Monthly Archives: September 2014

Rssembly of a Field – ULIorthy, Integrated System

The laser receiver innards are placed inside a sturdy housing and secured in place. An adapter fitting is secured to the exit end, allowing the fitting of your choice of telephoto lens. The laser transmitter is housed with a collimator and is secured to the laser receiver by two aluminum brackets, rhis assembly requires good accuracy for main­taining close optical alignment, as any adjustment is via two micro-head adjusting screws for azimuth and elevation adjustments for fine-tuning.

You will note that the laser module is supported at its midsection by two rubber О-rings that provide a flexing motion both fore and aft. Compression springs are placed directly opposite the contact points of the micro-head adjusting screws. These springs load the position of the laser module beyond the optical alignment point and now require contact pressure of the micro head adjusting screws to adjust back into alignment against the spring pressure. The front points provide pivoting for elevation adjust­ments. whereas the rear points provide for the azimuth adjust.

Figure 13-16 Suggested system assembly—front view minus optics


Rssembly of a Field - ULIorthy, Integrated System

Parts and Fabrication Description

You must supply the following parts for final enclo­sure and assembly. Note that the recommended hous­ing is aluminum tubing with at least a ‘A-inch wall

thickness. Plastic PVC may be used for easier fabri­cating at the cost of mechanical stability.

• Main enclosure 23/« OD X l/4-inch wall alu­minum tubing. Fabricate a hole for the press fit of the handle section. Note l/4-20 holes for mounting to tripods.

Laser enclosure P/4 OD X 1/a – inch wall alu­minum tubing. Fabricate as shown for spring- retaining cutouts and holes for micro-adjusting verniers.

Rssembly of a Field - ULIorthy, Integrated System

Figure 13-17 Suggested system assembly—x-ray view of side

Handle l5/s-inch aluminum tubing for han­dle and battery enclosure.

Brackets Fabricate two brackets for securing the laser and main enclosure together. It is important that this step be as precise as possi­ble. as the two-enclosure axis must be parallel.

Control panel You may use the front panel of the laser receiver module. Fabricate additional holes for the test-tone switch and feed-through bushing for the cablc going to the laser section.

Rear panel For the rear section of the laser enclosure with a hole for cable bushing.

Lens mount adapter Fabricate for a ‘/2-inch – thick piece of PVC to fit into the innerdiame – ter (ID) of the main enclosure tube. Cut out

the center to mate with the telephoto lens of choice.

О-rings For sleeving over the laser module and sandwiching with the laser enclosure tube. The position along the length may be adjusted for besi movement using vernier adjusters. Experiment tor best results.

Springs Compression springs for maintaining a positive pressure against micro-adjusting vernier screws through their adjusting movement.

Micro-head adjusting screws For precise ele­vation and azimuth positioning.

Cable A multiconductor for 6-volt battery power and test-tone input to the laser module.

Switches For power and test-tone control to the laser module.

6-volt battery Uses a four AA battery pack for powering the laser module and is con­trolled by one of the switches.

• 9-volt battery For powering the test-tone cir­cuit.

• Telephoto lens An optional choice will greatly determine the potential range and per­formance of the system. Mates to the mount adapter.

• Cap Slip-on plastic cap for the retaining end of the handle.

* Cushioned headset with individual volume controls

Rssembly of a Field - ULIorthy, Integrated System

Table 13-1 Laser receiver parts list

Ref. #





10-ohm, ‘/4-watl resistor (brn-blk-blk)

R2,3,8,12,13, 15.16,17.18


І00К, ‘A-walt resistor (brn-blk-yel)



IK. ‘/4-watt resistor (brn-blk-red)


10K. ‘/4-watt resistor (brn-blk-or)


2.2K, ‘/4-watt resistor (red-red-red)



150K, ‘/4-watt resistor (br-grn-yel)



3 meg, ‘/4-watt resistor (or-blk-grn)


5K trimpot resistor


10K pot and switch



100 mfd/25 vertical electrolytic capacitor



1 mfd. 25-volt disc capacitor (104)



47 mfd/2f>-volt vertical, electrolytic capacitor

C8, Ю. 13


01/25-vnlt disc capacitor (1U3)


