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his laser is housed in a length of plastic electrical conduit which protects the laser tube and the high voltage power supply. To operate it, you press the pushbutton, just like a torch. You hold the button down to operate it, and take your finger off to stop. Simple. This conserves the batteries and reducesthe possibility of accidents. T Warnings Speaking of accidents, we need to stress a couple of safety points before we go to much further. (1). Looking directly into the laser tube while it is operating could damage your eyesight. The tubes used in this project are of low power, around a milliwatt or so, but they still could cause damage to your eyesight. So don't even think of looking into the tube while it is operating. Ever. (2). The power supply of this project is potentially LETHAL. Yes it could kill you, or at the very least, give you a very unpleasant electric shock. It may be battery powered but it contains a DC-to-DC inverter which steps the voltage up to very high levels. You can't even trust it when it is turned off, until it has had time for the capacitors to discharge. What is a laser? Lasers are becoming so commonplace now that it is easy to forget that they are using some pretty exotic technology. Laser stands for Light Ampli- fication by Stimulated Emission of Radiation. The important characteristics of lasers are that they produce very pure monochromatic light (ie, a single wavelength or frequency), that all the light waves are coherent (ie, in phase) and that the beam has very little divergence (ie, it is concentrated into a small spot). There are many different types of lasers. The first laser, demonstrated in July 1960 by Theodore Maiman, was a crystal laser (actually a rod of synthetic ruby with the ends finely ground and polished so that they were optically flat and exactly parallel to each other). Both the polished ends are silvered to act as mirrors but one is partially silvered so that some light passes through. This very precisely . Build this Battery Powered Laser Pointer By LEO SIMPSON Want to explore the fascinating technology of laser light? Now you can, with this battery powered laser. Completely portable, it could be used as a laser pointer for lectures or for laser experiments. 24 SILICON CHIP dimensioned ruby rod was resonant at one particular light frequency. All that it needed was some external stimulation and it would emit light at that particular frequency - see Fig.1. FULLY SILVERED END FLASH LAMP PARTIALLY SILVERED END LASER BEAM Pumping the laser Those early crystal lasers were stimulated or "pumped" by an external Xenon flash tube. They could not operate continuously, for two reasons. First, an Xenon flash tube will not operate continuously and secondly, a laser needs to dissipate a lot of heat when it is operating and crystals do not conduct or dissipate heat very well. Other types of lasers The most common types of laser are either gas or semiconductor. Gas and semiconductor lasers are not optically pumped but are stimulated or energised by passing a current through them. For gas lasers, this means a high voltage DC power supply is needed, capable of delivering many thousands of volts. Laser applications So what are some typical laser applications'? These days, you name it, it's got a laser in it. Well almost. The most common applications are in CD players and CD-ROM drives, in laser printers, and in barcode readers for supermarket checkouts and lending libraries. They're the everyday consumer applications but they also have lots of applications in industry, surveying, medicine and science. Now that lasers are so widespread, it is not surprising that low power laser tubes have become a great deal .l:.. Fig.1: the first laser was a synthetic ruby rod which was optically "pumped" by a high power Xenon discharge tube. By contrast, gas lasers are "pumped" by passing a current though the tube with a high voltage DC power supply. (Courtesy Radio-Electronics). cheaper in the last few years. Combine that fact with the use of other existing cheap technology and you can build a laser for not much more than $200.00. We're talking about a low power Helium-Neon laser, with a tube rated at 0.5-0.8 milliwatts or a slightly larger tube, rated at 1-1.SmW. The tube is energised from a 12-volt rechargeable battery pack via a DC-to-DC inverter. The whole lot - batteries, inverter and laser tube - is housed in a length of 40mm OD electrical conduit (in a nice bright orange colour) with suitable end pieces. Now