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BUILD YOUR OWN LASER LIGHTSHOW You’ve seen those fancy lightshows at discos and pop concerts. Now you can build your own using an exotic blue Argon laser or you can save money and use a Helium-Neon laser instead. The lightshow is provided by a motor-driven mirror system con­trolled with simple electronic circuitry. Design by BRANCO JUSTIC May 1996  57 The interior of the helium-neon laser lightshow includes the tube itself, the high voltage power supply and the three motor mirror deflection system W HILE LASERS ARE widely used in industry and entertainment, they still have a capacity to fascinate. And they are all the more fascinating when they are deflected into myriad patterns by a motor drive system. Combine the motor drive system with a fog machine and you can have some really interesting effects, espe­cially if a blue argon laser is used. In essence, the lightshow presented here can be used with any visible laser. Well, that’s not quite true because if the laser was a high-power unit, the The exterior of the helium-neon laser lightshow is covered in grey carpet to provide a surface finish which stands up well to disco use. 58  Silicon Chip deflection mirrors would be cooked but since few readers will have the budget for a high-power laser we won’t worry too much. The photo at the start of this article shows only one of the endless number of patterns produced by this lightshow. The patterns vary from single to multiple flowers, collapsing cir­cles, rotating single and multiple ellipses, stars and so on. We are presenting two lasers in this article. The first, the 100 milliwatt (100mW) argon unit referred to above, can be purchased virtually ready to run. It needs to be hooked up to a beefy power supply and housed in a substantial carrying box, along with the motor deflection system. It also requires forced air cooling. The circuit is shown in Fig.1. The second unit is a 10mW helium-neon laser and it too is available as a ready-to-run unit needing only a suitable power supply and a box. As presented here, the motor deflection system has three motors although it could use two or four. Each motor can run at eight different speeds and one of the motors is periodically re­ versed while another is stopped for varying intervals. The specified motor is a DC type with four wires, two for the armature and two for feedback, for precise speed control. The motor drive circuit is shown in Fig.2. This shows the complete circuitry for two motors and employs an LM358 dual op amp. Circuit details Let’s describe the circuit involving op amp IC1a and tran­sistor Q1. Q1 is a BD679 Darlington transistor which drives the motor with varying DC. Q1 Fig.1: this diagram shows the power supply of an Argon gas laser. Fig.2: this dual motor control circuit employs the feedback winding of the motor to give precise speed control. It’s based on an LM358 dual op amp (IC1a & IC1b). May 1996  59 60  Silicon Chip Fig.3 (facing page): this driver circuit provides eight different voltage settings to inputs A & B on Fig.2. It also provides reversing of one motor via relay RLY1 and periodic stopping of another motor via relay RLY2. is driven by op amp IC1a which functions as an error amplifier. It compares the reference voltage at its pin 5 with the feedback voltage (derived from the motor) at pin 6. If the feedback voltage is slightly low, then the op amp increases its output to Q1 and the motor. Similarly, if the feedback voltage is slightly higher, indicating a higher than desired motor speed, the op amp will reduce its output to Q1 and the motor. The feedback signal from the motor is fed to a diode pump rectifier consist- Fig.4: this is the power supply to drive the circuitry of Figs.1 & 2. ing of diodes D1 & D2, together with capacitors C1 & C2. This produces a DC voltage (V1) which is proportional to the speed of the motor. A table is included in the diagram of Fig.2, giving typical values of V1 for a range of DC voltages to the motor. VREF, the reference voltage applied to pin 5, is preset by trimpot VR1 and is derived from 6.2V zener diode ZD1. VREF is the basic speed setting for the motor but this is varied up and down by a voltage fed to point A. Point A is driven by the circuit of Fig.3, the Automatic Lightshow Driver. The circuit of Fig.3 is designed to Fig.5: this composite board layout includes all the circuitry of Fig.3 and two dual motor drivers, as shown in Fig.2. Note that while it could control four motors, only three are used in the lightshow. May 1996  61 This photo shows a finished composite PC board and the power supply. Note that the wiring between the various sections of the com­posite board does not agree with the wiring shown in Fig.7 although it is still valid. All three motors are speed controlled, one motor is periodically reversed by relay RLY1 and one motor is periodically stopped by relay RLY2. Fig.6: component layout for the power supply of Fig.4. This close-up photo shows the mirrors attached to the drive pulleys of the motors. Note that the wiring should be laced up neatly so that it cannot foul any of the rotating mirrors. 