470 pfd. 25-vnlt disc capacitor (471)

Cll, 12


.001 mfd, 25-volt disc capacitor (102)


LM074 or 324 l4-pin DIP note


LM386 B8 pin DIP


Stereo jack for P1


9-volt battery clip


L14G3 phototransistor


1R light-emitter diode




2Ve-inch plastic cap


2-inch plastic cap


63A-inch X 24/n-inch sked 40 PVC tube


High-quality headsets


3- x 2-inch schedule 40 PVC (see Figure 13-13)


45- X 89-millimeter convex lens


2-inch plastic cap #A2 (see Figure 13-13)


Table 13-2 Laser transmitter parts list

Fief. #




Rl 5


100-ohm, !/4-watt (br-blk-br) resislor


470-ohm, ‘A-watt (yel-pur-br) resistor



27-ohm. 4t watt (red-pur-blk) resistor


5,000-ohm trimpot resistor 502



IK, !/4-watt (br-blk-red) resistor


5.6 m, lA-watt (gr-bl-gr) resislor

Cl 7


.01 mfd/50-volt disc capacitor


Ю mfd/25-volt vertical electrolytic capacitor



1 mfd/25-volt vertical electrolytic capacitor


3-voll zener diode 1N5221B



PN2907 PNPT092 transistor



PN2222 NPN T092 transistor


Any high-brighlness LED


Four-pin transistor socket


Four AA cell holder


Baitery clip


Small toggle switch; key or push butlon may be used


#24 bus wire for extension leads of SOCK1


12-inch #22 vinyl hookup wire





Laser diode with integrated optics



10-milliwatt, 880 rm laser diode; see text



Special fabricated aluminum heatsink, lens holder, and hardware



Basic lens in threaded fitting for 9-millimeter diode



15- X -25-millimeter double concave D( ‘V negative glass lens



24- X 75-millimeter double convex DCX glass lens



1- x ‘/№- wall X 7-inch length of clear polycarbonate tubing


835- X.6- X 2-inch length of schedule 401/’ inches PVC tubing


l/2-inch sked 40 female slip to male thread GENOVA 30405


‘/2-inch sked 40 female slip lo female thread GENOVA 30305


1-inch plastic cap


6-32 X 1/г-inch nylon screw


Labels cert, class, and aperture

System Application, Safety, and Legality

These fully working modules may be packaged by the builder into a compatible housing that will allow micro-mechanical adjustments. You can use a visible red laser module for short-range demonstration or sighting and alignment purposes, The illuminating laser transmitter must be precisely in alignment with the optical axis of the laser receiver and be mechani­cally fine-tuned via micrometer head screws to receive and process the scattered reflections. The laser transmitter described in this project uses the test-tone circuit that greatly simplifies rough optical alignment to a far-field surface. Output of the laser transmitter may be preset to 2 to 4 milliwatts for class 3a or at 8 to 10 milliwatts for class 3b. A collimator is included that greatly extends the potential range of the system. Optional use of the telephoto lens retro­fitted to the optical receiver will greatly enhance dis­tance and performance. The prebuilt modules may be set on tripods to verify performance integrity or for demonstration purposes before being enclosed.

The lasers used can be class 3a to class 3b visible or invisible. Protective eyewear is positively required in case you look into the dircct reflection. Using the scattered reflection mode is less dangerous.

Get permission of those parties you are listening to! Experimental demonstration of this system should not pose a legal problem, nor should it be used for applications not involving oral interception.

Setup Using Direct Reflection

The direct reflection method requires the following


Bill of Materials

R1 1K1/4 W (BR-BLK-RED)

R2 (1) 390K 1/4 W (OR-WH-YEL)

C1 (1) 100 M / 25V vert electro capacitor

C2 (1) 1 M / 25V vert electro capacitor

C3,4 (2) -01 M / 50V disc (103)

И з.