let's have a look at the circuit which is shown in Fig.2. As will become more apparent when you look at the diagrams of Figs.3 & 4, the circuitry is in two parts: the transistor inverter and the rectifier circuit. Fluorescent light inverter Fig.2: the complete circuit of the laser. It is basically a small fluorescent light inverter driving a rectifier board to develop the high voltage. The two test points (TPl & TP2) are provided for checking the laser current (at 3.5 to 3.4mA). If necessary, the current is adjusted by changing the 68kQ and 33kn ballast resistors. With the supplied kits, this should not be necessary. The transistor inverter, built around Ql, Tl and Dl, is directly out of a battery powered fluorescent light. It comes already assembled on a miniature printed circuit board. Essentially, it is a "ringing choke" inverter. Transistor Ql oscillates by virtue of the positive feedback from the secondary of transformer T1 back to its base. It oscillates at about Z0kHz or so and steps the 12V DC input up to many r -- - - - - - - - - - -------7 SWITCHED~ _ _ _ _....,._ _ _ _ _ _ _ _ _ _ _ _ _ _ __ , • I , - - - - - - - - - - - - - ------7 I I LINK DIRECT~---' +1 0• 1JV .01 3kV 1M 0.25W 680pF 3kV J I 47 I' 1k 0.25W I I VOL 1~g\~,ml~LIER L ___ ____ __ _ I L _ _ __ _ _ _ _ _ _ _ _ DC-AC • SEE TEXT CONVERTER j ~ TP2 I ___ __ _ J LASER TUBE TP1 ECB DC POWERED LASER HEAD NOVEMBER 1990 25 TO LASER TUBE 10-14V +~ - 47~ Dl lA• l~ * SEE TEXT Fig.3: the wiring diagram for the two printed boards, showing also how they are linked together. Be sure to use the components specified since they operate at high voltage. [~ ....... !II ~I c:::,, z } ,.......--..... 12V NiCad BATTERY PACK I :9 ~ I------~ 1--- - - - -- - - - - - -- - - - ---JlOmm----- - - - - -- - - - - -- -~~ Fig.4: these "see through" diagrams shows how the laser and the battery pack are mounted in their respective lengths of electrical conduit. The endplates are made of 10mm-thick Perspex. hundreds of volts AC (depending on the loading). Normally the output of the transistor inverter would be fed to a small fluoresc ent tube (say around 8 to 10 watts rating) via the .0015µF capacitor from the transformer secondary winding. However, this circuit bypasses the .0015µF capacitor with a link to feed the rectifier circuit. Rectifier circuit There are two stages to the rectifier circuit. DZ and D3, together with two Close-up view of0.5-0.BmW laser tube, showing the 33kf2 2W ballast resistor wired to the positive electrode of the tube. 26 SILICON CHIP .0lµF capacitors, form a conventional halfwave voltage doubler circuit. Then, stacked on top of that is a Cockcroft-Walton voltage multiplier circuit comprising diodes D4, D5, D6 & D7 and their associated capacitors . When the circuit is firs t turned on, both the halfwave voltage doubler and the Cockcroft-Walton voltage multiplier work together to produce a voltage of between 3.5kV and 6kV to fire the laser tube and establish a discharge current of several milliamps through it. With the discharge current flow ing, the Cockcroft-Walton multiplier can no longer function prop erly because its high impedance is heavily loaded by the laser tube. This high internal impedance of the multiplier is artificially provided by the two 680pF high voltage capacitors and the 1MQ resistor. So what happens is that the halfwave voltage doub ler, DZ and D3, supp li es the laser tube via th e series path provided by th e diod es D4 to D7. Even so, th e voltage across the la- PARTS LIST Close-up view of the finished printed board assembly. The smaller board is from a portable fluorescent lamp and is su pplied ready assembled. 1 PC board, 78 x 26mm (for the rectifier circuit) 1 assembled fluorescent light inverter board (see text) 1 laser tube (see text) 1 304mm length of 40mm OD electrical conduit 1 184mm length of 40mm OD conduit 4 10mm th ick Perspex endplates to suit conduit 1 polarised male socket (2 or 4pin) 1 polarised female socket to suit male socket 12 small self-tapping screws to fasten endplates and polarised sockets 10 AA size nicad cells 1 pushbutton momentary contact switch 6 VG2X 2kV silicon diodes 3 .01 µF 3kV ceramic capacitors 2 680pF 3kV ceramic capacitors 1 1Mn 0.25W resistor 1 68kn SW wirewound resistor 1 33kn 2W resistor 1 1kn 0.25W resistor Miscellaneous Hookup wire , solder, etc. This view shows the completed assembly, ready for mounting in the electrical conduit. Remember that the circuit operates at high voltage so never touch any of the parts while power is applied. ser tube is still quite high, at close to 1000 vo lts DC. The current through th e tube is set by the "ballast res istors", a 68kn 5W and 33kn 2 watt type. And that 's just about it , as far as the circ ui t is con cerned. It runs from 12 volts DC as already ment ioned, provided by a "battery" of nicad ce lls or from an externa l 12 V battery. Construction This w hol e pro ject is avail ab le as a ki t from Oatl ey Electron ics so corn- ponent availability w ill not be a problem (see the panel on prices elsewhere in this article). As already noted, there are two PC boards, one of which (for the transistor inverter) w ill be supplied already assembled. All you have to do is fit two links to the board, although it is li ke ly that these, too, w ill already be fi tt ed . You w ill need to check your samp le board against the com ponent w iring d iagram of Fig.3 to confi rm thi s poin t. The rectifi er board takes 6 di odes, 6 capacito rs and 3 res istors. Note th at the diodes an d capacitors are far from ordinary in that they have high voltage ratings. The diodes are rated at 2kV w hile the ceramic disc capacitors are rated at 3kV. When assembling th is board, install the 6 diodes first , fo ll owed by the capacitors. Note that diode D3 hangs off the board slightly on one side, to clear one of the .0lµ F capacitors . The 1Mn resistor is mounted vertically, to save space. The 33kn 2W ballast resistor is not wired in at th is stage - that is done later wh en the circuit is co nnected to the laser tube. Wh en the rectifi er board is complete, it can be connected to the inverter board with two short links of tinned copper w ire. Th e d iagram of Fig.3 and the photos show how they go together. Initial tests By thi s time , you 'll probably be itc hing to do a test ru n an d yes, you can do so, prov ided yo u have a 12V NO\' f•:/1 1/lE/l 1990 27 laser tube are laid out on your workbench or table which must have a safe insulating surface. Connect the two input leads the battery and the laser tube should fire up immediately. If not, disconnect and leave the unit for a few minutes, to allow the high voltage capacitors to completely discharge. Remember, they can give you a substantial shock, even if no power is applied to the circuit. Once the capacitors have discharged, you can safely check your work and rectify any mistakes. Battery pack The laser & the two PC boards are simply slid into the electrical conduit. Note the special cutout for the pushbutton switch. Wrap the laser tube in a small piece of corrugated cardboard to centre it in the conduit & hold it in position. power supply which can deliver about an amp or so. Before you think about connecting the power supply though, the laser tube must be connected, together with the in-line 33kQ ZW ballast resistor. Notice that the laser tube is polarised. The negative electrode is the one connected to the internal metal shield. The negative wire from the rectifier board goes to the negative electrode. The positive wire, from the 5W resistor end of the rectifier board, connects to the positive electrode of the laser tube via the 33kQ ZW ballast resistor. That done , check all your work carefully. The unit is now ready for testing. Before you do that though, make sure that both boards and the The 12V battery pack is made up from 10 1.2V AA size cells. These are soldered in series, in two groups of four and one group of two, as shown in the battery pack diagram in Fig.4. These are then packed (squeezed tightly is probably a better description!) into a 184mm length of 40mm OD electrical conduit. The endplates are made of 10mm-thick Perspex, drilled to take small fixing screws. One of the end plates is drilled to take a polarised male socket for the DC connections. Before the batteries are finally inserted into the electrical conduit, a layer of card or other insulating material is placed between each group of cells, to avoid the possibility of shorts. Laser head As an alternative to the nicads, you can use a 12V sealed lead acid battery housed in a plastic case as shown here. This will give longer battery life than the nicads but the arrangement is not as convenient. 