Detection Circuit Description

The detection circuits consist of inputs Jl, J2, and J3, which sense an intrusion and energize P5, enabling timer IC2. A reset switch (S4) enables the circuit to be reset. A test switch (S5) enables the verification of system operation. Detection circuit functioning, along with the appropriate jack identification, is shown in Figure 28-3.

Construction

To begin assembling the project, follow these steps:

1. Lay out and identify all the parts and pieces to the assembly board (see Figure 28-4), sense board (refer to Figure 28-3), and the remain­ing parts for the final assembly.

2. Assemble inductor LI as shown later in Fig­ure 28-8. Drill a small hole in the bobbin for the stan of the winding and wrap 50 turns of #24 magnet-enameled wire tightly and evenly along the bobbin length. Tape the winding in place and allow 2 inches for both the “start” and ‘‘finish’* leads. Assemble everything as shown, inserting core halves into the bobbin, and place the air gap spacers between them

Detection Circuit Description

Figure 28-3 Defection circuit schematic

These spacers can be from a cut-up business card. You should attempt to find a thickness of 3 mils (.003) and confirm with vernier calipers. Tape the assembly together or use elastics, О-rings, and so on. The finished induc­tor should read approximately 1 millihenry when measured on an inductance capacitance bridge.

3. Create the heatsink bracket HS1 from a.75 X 2 X .0625 aluminum piece. Bend it 90 degrees in the middle and drill a hole for the SW1/NU1 screw and nut, as shown later in Figure 28-8.

4. Assemble the PCB as shown in Figure 28-4. Note the polarity of all the diodes, transistors, integrated circuit, and electrolytic capacitors. Note the two wire jumps. Be careful of the solder bridges on the PCB foil as these can cause damage to circuit components. Attach approximately 6 inches of wire leads to the front and rear panel-mounted components per Figures 28-4 and 28-5. Note that most resistors are vertically mounted. Always leave at least a ’/iб-inch lead between the body of the component and the board.

Experienced builders may use a piece of.1- tnch grid perforated vector board. Use Figure 28-4 for parts location and the schematic for the connections. Certain leads of the actual components will be used for connecting points and circuit runs. Do not cut or trim them at this time. It is best to temporarily fold the leads over to secure the individual parts from falling out of the board holes. If you obtain a PCB, you may omit this step. Figure 28-6 shows the foil layout.

5. Assemble a sense board from a piece of 2 lU – X 1 72-inch of Л-inch grid perforated board per Figure 28-7.

Insert the components into the board holes as shown. Certain leads are used for connecting points and circuit runs. Do not cut anything at this time. Fold over the leads to secure the parts in place.

Please read the following before doing any soldering:

a. Components are mounted both horizontally and vertically. Leave at least l/in of an inch between the part and the board surface.

Detection Circuit Description

Figure 28-4 Printed circuit board (PCB) wiring first level

b. Verify the polarity of ІСЗ, IC4, D1, D2, and D3.

Use a good, pencil-type soldering iron, keep­ing the tip tinned and cleaned. Use rosin core solder. Do not overheat the solder joint as you may damage a component. All the connec­tions should be smooth and shiny. Avoid excess solder.

Wire as shown, using the dashed lines as the circuit runs.

6. Attach the wire leads to the related front and rear panel components as shown.

Connect the interconnecting leads with the circuit board (see Figure 28-4) for P2. AUX12V, and P5, SHUTDOWN.

Note that most of these interconnecting leads are approximately 6 inches in length

7. Wire L2A. L2B, R17A, and R17B to the rear of transducers TD1 through 4, as shown in Figure 28-8. Note securing the two-conductor speaker leads is, done via a small nylon clamp.

8. Check the wiring for accuracy, correct compo­nents, the quality of the solder joints, short cir­cuits, foil shorts on the circuit board, pinched wires, and debris.

Final Rssembly

To complete the assembly, follow these steps:

1. Fabricate the chassis from a piece of 6- x 7- x .063-inch aluminum, as shown in Figure 28-8. Bend up 1 ‘/2-inch sections for the front and rear panels. Then bend up ‘/2-inch flanges to mount the cover via four sheet metal screws (SW2).The location ot most ot the mounting holes is not critical and may be “eyeballed.”

However, the holes for R2 and R9 should be measured to match the PCI PCB pads.

Detection Circuit Description

Figure 28-5 PCB wiring second level

2. Fabricate the cover from a piece of 8V2 – x 5- X Vi6-ineh-thick plastic or aluminum. Form it to fit over the chassis and secure it via mating holes for the SW2 serews.

3. Fabricate a 44л – X 3’/2-inch piece of plastic or cardboard insulating material for placement between the circuit boards and the metal chassis.

4. Finally, assemble the circuit boards and the panel-mounted components to the chassis as shown in Figures 28-4 and 28-5. Twist the leads and dress as shown. Use a small piece of sticky tape to hold them in place.

Test Procedure

Testing the device can be done by following these steps:

1. Insert a 1 – amp fuse into Fl, connect a shorting plug into J3, as shown in Figure 28-9, preset controls to full counterclockwise (CCW), and click “off.”

2. Apply 12 volts to the DC jack from a bench supply. You may useTl or a 1-amp wall adapter if a supply is not available.

3. Connect a scope to pin 3 of IC2. Turn on R9 and note a square wave, as shown in Figure 28-2. Rotate R9 a full clockwise (CW) turn

Detection Circuit Description

Figure 28-Б View offoil routing and pad location

Testing Detector-Sensing Circuit

To test the detector circuit, follow these steps:

1. Momentarily press S4 (RESET) and the unit shuts down. Press S5 (TEST) and the unit turns on. Repeat this action several times to verify proper operation.

2. With the unit in the reset mode, temporarily remove the shorting plug from J3 and note the unit turning on.

3. In the reset mode, temporarily short J2 to

and adjust RIO for a period of 50 microsec­onds (usee). This sels Ihe high-frequency range to 20 kHz.

Obtain hearing protection for the next steps.

4. Temporarily connect the four-transducer assemblies in parallel and connect to J6.Tum RIO a full CCW turn and note a piercing, shrill, and uncomfortable shriek. Adjust RIO CW and note the pitch increasing to an upper – frequency limit.

5. Turn on R2 and note the frequency of the shriek periodically changing. Adjust and note a sweeping action varying from very slow all the way lo a chirping sound.

ground and note the unit turning on.

Detection Circuit Description

Figure 28-7 Sense board layout and wiring

Still in Ihe reset mode, temporarily connect a 5-volt level to J1 and note ihe unit turning on.

Special Notes

The transducers used in this system are piezoelectric and consequently are many times more efficient than the electromagnetic type. Several operational curves and charts are available and intended for those who may want to modify or optimize the existing circuitry tor a particular range of frequencies, beam spread, and placement.

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