11 (1)555 DIP timer IC

S2 (1) Slider SPDT switch

CL1 (1) Battery snap clip

Test tone output

to a laser


Assembly board layout

WR1 (30") #24 vinyl hookup wire PB1 (1) 1 X 1.5” .1 grid perf board

System Application, Safety, and Legality

Figure 13-14 Test-tone circuit

System Application, Safety, and Legality

1. Obtain two video camera tripods and secure the laser transmitter to one and the laser receiver to the other. Use duct tape, bungee cord, electrical tape, and your own ingenuity.

2. Remove the rear cover of the laser receiver and install a 9-volt battery into the clip.

3. Determine the target window. Select an easy one that is nearly “normal” and on the same

level where you are located. Place a loud radio on the opposite side of the window.

4. If your laser is a pointer or gun sight, it will be

necessary to apply pressure to the trigger switch. This can be accomplished using a paper clip or clothespin to clamp the switch.

5. Position the laser transmitter tripod so the angle is as close as possible to the normal, reflected surface. This will allow minimal sep­aration between the transmitter and receiver.

Note that this is not necessary for proper per­formance hut is easier until you are familiar with overall system alignment.

6. Locate the position of the reflected “laser spot” resulting from the direct reflection of the laser beam as it bounces back from the window. This will depend a lot on the relative position as in step 5, since the angle of reflec­tion will equal the angle of incidence (Snell’s Law).

7. Carefully adjust the positioning of the laser receiver so that it intercepts the spot from the direct reflection. The final position where the reflected signal is incident on the phototran – sistor as viewed through the view hole.

8. If you are using the extender focal lens, adjust it so that the reflected signal is about the size of a penny as viewed on the phototransistor and the white baffled disc. This lens is not nec­essary for ranges below 50 feet.

9. Tiirn the amplifier on via the control and adjusl tl to a comfortable audio level. Opti­mum results may require “tweaking” to an actual signal. A rough adjustment requires detecting a weak optical signal source in total darkness and adjusting for the best perform­ance/noise figure. Note that the unit will not work correctly if not properly set.

10. Carefully adjust the position of the laser receiver for maximum clarity and volume. Note that only a slight adjustment can make a world of difference in performance. Experi­ment with the lens assembly when using ranges over 50 feet. Note the laser beam spot profile on the surface of the white baffle disc. You will see interference bands or fringes consisting of light and dark sections.

Note that clarity, volume, and general performance depend on many factors. The size of the window; the setting of the pane; and even the vibration picked up from window air conditioners, motors, pumps, oil burners, and so on can seriously degrade a usable signal.

Serious experimenters may want to interface the system with an audio equalizer to filter and enhance the usable signal. Again, experiment and experience is the best solution to quickly set up and obtain opti­mum performance.

A setup using the scattered reflection utilizes the light detected off the optical axis. The signal will be weaker over a given distance and will require more careful alignment.

You now have a choice of using the individual modules mounted on tripods for a demonstration of the concept and experiment. You may also choose to retrofit the modules within a sturdy housing similar to what is shown in the following data, providing a usable, field-worthy system of medium performance.

The objective is to allow an optical alignment between the laser impact point on the window and the return signal being coincident (coming back on same axis) to the optical axis of the receiver. Once this initial alignment is accomplished, it is only neces­sary to “tweak” the micro adjust screws that secure the laser optimizing the signal from any reasonable distance. It is assumed some signal is always detectable once initially aligned.

A test-tone signal modulates the laser at 1 to 2 kHz. This scheme provides easy access to aligning the optical axis. You now carefully search for the test tone, which is clearly detected with the optical receiver. Night vision equipment also can be an aid in initial alignment.

Mounting the laser in our test prototype involved floating it inside a stable housing, allowing several degrees of both vertical and horizontal adjustment for final “tweaking” using vernier adjust screws. The lens used on our prototype was from a low-cost video camera and screwed into a mating adapter plate firmly attached to the housing.

Obviously, a certain amount of mechanical ingenu­ity will be required in finalizing the system. The sug­gested assembly of this integrated system is shown in Figures 13-15.13-16, and 13-17.

Exact dimensions are not given, as this might limit you due to the access of materials and the use of your own ingenuity. We show our approach to be used only as a guide that may be closely or partially fol­lowed.

