Dario Greggio <adpm.to <at> inwind.it> writes:

> wouter van ooijen wrote:
> 
> > relays driven directly by a PIC????
> 
> In theory, 5V (or 6v) low-current relays like those used in series with 
> telephone lines could work. Diode in antiparallel needed anyway!

Not just in theory. 10-15 mA relays (even bistable ones, even single coil ones
using capacitor coupling) can be driven ok by a PIC IO pin (or two in parallel
if need be). However, now the parallel suppressor diode must be Schottky and
that makes it more expensive.

Also, I don't make my circuits 'work near a piezo (I assume you meant thyristor
gas) lighter', but I have to be reasonably sure that they will work. That's why
susceptance testing (with an arc gap or piezo lighter) is done.

Vasile wrote that he tested PICs to 0.4-0.6 V. I tested 16f54 and with just one
pin at Vss-0.58 V (one 1N4148 to gnd) it was frozen like tuna, not coming out of
reset (and this was at Vcc = 5V). Worse, if this condition occurred after the
chip started working then the IO pins (effectively the whole core) would freeze
and the IO pins would maintain their state. This would cause e.g. an attached
pulsed IR led and other such devices to be destroyed if on. In case a PWM driver
would be attached the problem could propagate further, and a power device could
cause some smoke-letout events. Asserting reset would not help, so an external
watchdog would be needed to cut the driver power but this is now moving into
MCS51 territory where I use exactly such external hardware watchdogs to prevent
small disasters from happening.

Peter P.


-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist