02-05-2012, 12:42 PM
Versatile CMOS/TT L Logic And Clock Probe
CI-01_Feb08.pdf (Size: 323.43 KB / Downloads: 36)
For fault diagnosis of any logic
circuit, you need a probe that can
test the logic level or existence of
clock activity. The circuit shown here
can be used to test CMOS and TTL
logic circuits for logic states and also
for the presence of clock activity from a
few hertz to more than 10 MHz, at any
point of the logic circuit.
Supply for the probe circuit is
taken from the circuit under test using
alligator clips. In the circuit, LM319
dual-comparator is connected as a
window detector. The non-inverting
pin of comparator N1 is biased
to nearly 2V when switch S1 is in
TTL position and 80 per cent of Vcc
in CMOS position. The output of N1
goes low only when logic input at the
probe tip exceeds the biasing voltage
and, as a result, the red LED lights up
to indicate logic 1 state at the probe
tip.