System Application, Safety, and Legality



Figure 13-15 Suggested system assembly—side view

Unit Is Ready for Pretest

To test the unit out, follow these steps:

1. Connect a headset to J1 and clip in a 9-volt battery or connect to a suitable DC bench supply. Preset R21 FCCW. Click on R22/S1 and advance until a hum is heard in the head­phones. Back off to a comfortable listening level. Note the hum is from the 60 Hz lighting.

2. Obtain a calculator with a clocked display and point unit to pick up the display emissions. Note a loud tone indicating signal pickup.

3. Verify the filter operation (which is not neces­sary unless circuit problems are encountered) by inserting a variable sine wave signal through an attenuator network across Q1. Preset the signal generator frequency to 1 kHz and turn up the level until a 1-volt peak- to-peak signal is measured via a scope con­nected across Jl. Slowly vary the signal frequency and note the output response. The signal should start to roll off at 300 H7 with 3 kHz peaking in the center of these extremes. The battery current should read approxi – mately 10 to 20 milliamperes with the head­phones connected, detecting a normal signal.

Final Assembly

гГЬс final steps are as follows:

I. Fabricate EN1. CAP1. and СAP2. as shown in Figure 13-11.

Unit Is Ready for Pretest

Unit Is Ready for Pretest

Place a dab of RTV or equivalent to secure BAF1 to printed circuit board. Verify position before adhesive sets.

Unit Is Ready for Pretest

Figure 13-12 Internal view of innards

Laser Receiver Is Ready for Final Testing

To conduct the final test, follow these steps;

1. Attach the unit to a video tripod via the 74-20 threaded hole.

Unit Is Ready for Pretest

Figure 13-13 Extender lens assembly

Unit Is Ready for Pretest

EXT 10 extender lens assembly

Lens retainer slides onto EXTUBE and secure lens. Remove 134" center section sim і liar to CAP 1 in Figure 13-10.

Unit Is Ready for Pretest

2. Obtain a source of signal such as the clocked display of a hand calculator or a similar device. Note the liquid crystal will not work. Point the unit in the general direction ot the display at a distance of 10 to 15 feet. Do not use the EXT 10 lens at this time.

3. Allow for total darkness and attempt to obtain a signal by panning the tripod. Adjust the bias light control R21 for the best signal to background noise. Note the difference in low – level signal detection in total darkness without the bias light.

4. Experiment with the EXTLO lens at longer distances and appreciate the detection sensi­tivity of this device. Note that alignment may be difficult due to a narrow field of view.

Laser Receiver

This section shows how to construct the electro-opti­cal receiver capable of detecting and reproducing the modulated information placed on optical beams of laser light energy. It also enables you to listen to any varying, periodic source of light, such as calculator displays, TV sets, normal lighting, the light produced from a fire, lightning, infrared sources, and of course intentionally modulated beams for voice or other analog communications. It functions as an excellent detector for this laser listening project by detecting the vibrations on a window or other similar surface when illuminated by laser light. These signals are clearly reproduced via a speaker or headset.

The device is housed in a round PVC enclosure that is easily mounted to a camera tripod when used

for sensitive positioning applications. The gain con­trol power switch and headphone jacks are mounted on the rear of the enclosure. A pistol grip configura­tion is suggested for pointing and listening to random sources.

Circuit Theory

Figure 13-8 shows the output from a sensitive photo – transistor (Ql) amplified by a low noise amplifier (I1D) to a gain of 50. The output is pass-band filtered by voice filter 11 ABC at 3-decibel rolloff points between 500 and 2,000 Hz. This provides maximum performance at most voice frequencies. The filtered output is further amplified to a usable level by IC2 for headsets or a small speaker. The J1 jack is connected to allow individual volume controls when using high- performance headsets (HS30). System gain is con­trolled via a pot and switch combination (R22/S1). SI controls battery (Bl) power to the circuit. A network consisting of resistors (R2 and R3) provides the nec­essary midpoint biasing for IIA BCD.

Lead from CL1

Laser Receiver

Laser Receiver

Magnified view showing J1 wiring schema.

