Fullscreen HTML5Med Res (??MB)HTML4

Build your own LIGHTSHOW PART 1: By LEO SIMPSON & RICK WALTERS Whenever you go to hear your favourite band or disco, there is bound to be a light show. Now you can have your own, in your home, your car or virtually anywhere as this one runs on 12V AC or DC. 18  Silicon Chip T HIS IS NOT THE FIRST light show we have published. Our first was the highly successful DiscoLight published in the July & August 1988 issues of SILICON CHIP. Many thousands of Disco­Lights have been built over the years and they are standard equipment in many portable discos. They are still available as kits from Dick Smith Electronics and Altronics. This new Light Show has all the user features of the popu­lar DiscoLight but it operates from 12V DC or 12V AC and drives standard 20W or 50W halogen lamps. Like the DiscoLight, the Light Show drives four channels of coloured lights. It can be controlled directly from your stereo system’s loudspeakers or a portable CD player, or it can be trig­gered from live music picked up by an inbuilt microphone. It also has its own chaser functions so it can produce all sorts of light patterns on its own, with or without modulation by the music. Not only can the Light Show be used in your home but you could even use it in your car, caravan or recreational vehicle since it runs from a 12V battery, if you want. Think how it could boost the rating of your car in a “Sound Off” competition. What it does The Light Show divides the audio signal from your stereo system into four frequency bands to modulate the brightness of four halogen lamps. Each lamp shines through a coloured filter, to make an eye-catching display. You might use red for the lowest frequency band, then green, yellow and blue for the highest frequency band. When the music stops, the Light Show can be switched to provide its own light patterns: chaser, strobe and alternate patterns (we’ll describe these later). Let’s have a look at some of the features of the Light Show. On the rear panel is a two-way insulated terminal block for the 12V input and a fuseholder. Another five-way insulated termi­nal block is provided for connection of four 20W or 50W halogen lamps. There is also a set of four spring-loaded terminals so that you can connect the signals from both channels of your stereo amplifier (or portable CD player, Walkman or other program source). These are connected Main Features Operating features •  Four light channels controlled by four separate audio channels •  Forward, reverse and auto-reversing chaser patterns •  Simultaneous strobe on all four channels •  Alternate light mode •  Music modulation available on chaser, strobe and alternate modes •  Adjustable rate for chaser, strobe and alternate modes •  Inbuilt microphone for beat triggering or audio modulation of lights •  Direct inputs for beat triggering or audio modulation of lights •  Sensitivity control •  Internal presettable sensitivity levels for each channel •  Front panel LEDs mimic light display Electrical features •  Operates from 12V DC or 12V AC •  400W maximum lamp load •  100W maximum lamp load in each channel •  Fused supply to lamps in parallel with your loudspeakers and cause negligible loading of your amplifier’s outputs. On the front panel are two knobs, a power switch and a group of five toggle switches, three of which are 3-position types. There are also five LEDs, one to indicate it is ON while the other four LEDs show what’s happening in each of the four channels. Let’s look at the functions of the group of five toggle switches first. Right next to the SPEED knob is the INPUT switch and this selects either the internal electret microphone or an external source which will normally be your stereo amplifier outputs. If the Light Show is being used near a live band (or a loud amplifi­er) you can merely switch to microphone and eliminate the need for any cable connections. As you might expect, you can use the LEVEL knob to adjust the audio signal level for the best light display. In the centre of the five toggles is the DISPLAY switch. This 3-position switch is the key to the Light Show’s functions. In its top DISCO position, you get the basic Light Show function whereby the audio signal is split into four separate frequency bands (low bass, upper bass, mid-treble and upper treble) and each of these