62  Silicon Chip randomly vary the speed of up to four motors via one or two “Dual Motor Speed Con­ trollers”, as depicted in Fig.2. Note that while it can control up to four motors, only three motors are used in the laser lightshow presented in this article. The circuit is based on IC1, a 4060 14-stage binary ripple counter with a built in oscillator. Its frequency of operation is determined by C1, R2 and R1 and is about 40kHz. It is gated on and off, via diode D1, by a low frequency oscillator based on IC2c, a 2-input NAND Schmitt trigger gate. When the output of IC2c is high, the 40kHz oscillator runs and when IC2c’s output is low, the oscillator is stopped. The running time is nominal- Fig.7: here are the inter-wiring details for the composite board of Fig.5. ly one while the stop time is about five times that, with VR1 at its minimum setting. When VR1 is at its maximum setting, the stop time is about eleven times longer. So the duty cycle of the 40kHz oscillator is variable by VR1 from about 5:1 to about 55:1. In practice, the run and stop times will depend more on the hysteresis of the 4093 Schmitt NAND gate than on the time-constants of R3.C2 and R4.C2. In our prototype, the run time was less than 70 milliseconds and the minimum stop time was about 0.35 seconds. The maximum stop time was about four seconds. These variations brought about by the 4093 are not important and do not affect the circuit operation. As the 40kHz oscillator is gated on an off, the ripple counter runs or stops as well. So its 14 outputs are changed, high or low, every few seconds in an apparently random fashion. 12 of these outputs are used to switch transistors Q1-Q12 on or off. The transistors are arranged in groups of three and because of the differing collector resistors and depending on how they are switched by the 4060, they will provide eight different voltages at points A & B on the motor speed controller boards. A LED is connected in series with each transistor base, giving an indication when the respective transistor is on. Stop & reverse Pin 4 of the 4060 is also used to drive transistor Q13 and its relay. This is used to periodically reverse the direction of one of the motors. At the same time, pin 15 is buffered by the three remaining gates in IC2 and these drive a second relay to periodi­ cally stop one of the motors. Both of these measures add to the variability of the patterns produced. Fig.4 is the circuit of the 12V power supply which feeds the circuits of Fig.2 and Fig.3 and the three motors. May 1996  63 Fig.8: suggested orientation of the three motors. It is powered by a 12V 1A plugpack transformer. Fig.4 comprises four diodes and a 1000µF capacitor driving a 7812 3-terminal 12V regulator. This is bypassed at its inputs and outputs with 10µF and .068µF capacitors. Construction As far as the construction details of this project are concerned, we will assume that you already have a complete laser which is working. To make it function as a lightshow you will need to build two PC boards, mount three motors on a board and wire them all together. The circuits of Fig.2 and Fig.3 have been made available as one PC board, which has two 2-motor drive circuits on it. The layout for this composite Lasers: Dangers & Warnings The following is an brief outline of dangers and warnings for all laser devices. For more detailed guidelines we recommend contacting the “Department of Health and Radiation” in Victoria for a copy of “Safety Guidelines For Lasers In Entertainment”. ● Lasers above a certain power level (eg, over 1mW) require licensing in some states. Check with your state government department. ● Never look into a laser beam. This will cause eye damage. ● The user must be aware of all potential dangers involved in the operation of the laser. ● Gas lasers (ie, argon and helium-neon) use very high voltage at 64  Silicon Chip very dangerous or lethal energy levels. Many tubes typically require over 10kV to strike and run continuously at around 2kV. ● Do not attempt to build a laser unless you are qualified to work with high voltage equipment. ● Never touch any part of the laser supply or tube while it is operating. ● Capacitors in laser supplies retain their high voltage for long periods after being switched off. Always discharge each high voltage capacitor after switching off when making repairs to the unit. ● Warning stickers relating to both laser light and high voltage must be attached to the laser (these are included in the kit). board is shown in Fig.5. Once again, note that only three motors are required but Fig.5 shows circui­try for four motors. You can leave the unwanted bits out but they only amount to a 6.2V zener diode, a BD679 transistor, a 10kΩ trimpot and a few resistors and capacitors. Assembling the composite board is quite straightforward. PC stakes should be provided for all the external wiring connec­tions. Make sure that all polarised components are inserted correctly. It is wise to check the polarity of at least one of the supplied LEDs because it is not unusual for these to be supplied with polarity reversed; ie, the longer lead is sometimes the cathode instead of the anode. Fig.6 shows the component layout for the PC board. We sug­gest that a larger heatsink be fitted to the regulator than the one shown in our photos. The regulator heatsink in our prototype ran a little too warm for our liking. When the power supply board is completed, it should be powered up and its output voltage checked – it should be close to +12V. Do this check before connecting its output to the composite board. Fig.7 shows how the composite board is wired. The operation of this board should be checked before the motors are connected. Apply power and check for the presence of +12V and +6.2V at all points shown on the circuits of Fig.2 and Fig.3. With power applied, all the LEDs should switch on and off at regular intervals and you should hear the relays click on and off as well. Provided all LEDs operate then the board is probably functioning correctly. It is now a matter of connecting the three motors. Before that is done, they need to have mirrors fitted onto their pul­leys. This is relatively simple, although some care should be taken to keep the angle as small as possible. If the angle is too large, the laser deflection will be excessive and it will be difficult to line it up to hit the successive mirror. Excessive laser deflection will also result in patterns that are too large and have reduced brightness. Each mirror should be secured with silicone caulking com­ pound which does not set hard. This will provide a degree of cushioning for the mirrors when the motors suddenly stop or reverse direction. Inside an Argon laser, showing the brute force power supply, squirrel cage fan for cooling and the three-motor mirror deflection system. Start by placing a square (2 x 2mm) piece of electrical tape onto the rim of the pulley. This will give a sufficient angle for the mirror. This done, apply a small amount of silicone compound to the pulley and attach the mirror firmly at the de­sired angle. Fig.8 shows how the motors should be positioned with re­spect to the laser beam. We suggest that the baseboard be made of HMR (high moisture resistant) particle board for long-term stability. Any other timber will tend to warp and throw the motors out of alignment. The motors can be simply attached to the baseboard base using hot melt glue. This will allow the construc­tor to align each motor as the glue sets. You will need to run the whole system together with a laser before the glue finally sets, to make sure that the SC alignment is satisfactory. Kit Availability Kits for the laser lightshow described in this article are available from Oatley Electronics who own the design copyright. They have kits for Argon and Helium-Neon lasers as well as the lightshow controller. The pricing details are as follows: Laser light show (does not include laser or its power supply) – includes all electronic components for PC boards and three motors and mirrors: $90.00. Suitable plugpack transformer: $14.00 He-Ne laser and power supply: $80-120, depending on tube rating. Laser case kit – includes 12V power supply, precut 16mm craftwood box, plastic corners, all screws and grey carpet: approximately $90 (ring for details and availability). Argon laser: $300-500, depending on hours of usage (ie, these are second­ hand tubes). Ring for details of availability and power supply requirements. For further information on pricing and availability, contact Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985 or fax (02) 570 7910. May 1996  65