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By John Clarke ELECTRONIC Wind Chimes Aaaah . . . wind chimes! They’re so soothing . . . listening to the random notes as the wind creates its own melodies. But what do you do if there’s no wind? Aim a fan at it? We have a better idea: our Electronic Wind Chimes removes your reliance on the wind, and even gives you the possibility of playing tunes using the wind chime, enriching the experience! T his circuit drives a wind chime it. Read on to understand why this at their tuned frequency when struck. The clapper is moved by a sail, which using solenoids. It does so in a is so. is driven by the wind. Fig.1 shows the way that neither affects the tobasic arrangement. nality of the result, nor prevents the Wind chime basics Wind chimes play a series of notes The notes and sounds are very dechimes from being operated by the wind in the normal way. So you get that are generated by a clapper strik- pendent on chime tube length, thicking the sides of chime tubes. These ness and diameter and the hanging the best of both worlds. More good news is that electroni- tubes hang freely, so they can resonate point. The frequency is cally, it is fairly simhigher with smaller ple and uses readily- Features & Specifications wind chimes – these available parts. So you • Drives wind chimes with up to 12 elements (or multiple smaller chimes) tinkle away with a should not have diffi- • Suits a wide range of sizes from miniature chimes up to large ones light breeze, producculty building it, nor • Individual calibration of solenoid drive control parameters ing high-pitched notes is it likely to break the • Sequence recording and playback at a fast rate. Larger bank. • Sequences with long delays can be recorded in shorter periods wind chimes produce However, you will • Optional randomisation of the time between chime strikes lower-frequency tones need a degree of me- • Adjustable randomisation parameters at a slower rate. chanical skill to make • Optional automatic switch-off in darkness siliconchip.com.au Australia’s electronics magazine February 2021  61 where it produces an entirely different tone to the resonance sound of the chime tube. Often, the clapper is a circular piece of timber with a bevelled edge, so that a small area of its side strikes the tube. Timber clappers are much better than metal types. Once struck by the clapper, a chime tube will move away from its resting position due to kinetic energy transfer. The chime tube will resonate to produce sustained tones that differ from the initial strike sound. If you are after more detail on wind chimes, the science behind them and how to build them, a good site to visit is www.leehite.org/Chimes.htm This includes calculators to design a wind chime to produce the desired notes. Be aware that the notes perceived from a wind chime can be very different from the fundamental resonance of each chime tube. duced in this manner is rather poor. A very simple solenoid-driven wind chime arrangement is shown in Fig.2. The solenoid push ends can be arranged to strike the chimes in a straightline wind chime, which can be made from a disassembled wind chime. While this is easy to build, apart from poor sound, it also has the disadvantage that it can no longer be played by the wind. A more complex solenoid-driven wind chime, which retains the original configuration, is shown in Fig.3. Good sound quality is maintained by using the solenoids to pull the clapper that, in turn, strikes the tubes similarly to when driven by the wind. Additionally, the wind chime is not significantly prevented from its normal operation of playing sounds due to wind. So building this device involves some electronic assembly, mechani- Solenoid drive The biggest challenge in making solenoid-driven wind chime is in maintaining the original sound quality. While a wind chime could be played using solenoids that directly strike the chime tubes, the sound pro- Wind chime sound quality is also dependent upon the clapper. Its mass, density, shape and what it is made from very much determines what sound you get. Tonal differences can be demonstrated by tapping the chime tube with various implements such as a screwdriver blade, screwdriver handle and various pieces of timber. Compare the resulting sounds against the original clapper. When using a good-quality wind chime, the clapper will enhance the sound. A low-quality wind chime will have the sound spoiled by the clapper, 62 Silicon Chip Fig.1: in a standard wind chime, the wind blows the sail which moves the clapper, bringing it into contact with the chime tubes. Each time it strikes a tube, it makes a sound and then bounces off, possibly hitting other tubes. The result is a non-repetitive series of tones, varying with the strength and direction of the wind. Australia’s electronics magazine Fig.2: the easiest way to drive a wind chime with solenoids would be to rearrange the tubes in a row and then place a row of solenoids alongside. This is not a very good approach, though, as the solenoid plungers will make a different sound when striking the tubes compared to the (usually timber) clapper. Also, this modified chime would no longer work the same (or possibly at all) when driven by the wind. siliconchip.com.au cal fabrication and a little bit of woodworking. The electronic side involves the assembly of a circuit board, initial solenoid