bands control their respective lights. The brightness of the lamps at any instant is directly proportional to the sound level in the respective audio frequency band. In the Modulate (MOD) position of the DISPLAY switch, the audio signal both modulates the lights and triggers the various modes selected by the adjacent PATTERN switch. Finally, the Unmodulated (UNMOD) setting of the DISPLAY switch allows the light display to be set by the PATTERN switch. The PATTERN switch gives three light displays: 4-light chaser, strobe and alternate. The Chaser mode is self explana­tory; the four lights chase each other in one direction or the other, as set by the adjacent DIRECTION switch. The speed at which the lights chase each other is set by the SPEED control knob. In the Strobe mode, all four lights flash on simultaneous­ly, at a rate set by the SPEED control. In the Alternate mode, two pairs of lights flash on and off alternately, again, at a rate set by the SPEED control. The DIRECTION switch controls the Chaser mode. You can have the lamps chase in one direction or the other or change direction automatically, every minute or so. Finally, the BEAT switch gives beat triggering from the music for the Chaser, Strobe and Alternate pattern modes. In the Oscillator setting of the BEAT switch, these functions are January 1998  19 Fig.1: the audio signal is split into four frequency bands, rectified and compared with a 50Hz ramp reference signal. The Mosfets are then switched either by the comparator outputs or by signals from the inbuilt pattern generator. con­trolled by the SPEED knob. The four LEDs on the front panel mimic the behaviour of the four light channels, so that even if you can’t see the lamps directly (say you are acting as disco operator), you can tell what they are doing by looking at the LEDs. The LEDs also come in handy during any troubleshooting which may have to be done and they also allow all the circuit functions to be tested without connecting the lamps. How it works The circuitry for the Light Show consists of three quad op amp ICs, five CMOS ICs, four power Mosfets, five LEDs, one 3-terminal regulator and 19 diodes. And that’s just the semis. Add in the resistors, capacitors, switches, pots and all the other hardware bits and it comes to quite a stack of components. Fig.1 shows the block diagram of the circuit. Switch S1 selects the audio signal, either from the internal microphone or from the loudspeaker terminals (which connect to your stereo). The audio signal is then fed to four filters which split it into four 20  Silicon Chip distinct frequency bands: Low Bass, Upper Bass, Mid Treble and Upper Treble. The Low Bass frequency band is provided by a 200Hz low pass filter – this means that only signal frequencies below 200Hz are allowed to pass. Then there is the Upper Bass band which passes a band of frequencies centred on about 440Hz. This is actually a narrow bandpass filter centred on 440Hz. The Mid Treble band is another bandpass filter, centred on 1kHz. Finally, the Upper Treble band is from 2kHz to 20kHz and is provided by a 2kHz high pass filter (ie, everything above 2kHz passes). Fig.2 shows the response of all the filter bands. As you can see, the whole audio band is not treated equally, in that some frequencies around 300Hz, 600-700Hz and 1.5kHz are somewhat attenuated but that does not matter in the overall scheme of things. The audio signal from each of the four filters is rectified and smoothed to provide a varying DC level, which is then fed to one of four comparators. The comparators compare the varying DC signal to a 50Hz ramp reference signal which is derived from the pulse generator and shaper. Fig.3 shows the interaction of the varying DC, from one of the audio filters and rectifiers, with the 50Hz ramp reference signal. Whenever the slowly varying DC signal is above the level of the 50Hz reference signal, the output of the comparator goes high to turn on the associated Mosfet. That’s the basic process of how the audio signal is filtered and rectified and then used to control the Mosfet switching time to vary the re­spective lamp’s brightness. But as you might have guessed, there’s a lot more to it than that, otherwise the circuit of the Light Show (which you’ve probably looked at and shuddered) would be a lot simpler. Now refer back to Fig.1. Instead of