HERE'S HOW ::. Series
Previous Here's How Issues
June 2003 (Part 1)
NAVONE ENGINEERING N-66A
for PULSE DOUBLING CIRCUIT
by Ron Mehlhaff
It was recently brought to my attention that some of
the newer vehicles require more than a single control
pulse in order to operate a particular accessory. For
instance, the automatic trunk release on some new cars
may require two positive pulses instead of the normal
single pulse. I would imagine that the second pulse is
for added safety. Anyway, this means that with most of
the present day alarm systems, you won't be able to
pop the trunk with the second remote button.
To solve this problem, I borrowed a couple of the
timing circuits made by Navone Engineering in
Stockton, CA (phone 800-669-6139). The N-67
is a Pulse Stretcher, based on a 555 timer, that has
five wires. The red wire is the supply +12 volts DC.
The black wire is the ground. The orange wire is the
output of the device, the green wire is the negative
trigger and the violet wire is the positive trigger.
We won't be using either trigger on the N-67.
was designed to turn a small positive or negative
spike into a longer pulse, up to around 30 seconds in
The Navone Engineering N-66a
is an adjustable delay circuit that only has three
wires. The input is the blue wire, the output is the
orange wire, and the black wire is the ground. The N-66a
works in this manner: When the +12 volt DC supply is
applied to the blue wire, the orange output lead
remains low (off) for up to 15 seconds. Then the
orange lead goes high (+12 volts DC) and remains high
until the supply is removed from the blue input.
Combining the Pulse Stretcher and the Delay Circuit
The goal of the circuit is to change a single negative
alarm triggered output pulse into a double positive
output pulse train. The normal duration of the
negative alarm output is usually less than one second.
The first pulse must come from the alarm itself. The
adjustment on the N-67
will alter the length of the second pulse. Don't
forget that it must be long enough to trigger the N-66a.
The adjustment on the N-66a
will alter the time between the two output pulses.
The wiring is straight forward, but I'd like to
mention that if you intend to operate the circuitry
with the engine running, then a suitable filter
capacitor should be connected across the supply. I
would recommend around 2200mfd at 16 volts DC. Also,
be sure to properly fuse all connections to the +12
volt DC supply.
You can test this circuit by simply grounding pin 86
of the first relay. Notice that when not in operation,
my circuitry draws very, very little current. For you
Bosch-type relay buffs, the +12 volt DC output of the
circuit comes from the Normally Open (pins 87)
contacts of either relay. Since the supply for the
relay's output comes from pin 30, through pin 87a
(normally closed contacts), and back into pin 30 of
the second relay, you can control many amps of current
with this circuit
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