calibration and other adjustments. On the mechanical side, you need to arrange the solenoids and other bits and pieces to activate the clapper. The woodworking aspect involves making a frame to support these solenoid movements, which are arranged around the outside of the wind chime. Design features Our Electronic Wind Chime circuitry can drive up to 12 solenoids, so it can be used to play up to 12 different chimes. These chimes don’t have to be within the same wind chime. You could use the same circuitry to control two or more wind chimes, so long as there are no more than 12 chimes in total. You can also mix and match solenoids – for example, using smaller solenoids for small chimes and larger solenoids for larger chimes. Each solenoid can be independently set up for how it is driven. There are two adjustments. One controls the voltage applied to each solenoid. This can be varied from the full 12V down to near 0V via pulse width modulation. This feature is used to prevent the solenoid from being too aggressive. A lower voltage will slow down the solenoid action, so that the wind chime is not sent into disarray. The second adjustment is the duration the solenoid is driven. This needs to be sufficient to allow it to produce a strike against the chime and then pull away before the chime tube returns. The electronics includes the option to manually ‘play’ the wind chime by pressing small pushbutton switches. These are useful during calibration, to check whether each chime is being struck correctly. But these switches have another purpose – you can record a sequence by manually playing the solenoids using these buttons, then play it back later, to play a tune (for example). The sequence of solenoids and the period between each activation is recorded. There is also a facility to record long breaks between solenoid strikes without having to wait the full period. This feature increases the period that’s recorded by a factor of 10, so you can record a very long, slow sequence in a reasonable amount of time. During recording, a variety of different sequences can be included. This siliconchip.com.au Fig.3: while more work to achieve, this arrangement is far superior as it allows the chime to be driven by the wind or electronically, depending on the weather and your mood. It also retains the original tone. The solenoids now press on levers that pull the clapper via a string to strike the associated tube. A second set of strings prevents the chimes from swinging back and striking the clapper again, due to inertia, unless the associated solenoid is re-energised. Australia’s electronics magazine February 2021  63 l l Fig.4: the circuit for the Electronic Wind Chime comprises mainly microcontroller IC1 and transistors Q1-Q24, which are used to drive the solenoids. For each pair of transistors (Q1 & Q2, Q3 & Q4 etc), only one is fitted. The BC337s work up to 500mA while the Mosfets can handle up to 3A. The rest of the circuit allows you to set up the unit, record a sequence and optionally, have it switch off at night. l SC Ó ELECTRONIC WINDCHIME will decrease the perceived repetition as the played back sequence repeats in a loop. The recording time available is well over what you might require. This means that you are free to record without concern of running out of memory. The recording is permanently stored, unless overwritten with a new recording. There is also an option to randomise the pauses between solenoid strikes 64 Silicon Chip during playback. At the maximum randomness setting, the delays vary between one and five times longer than those recorded. The randomness changes to a new value at intervals of between 10 seconds and 21.25 minutes; this, in itself, varies randomly. This is all designed to remove any hint of a machine-driven wind chime, making it sound more natural. The maximum randomness values Australia’s electronics magazine can be changed to smaller values if desired. Optionally, the Electronic Wind Chime can be set to switch off during darkness. This is useful if you (or your neighbors!) prefer peaceful serenity at night. Circuit details The circuitry, shown in Fig.4, is based around microcontroller IC1. It stores the recorded sequences in its siliconchip.com.au Scope1: the 500Hz, 5V PWM drive to the base/gate of the output transistor is shown in the top trace (yellow) with a 50% duty cycle, and the resulting (inverted) 12V drive voltage to the solenoid is shown below in cyan. The duty cycle (ie, percentage of time that the solenoid receives current) is adjustable for each solenoid, to control how hard it is driven. flash memory, then plays them back by using its digital outputs to drive transistors or Mosfets that, in turn, drive the solenoids. The microcontroller also monitors a light-dependent resistor (LDR1), a control switch, jumper link and a trimpot and drives a status LED (LED1). Twelve of IC1’s twenty pins are used as digital outputs for driving the solenoids. There are two types of solenoid drivers you can use. One option is NPN transistors for driving low-current solenoids. This is a considerable cost saving compared to N-channel Mosfets, but Mosfet drivers must be used for solenoids that draw over 500mA. There is a small circuit change when using a transistor rather than a Mosfet: the resistor value (R1-R12). When a transistor is used, the resistor value is 2.2kΩ, which sets the transistor base current. For