the four comparator outputs going directly to trigger the Mosfets they go via a block labelled as a 4-pole double throw switch (IC5). This switching IC selects either the signals from the four comparators or a pattern generator. Signals from the pattern generator drive the Mosfets and hence the lamps in the chaser, strobe or alternate modes. Well, that’s probably as far as we can go with block dia­grams in describing the basic operation of the Light Show. Now, we have to stop dithering about and get into the circuit descrip­tion proper. Circuit description Let’s start at the extreme top lefthand corner of circuit of Fig.4. Op amp IC1b provides gain for the electret microphone. The electret is powered via a network consisting of a 1kΩ resis­ tor and 100µF capacitor which provide decoupling from the main +10V supply while bias current is fed via the 4.7kΩ resistor. The electret’s signal is coupled by a .047µF capacitor to the non-inverting (+) input of IC1b which boosts the signal by about 31 times. The output of IC1b is coupled via a .047µF capacitor to the INPUT switch S1. Also connected to this switch is an input atten­uator consisting of two 10kΩ resistors, one for each speaker lead from your stereo amplifier. The 10kΩ resistors connect via a common 1.8kΩ resistor to ground. This networks mixes the two stereo channels together as well as attenuating them. After INPUT switch S1, the signal is fed to the LEVEL con­trol (VR5) and then to op amp IC1a (a stage identical to IC1b) which again provides a gain of 31 times. IC1a’s output is then fed to the four filter stages to provide the four frequency bands mentioned previously. IC2d and its associated components form the 2kHz high pass filter. This is a third order (three RC time-constants) filter which means that signals below 2kHz are rolled off at 18dB/oc­tave. IC2c and associated components form the 200Hz low pass filter and again this is a third order type. IC2a and IC2b and their associated components form twin-T filters. These are the 440Hz and 1kHz bandpass filters for the upper-bass and mid-treble frequency bands (as shown on Fig.1). The output of each filter is rectified with a diode pump consisting of two diodes, a 10µF coupling capacitor and a 1µF smoothing capacitor. The varying DC output from each filter stage is fed to a 50kΩ preset potentiometer (VR1-VR4). Thus the sen­ sitivity of each channel can be set to provide equal brightness of the lamps for typical music signals. Following the presets, the DC signals are fed to the non-inverting inputs of op amps IC3a, IC3b, IC3c & IC3d which are wired as comparators. These compare the varying DC AUDIO PRECISION SCFREQRE AMPL(dBr) & AMPL(dBr) vs FREQ(Hz) 15.000 13 NOV 97 13:57:55 15.00 10.000 10.00 5.0000 5.000 0.0 0.0 -5.000 -5.00 -10.00 -10.0 T -15.00 20 100 1k T T T 10k -15.0 20k Fig.2: this plot shows the response of the four filter bands which drive the Mosfets. As you can see, the whole audio band is not treated equally, in that some frequencies around 300Hz, 600-700Hz and 1.5kHz are somewhat attenuated but that does not matter in the overall scheme of things. Fig.3: these digital scope waveforms show how the varying DC signal from one of the audio filters and rectifiers (middle trace) interacts with the 50Hz ramp reference signal (top trace). Whenever the slowly varying DC signal is above the level of the 50Hz reference signal, the output of the comparator (bottom trace) goes high to turn on the associated Mosfet. Fig.4 (following page): the complete circuit diagram of the Light Show. IC2a, b, c & d are the four audio filters which are followed by rectifiers which feed trimpots VR1, VR2, VR3 and VR4 and then IC3a, b, c & d which are the comparators. IC5 is the display selector while IC4b, IC6 & IC7 make up the pattern generator. January 1998  21 22  Silicon Chip January 1998  23 Parts List 1 main PC board, code 01112971, 234mm x 160mm 1 front panel PC board, code 01112972, 120mm x 50mm 1 plastic case, 260mm x 180mm x 65mm, complete with metal panels; Jaycar HB-5974 or equivalent 4 20W or 50W halogen lamps (see text) 4 halogen lamp sockets 1 12V 5.25A enclosed halogen lamp transformer; Jaycar MP-3050 or equivalent (AC operation; see text) 3 SPDT toggle switches (S1,S5, S6) 1 SP3T toggle switch (S2); Jaycar ST-0558 or equivalent 2 DP3T toggle switches (S3,S4) 5 bezels for 5mm