28 SILICON CHIP The laser tube and its driving circuitry are also mounted in a section of 40mm OD electrical conduit, 304mm long. This also has 10mmthick Perspex end plates. One of these, mounted at the laser tube end, has a 6mm hole drilled right through it, to avoid any obstruction of the laser light. The other end plate carries a female polarised socket, to match the one on the battery pack. A hole needs to be cut for the pushbutton switch 100mm from one ertd of the conduit. The switch is a pushfit into a specially shaped cutout, roughly 13mm by 12mm. You'll need to do it by drilling the outline and then finishing with a small rectangular file. The laser tube and the accompanying printed boards are a comfortable fit into the conduit. Before they are inserted though, you'll need to pack some pliant insulating material, such as pieces of corrugated cardboard, around the laser tube so that it is Thia computer and electronic game Joyaliclr la c/4WJt1y t»algned for two handad oparalion. Th/a not only helf» to lncre- control and accuracy but a/ao prolong• playing tin» by reducing hand fatigue that can be auociaflHI with nonnal eing/a hand operated unlla. The JSC-5 la e/ao t»elgned .a the handgripe can eaeily be reated on a fable or olhH flat ~~:::;..' eurfece for .,abilizing the unit during uee. It la compatible with moat computera Including -.-+-,,Ametrad, Atari, Commodore •nd ~ E LECTRONICS SOUND AUSTRALIA Your P.A. Accessory Specialist The end plates for the plastic conduit are made from lOmm-thick Perspex, drilled to take small fixing screws. This particular end plate carries the polarised DC power socket. centrally located in the conduit. Next, the wires for the switch are fed through the conduit and out through the switch hole. The wires are soldered to the switch and then the laser tube and the PC boards are installed in the conduit. The DC input wires are soldered to the polarised female socket and the two endplates are fitted. Finally, the laser head and the battery pack are fitted together by a standard double female plastic fitting which has an internal diameter of 40mm - a snug fit over the conduit. Now plug the two units together, push the switch and your Laser Pointer STEEL SPEAKER GRILLES CHROME CATCHES 5'· $ 8.95 6"- $ 9.95 Large Lockable $9.95 8'- $11.95 10' - $15.95 Small Lockable $4.95 12'- $19.95 15"- $23.95 STEEL SPEAKER 18"- $34.95 Clamps for GRILLES Grilles Pk4- $2.95 5' $8.95 STEEL DISHES Suit 1 x Male XLR + Female XLR $4.95 As above also 2 x 1/4" Sockets Suit 2 x 1/4' Sockets PLASTIC DISHES Suit 2 X 1/4' Sockets $3.95 $5.95 $4.95 PLASTIC CORNERS Large Corner/Foot$2.95 Large Stackable$2.95 Large lnterlocking$1.95 Medium lnterlocking$2.95 Extrusion for above $5.95/M 6' Strap $ 1.95 8' Strap 10· Strap $ 4.95 8' Nylon Briefcase Style Chest Handle Metal Recessed Spring Handle $ 2.45 $ 2.95 $ 2.95 $ 5.95 $12.95 HEAVY DUTY CARPETED ROAD CASES 4 Unit $100 .00 6 Unit $115.00 8 Unit $135.00 10 Unit $155.00 12 Unit $175.00 This photo shows how the AA nicad cells are shoe-horned into the electrical conduit. Rack Cases can be made to order in any size and any colour carpet. MICROPHONE WINDSHIELDS BLACK, YELLOW, REO , BLUE, ORANGE ALL $5.50ea RACK HANDLES. GOOSE NECKS, CABLES. CONNECTORS and lots more available Please Call for a Catalogue SOUND AUSTRALIA 28 Walker S~. Dandenong, VIC, 3175 Telephone: (03) 791 1622 Where to get the kit Kits tor this project are available from Oatley Electronics. The complete kit for the laser head, including a 0.5-0.8mW tube, is $189.00. With a 1-1.5mW tube, the price is $209.00. The battery pack is $29.90. Certified postage and packing for the above items is $8.00. Also available is a 12V 6.5A.h sealed lead acid battery for $27.90. You can contact Oatley Electronics by phone on (02) 579 4985 or by post at PO Box 89, Oatley, NSW 2223. At Last!!! Public Address & 11 ,It1 Hi Fi Combined Ill This is the business end of the laser, showing the Perspex end plate with a hole drilled though it. should "laze" away. Have fun but remember our warnings about looking into the laser tube while it is operating. Remember too that the circuit operates at high voltages and that some of the capacitors can remain charged for quite some time after the power is turned off. ~ It t\ . 'I Now you can havw Hi R qulllity audio anywhe,.., The SP352L T -,,.llkera haw, their own on board 100 \'OIi IIM x'forme,.. to Ol!WrC~ long, crowded cab/a ruM. Theee speaker• can be connected up to eny 700 11011 line output on moet mono public •ddratul amp/lW.,.. If true etereo ie required they can ew,n be hooked up to a domealic Hi R amplifier with the aid of euy to lnela/1 step up tranefonnera. lt»al for office and warehouee eetupe or even if you llimp/y want H R audio piped through to your ewimming pool and backyard. The SP352L re ere t»eigned around a high Impact black cabinet with ~ I, mete/ n»eh gr/I,. and coma ELECTRONICS with mounting bracketa. I' ' ''. 'l .aD Tl.'1111\. ft NOVEMBER 1990 29