a Mosfet, the resistor value is 100Ω instead, and this drives the Mosfet gate. Diodes D1-D12 at the transistor collector or Mosfet drain are there to conduct the reverse voltage (backEMF) from the solenoid coil when it is switched off. This protects the bipolar transistor or Mosfet from damage. PWM drive The solenoids can be driven with a PWM signal. This is where the Mosfet or transistor is switched on and off at 500Hz with a particular duty cycle. The average voltage produced is the duty cycle multiplied by the supply voltage. So for a 12V supply and a 50% duty cycle, the average voltage applied to the solenoid is 6V. The frequency needs to be high siliconchip.com.au causes the associated solenoid to be driven with the full 12V for the duration that the switch is pressed. But when the solenoid is driven via the microcontroller, the drive is a PWM waveform with a preset on-period and duty cycle. More circuit details enough to prevent the solenoid from driving the plunger in and out at the PWM rate. But too high a frequency can also cause problems such as increased dissipation in the transistor/Mosfet or reduced response from the magnetic properties of the steel core. Our choice of 500Hz was suitable for a wide variety of solenoids that we tested. Oscilloscope waveform Scope1 shows the gate drive to the Mosfet at the top (yellow) with a 5V drive voltage. The drain voltage waveform (blue) is the lower trace with a 12V supply voltage. The solenoid has 12V across it when the drain voltage is 0V, and 0V across it when the drain is at 12V (the negative end of the solenoid connects to the drain). The duty cycle is around 50% at almost 500Hz. The solenoid driver pins on IC1 usually are set as inputs. The Mosfet or transistor is held off via the associated 10kΩ pull-down resistor. Having the pins as inputs allows switches S1-S12 to pull the input high when pressed. If the pin were set as a low output instead, the pull-up switch would ‘fight’ the microcontroller output, causing a high current through the output pin. The pin is changed to a high-level output when required to switch on the Mosfet or bipolar transistor. In this case, pressing the associated switch will not cause problems since the output is already high. For a low level, the pin is made an input again, so the Mosfet or bipolar transistor switches off (unless the associated switch is currently being pressed). Note that pressing switches S1-S12 Australia’s electronics magazine IC1’s pin 18 (digital input RA1) monitors the LDR so that the circuit can optionally switch off at night. During the daytime, the LDR resistance is low, so pin 18’s voltage is below the low threshold of the RA1 input. A 100kΩ resistor and trimpot VR2 form a voltage divider with the LDR across the 5V supply. This trimpot allows the detected light threshold to be varied. When the LDR is in darkness, the LDR resistance is high, and this pull-up resistance causes the RA1 voltage to be above its high threshold. IC1 detects this, and the software stops running. The RA3 digital input monitors control switch S13. This pin can be used as an external master clear signal (MCLR) or a general-purpose input. We are using it as an input, and it is usually pulled high, to 5V, by the 10kΩ resistor. This input goes low when the switch is pressed; it serves many functions, as described later. The status LED (LED1) is driven via the RC1 output via a 1kΩ resistor. It is used to indicate various modes when recording a sequence and calibrating the solenoid settings. Trimpot VR1 is connected across the 5V supply, and its 0-5V wiper voltage is monitored at IC1’s analog input AN4 (pin 16). VR1 sets the solenoid pulse width/duty cycle and drive duration in conjunction with jumper JP1. JP1 is monitored by IC1’s RA0 digital input (pin 19). This input is held high by the 10kΩ pull-up resistor unless there is a shorting link across JP1, which would pull it low. Power supply 12V power for the circuit is applied at CON7. This flows to the solenoids is via fuse F1. This supply is bypassed with two in parallel 1000µF low-ESR capacitors, which help to supply the peak solenoid current. Reverse polarity protection uses 3A diode D14. If the supply is connected backwards, this conducts to blow the fuse. February 2021  65 Fig.5: circuit board assembly is straightforward; simply install the components as shown here. Small rectangles are provided above the manual control switches so you can write the musical note produced by that switch, or a solenoid number. During construction, take care with the orientations of the diodes, ICs, transistors, terminal blocks and electrolytic capacitors. SILICON CHIP The voltage to the remainder of the circuit is applied via reverse polarity protection diode D13, and is switched by S14 before being applied to the input of the 5V regulator, REG1. Two 100µF capacitors, one at the regulator input and the other at the output improve the regulator’s stability and transient response. Microcontroller IC1 also has two 100nF supply bypass capacitors pins at pins 1 and 20. LED2 lights up when power is applied, with its current limited to around 2-3mA by its 1kΩ series resistor. Memory storage Twelve bytes of the flash memory are dedicated to storing the PWM duty cycle and on-period parameters for each solenoid (ie, one byte per solenoid). 