LEDs 2 16-pin IDC headers, Jaycar PI-6550 or equivalent 1 150mm-length 16-way ribbon cable to suit header 1 electret microphone 1 4-way speaker terminal panel 1 5-way terminal block 1 2-way terminal block 1 panel mount 3AG fuseholder 1 10A 3AG fuse 2 knobs to suit VR5 and VR6 5 16-pin IC sockets 5 14-pin IC sockets 2 3mm x 6mm bolt 3 3mm x 15mm bolt 5 3mm star/crinkle washer 5 3mm nut 2 6PK x 5mm screw 19 PC stakes Semiconductors 3 LM324 quad op amps (IC1IC3) 1 4093 quad NAND gate (IC4) 1 4019 4PDT switch (IC5) 1 4029 up/down counter (IC6) 1 4051 1-of-8 multiplexer (IC7) 1 4081 quad AND gate (IC8) for each frequency with the ramp reference signal from IC4d which is connected to the inverting input of each comparator. Pulse generator IC4d is one section of a 4093 quad 24  Silicon Chip 4 BUK456/A/B/H Mosfets (Q1Q4) 1 7805 5V regulator (REG1) 1 39V 5W zener diode (for AC operation) 18 1N914 small signal diodes (D1-D18) 1 1N4004 power diode (D19) 5 5mm red LEDs 1 400V 35A bridge rectifier BR1 (for AC operation) 4 50kΩ trimpots, horizontal PC mounting (VR1-VR4) 1 100kΩ log PC-mount potentiometer (VR5) 1 1MΩ linear PC-mount potentiometer (VR6) Capacitors 1 2200µF 25VW PC electrolytic 3 100µF 16VW PC electrolytic 7 10µF 16VW PC electrolytic 1 2.2µF 16VW PC electrolytic 4 1µF 16VW PC electrolytic 1 0.12µF MKT polyester 2 0.1µF MKT polyester 1 .068µF MKT polyester 1 .056µF MKT polyester 3 .047µF MKT polyester 3 .033µF MKT polyester 1 .022µF MKT polyester 2 .015µF MKT polyester 1 .0068µF MKT polyester 3 .0022µF MKT polyester Resistors (0.25W, 1%) 2 1MΩ 1 18kΩ 1 510kΩ 4 11kΩ 3 470kΩ 18 10kΩ 4 220kΩ 2 5.6kΩ 3 180kΩ 2 4.7kΩ 3 100kΩ 2 3.3kΩ 1 47kΩ 1 2.2kΩ 1 39kΩ 1 1.8kΩ 1 27kΩ 6 1kΩ 8 22kΩ 1 470Ω 1 68Ω 1W (AC operation) Miscellaneous Tinned copper wire, hookup wire NAND gate which is con­ nected to function as a pulse generator with a positive duration of about 1ms and a period of 20ms; ie, the pulse repetition rate or frequency is 50Hz. Each time the output of IC4d goes high, diode D18 charges the 0.1µF capacitor to +10V and this capacitor will discharge exponentially through the 10kΩ and 39kΩ resistors. This gives us the falling ramp waveform shown in Fig.3. As noted above, whenever the slowly varying input DC signal to a comparator is above the level of the 50Hz reference signal, the output of that comparator goes high to turn on the associated Mosfet. However, the comparator outputs do not change state (ie, go low or high) fast enough to drive the Mosfet gates directly. Instead, the four comparator outputs go via IC5 and then via the 4081 quad AND gate IC8. This is used as a buffer to speed up the rising and falling edges of the comparator outputs. Hence, comparator IC3a connects via IC5 to AND gate IC8d which drives Mosfet Q4. Each Mosfet gate is connected to the 0V line via a 10kΩ resistor. This ensures that the Mosfets are held off when the power to the driving circuitry is off. This is important because the 12V supply to the lamps and Mosfet drains is always connected and the power switch only switches the power to the 3-terminal regulator. Well that’s how the DISCO section works. Now let’s look at the other functions. In the DISCO mode the moving contact of switch S4b is con­nected to +10V. This holds pin 14 of IC5 and pins 8 & 9 of IC4c high. IC4c acts as an inverter and so pin 9 of IC5 will be low. Under these conditions, IC5 feeds the four comparator outputs through to the Mosfet gates. If DISPLAY switch S4 is in the MODulated or UNMODulated position, pin 14 of IC5 and pins 8 & 9 of IC4c are held low by the 10kΩ resistor. So inverter IC4c’s output and thus pin 9 of IC5, will be high. This disconnects the Mosfet gates from the comparator outputs and connects them to the other set of inputs on pins 2, 6, 4 and 15. These inputs are fed from the 1-of-8 multiplexer 4051, IC7. This has one input (pin 3) which can be connected to any one of its eight outputs, depending on the logic levels applied to pins 9, 10 and 11. Outputs 1-4 (pins 13,14,15,12) are connected to IC5 with output 1 connected to Q1 through IC8c and so forth. Output 5 (pin 1) is connected through diodes D9-D12 so if it is high IC7 stays high, pin 10 is now low and pin 11 is toggled by pin 6 of IC6. This means that pin 1 of IC7 will toggle high and low and it will turn all the Mosfets on and off via diodes D9-D12, IC5 and so