Not sure if this is of any use but I've just measured the 1PPS output
of my Reyax UP501 GPS module on a 'scope, 2.8v. (Module runs on 3.3v).
I know that this reliably triggers the ATMEGA enough for it to work
with the signal.
But I know that if put a current limiting resistor in series then
it will not work at all (a 2K2).
Trying to measure the pulse on a DMM or even an analogue meter
will show about 0.7v due tho the rise time restriction of such
meters.
73 de Andy G0FTD
