David Navone - Navone Engineering
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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. The N-67 was designed to turn a small positive or negative spike into a longer pulse, up to around 30 seconds in length.

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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