Use a cut piece of lead wire from a component for this connection. Converts J1 to mono

Front view of R22 showing use of small pieces of wire from component cutoffs for connecting to pnnted circuit board Nole this is not

Figure I3-9 Optical receiver assembly board

Laser Receiver

Figure 13-Ю Assembly board layout foil traces

Construction 5tep5

To build the laser receiver, follow these steps:

1. Lay out and identify all the parts and pieces with the parts list—note the color identifica­tion on the resistors. Capacitors are easily identified by markings with alternative value codes in parentheses. Assembly is shown on a PCB with a foil layout, as shown in this data. Construction may be on a vector board if lay­out is followed

2. Insert the resistors as shown in Figure 13-9. Start with Rl and progress until all the resis­tors are mounted. Solder and clip off the excess leads. It is important lo avoid solder bridges, shorts, and cold solder joints. Figure 13-Ю shows the foil traces on the underside of the PCB for those wanting to etch their own.

3. Repeat with capacitors, observing the polarity of CI. C3, Сб. C7, and С14.

A special circuit consisting of LED1 provides a light bias to photolransislor Ql. This is especially use­ful in a low light signal condition when viewing the scattered reflection mode of operation. Resistor bias­ing Ql creates bothersome noise, limiting the full performance of the system. Trimpot R21 controls the emission output of LED1 and must be carefully adjusted in final testing for optimum effect.

4. Insen II and 12: note the position marks

5. Insert Ql phototransistor. Note the polarity as shown in Figure 13-7.

6. Insert B21, R22, and J1. Solder in placc.

7. Connect the CL1 battery clip. Note the color – coded leads and dedicated strain relief holes in the PCB.

8. Fabricate the baffle plate (BAFI), as shown in Figure 13-11. This piece is used to view the position of the reflected laser or focused light as gathered by the extender lens. It is neces­sary to position this light onto the lens of the phototransistor. The baffle should be small enough to slide into the enclosure tube with­out obstruction. Drill two small holes for the leads ol‘LED 1 and center the hole for the phototransistor. Insert the LED 1 leads, observing the polarity through the holes, and solder in place. Note the leads must be as long as possible. Position LED1 off to the side rela­tive to the Q1 phototransistor so the emission signal can obliquely be seen yet does not block out any signal along the optical axis. Position it as shown in Figure 13-12 and secure it to the PCB with an RTV adhesive or an equivalent.

9. Create SPCR1 from а І Чг – X 2-inch piece of plastic, cardboard, or any suitable resource. This picce is sandwiched between the battery and the bottom of the PC board for insulating

purposes, as shown in Figure 13-12. The bat­tery can simply be held in place with suitable elastic or an О-ring as shown. Create the colli­mator as shown in Figure 13-13.

10. Check all the wiring and the integrity of the solder points. Check tor solder bridges and shorts on the assembly circuit board.

Test-Tone Module Construction

To assemble the test-tone module, follow these steps:

1. Identify all parts and pieces and verify them with the bill of materials.

2. Insert the components, starting from one end of the perforated circuit board, and follow the locations shown later in Figure 13-14, using the individual holes as guides. The board is cut 1 X 1.5 x.1.

Use the leads of the actual components as the connection runs. These arc indicated by the

dashed lines. It is a good idea to trial-fii the larger parts before actually starting to solder.

Always avoid bare wire bridges, sloppy solder joints, and potential solder shorts. Check for cold or loose solder joints.

Pay attention to the polarity of the capacitors with polarity signs and all the semiconductors.

3. Cut. strip, and tin the wire leads for connect­ing to the diode laser module points X and Y. These should be #24 leads to fit into the hole pads of the laser module.

4. Connect a scope across output X and Y and connect a 9-volt battery to the CL1 snap clip. Note the circuit draws 10 milliamperes when activated.

5. Turn on SI and note a 1,000 to 1,500 Hz test tone of 2 volts peak.

6. Connect the output leads to the laser board, as shown at points X and Y. Preset the laser diode current to 100 milliamperes as directed Aim the laser at a light-colored surface. You

Figure 13-7 Final assembly view and labels

should clearly and loudly hear the test-tone signal when pointing the laser receiver in the direction of the scattered reflections.