
yesterday to use as a marker generator while trying to tune a receiver.
At one point I put an old HC-6 (ie, big) 1 mhz crystal in it. One of
the leads was broken off short, so it was kind of wedged up against
another component lead temporarily, in a way that let me key the
oscillator off and on easily.

It sparked! Tiny blue flash at the intermittent connection.

Not totally unreasonable given that piezo crystals are used to do that
intentionally in grill ignitors.

Suprising thing though is that the 74hc04 does not appear to have died.
When it's not making sparks it oscillates about as I'd expect.

 

[Dave Farrance]

I tossed together a little dual-hcmos inverter crystal oscillator
yesterday to use as a marker generator while trying to tune a receiver.
At one point I put an old HC-6 (ie, big) 1 mhz crystal in it. One of
the leads was broken off short, so it was kind of wedged up against
another component lead temporarily, in a way that let me key the
oscillator off and on easily.

It sparked! Tiny blue flash at the intermittent connection.

Not totally unreasonable given that piezo crystals are used to do that
intentionally in grill ignitors.

Suprising thing though is that the 74hc04 does not appear to have died.
When it's not making sparks it oscillates about as I'd expect.

In theory, the diode clamps should shunt the excess through the
substrate. It's only if the current exceeds a few hundred milliamps
that a CMOS device goes into lockup and shorts Vcc to GND.

I've seen a graph showing the effects of a spark on a TTL 7400, and
although it continued to work, its output slew rate was cut by more
than half. I expect that CMOS devices can also be "slightly fried".

 

[Frithiof Andreas Jensen]

[email protected] wrote:

I've seen a graph showing the effects of a spark on a TTL 7400, and
although it continued to work, its output slew rate was cut by more
than half. I expect that CMOS devices can also be "slightly fried".

Oh Yes!! CMOS are notorious for "medium rare" effects that shown themselves
after many units have been sent to faraway locations in great volume. That's
what gave us the whole ESD-awareness circus in the 1980's.