on. This means that all lamps will turn on and off at full brightness in sym­pathy with the OSCILLATOR or BEAT signal. With S3 in the CHASER position, pin 9 of IC7 is low while pins 10 & 11 are toggled by pins 6 & 11 of IC6. To modulate or not Inside the Light Show: the four Mosfets grouped at the back of the PC board drive the halogen lamps. They do not need any heat­sinks and will normally run cold to the touch. the four inputs to IC5 will be high. Output 7 (pin 2) is connected through diodes D15 and D16 to inputs 1 and 2 of IC5 and output 8 (pin 4) is connected through diodes D13 and D14 to inputs 3 and 4. Chaser control Op amp IC1c is configured as a Schmitt trigger oscillator which produces a square wave and its frequency is adjusted by VR6, the SPEED control. Op amp IC1d is connected as a comparator which is fed from trimpot VR1 through a 10kΩ resistor. This is the signal from the 200Hz filter and it goes high whenever there is a bass beat to cause the output at pin 14 of IC1d to go high. Depending on the setting of the BEAT switch S5, the output of IC1c (SPEED oscillator) or IC1d (audio beat comparator) will be used to clock IC6, a 4029 4-bit counter. We’re only using two outputs, from pin 6 and pin 11. IC6 can be made to count up or down, which we refer to as FORWARD and REVERSE in this circuit. Pin 10 and the 3-position DIRECTION switch S2 controls this function. In the FORWARD set­ting of switch S2, pin 10 is pulled high while in the centre-off position, pin 10 is pulled low by the 10kΩ resistor and so IC6 runs in the REVERSE direction. In the AUTO position of S2, we use the square wave signal from Schmitt trigger oscillator IC4b. This changes its logic level roughly once a minute and this will cause the counter to reverse the chaser direction every minute. Pattern selection IC7 and the PATTERN switch S3 control the patterns dis­played by the lamps. Assume for the moment that the DISPLAY switch S4 is set to the UNMODulated position. This will pull pin 6 of IC7 low. This is the inhibit pin and when it is high all the outputs are low. By pulling pin 6 low, we enable the outputs, which means the output selected by the logic on pins 9, 10 and 11 will be connected to pin 3. We now vary the logic values on pins 9, 10 and 11, to obtain the three patterns selectable by switch S3. For example, with S3 set to the ALTERNATE position, pins 9 and 10 of IC7 are high and pin 11 is toggled by pin 6 of IC6. This will cause pins 2 and 4 to alternately go high and low. Pin 2 will turn Q1 and Q2 on through D15 and D16, pin 4 will turn Q3 and Q4 on via D13 and D14. This will alternately turn the pairs of lamps on. Strobe & chaser With S3 set to STROBE, pin 9 of All the foregoing descriptions had the DISPLAY switch S4 in the UNMOD-ulated position whereby the inhibit pin of IC7 was held low. In the MODulate setting of S4, pin 6 of IC7 is connect­ed through a 22kΩ resistor to the output of inverter IC4a. IC4a is connected to IC3d, the low pass filter comparator and therefore responds to the bass beat of the music. Now what happens is that the lamps respond in the pattern set by the display switch; ie, chaser, strobe or alternate but instead of flashing to full brightness, their brightness varies in sympathy with the loudness of the bass beat. Power supply As shown on the circuit, the input from a 12V DC power supply or battery is fed via a 10A fuse, direct to the lamps and to the power switch S6. So, as already noted, there will be voltage present at the drains of the Mosfets while ever 12V is present at the supply inputs. That is why it is important for the gates of the Mosfets to be normally tied low. Following switch S6, the supply is fed via diode D19 to a 3-terminal 5V regulator which is connected to provide +10V and +5V supply rails. The +5V rail is used as a convenient “half supply” reference to bias the op amps in the circuit; ie, IC1a, IC1b and IC2a, b, c & d. The other op amps are wired as oscilla­tors or comparators so they don’t need the same biasing. Both the +10V and +5V rails are bypass­ed with 10µF and 100µF capac­ itors respectively, to provide decoupl­ ing and bypassing of high frequency “hash”. That completes the circuit description. Next month we’ll present the constructional information for 12V AC and DC versions of the circuit plus SC a troubleshooting proce­dure. January 1998  25