1182 bytes of flash memory are used for storing the playback sequence. Two bytes of memory are used to record which solenoid(s) to activate, followed by a two-byte delay period. Each delay period can be up to 10.9 minutes in 10ms steps. If the delay period is over 10.9 minutes, then the next two bytes continue that delay. 66 Silicon Chip This means that the maximum sequence can be up to 107 hours (1182 ÷ 2 x 10.9 minutes). However, as extra bytes are consumed for each solenoid strike, the practical maximum is somewhat less than that. For a more realistic calculation, say that a recording consists of a series of eight strikes, spaced two seconds apart, with a 10-second delay before the next little tune. That consumes 32 bytes (8 x 4 bytes) for every 24 seconds of recording (7 x 2 seconds + 10 seconds). The 1182 byte memory can record up to 37 such sequences, for a total recording or playAustralia’s electronics magazine back time of 888 seconds or 14.8 minutes. Typically, you would leave a longer period between solenoid drive sequences, so the maximum recording (and hence playback) time will be longer. There is no need to completely fill the memory, as during playback, it only cycles through the number of bytes that were recorded in memory PCB assembly The Electronic Wind Chime circuit is built on a PCB coded 23011201 which measures 147 x 87.5mm – see Fig.5. This fits into a UB1 Jiffy box. Which siliconchip.com.au parts you install depends to some extent on the number of solenoids you will use and the solenoid sizes. See the accompanying panel on this topic. The parts list specifies the parts required to drive the maximum 12 solenoids. Asterisks indicate which parts you can buy fewer of if you plan to drive a smaller number of solenoids. This includes S1-S12, R1-R12, the 10kΩ pulldown resistors, Q1-Q24, D1-D12 and CON1-CON6. CON1 and CON6 are three-way terminal blocks, with two terminals for a pair of solenoids plus a common positive connection for each set of six. CON2-CON5 are two-way terminal blocks which do not have the common positive connection, only the negative connections for two solenoids. So if you have an odd number of solenoids, you will end up with an unused terminal in one of the connectors. You can have a mix of low- and highcurrent solenoid drivers. Say you might wish to control two wind chimes, with each having three large chimes and three smaller ones. You could fit Mosfets at the evennumbered positions (Q4, Q8, Q12 etc) and corresponding 100Ω gate resistors. You would then fit transistors at the odd-numbered Q position (Q1, Q5, Q9 etc) with 2.2kΩ base resistors, for the smaller chimes. Do not install both a Mosfet and bipolar transistor in the same position. This complicates construction a little, but you can save quite a bit of money as the bipolar transistors cost far less than the Mosfets. Start by fitting the resistors on the PCB where shown (remember to vary the R1-R12 as described above). The resistor colour codes are shown in the parts list, but it’s always best to check the values with a digital multimeter (DMM) set to measure resistance. Continuing on, install diodes D1 to D12 (or as many as required) and D13. Make sure that the cathode stripes face toward the top of the PCB as shown. Also fit D14 now, which faces the opposite direction compared to the others, and is the largest diode. Then mount switches S1-S12 (where used) and S13. These will only fit onto the PCB the right way, so if the switch does not seem to fit, try rotating it by 90°. We recommend that IC1 is installed using a socket. Make sure the end notch faces toward the left edge of the PCB. siliconchip.com.au Parts List – Electronic Wind Chimes 1 double-sided plated-through PCB coded 23011201, 147 x 87.5mm 1 UB1 Jiffy box, 158 x 95 x 53mm [Jaycar HB6011 (black), Altronics H0201 (black) or H0151 (grey)] 1 12V DC plugpack or similar supply, ideally with 2.5mm ID barrel plug (current rating dependent on solenoids used, up to 3A maximum) 12* 12V DC spring-return pull solenoids with lever slot [see text] 2* 3-way screw terminals with 5.08mm spacing (CON1,CON6) 4* 2-way screw terminals with 5.08mm spacing (CON2-CON5) 12* SPST momentary switches (S1-S12) [Altronics S1120, Jaycar SP0600] 1 SPST momentary switch (S13) [Altronics S1120, Jaycar SP0600] 1 SPDT toggle switch (S14) [Jaycar ST0335, Altronics S1310] 2 M205 PCB-mount fuse clips (F1) 1 3A M205 fast blow fuse (F1) 1 5A DC PCB-mount 2.5mm ID barrel socket (CON7)   [Jaycar PS0520, Altronics P0621A] 1 20-pin DIL IC socket (for IC1) 1 48kW to 140kW light-dependent resistor (LDR1)   [Jaycar RD3480, Altronics Z1619] 2 2-way pin headers with jumper shunts (JP1,JP2) 2 PC stakes (optional; GND & TP1) 2 or more cable glands for 3-6.5mm cable entry Semiconductors 1 PIC16F1459-I/P 8-bit microcontroller programmed with 2301120A.hex (IC1) 1 7805 1A 5V regulator (REG1) 1 3mm red LED (LED1) 1 3mm green LED (LED2) 12* 1N4004 1A diodes (D1-D12) 1 1N4004 1A diode (D13) 1 1N5404 3A diode (D14) Capacitors 2 1000µF 16V PC low-ESR electrolytic 2 100µF 16V electrolytic 4 100nF MKT polyester Resistors (all 1/4W 1% metal film 1 100kW (Code brown black black orange brown) 12* 10kW (S1-S12 pull-down resistors) (Code brown black black red brown) 2 10kW (Code brown black black red brown) 2 1kW (Code brown black black brown brown) 1 500kW miniature horizontal trim pot, Bourns 3386P style (VR2) (Code 504) 1 10kW miniature horizontal trim pot, Bourns 3386P style (VR1) (Code 103) Parts for high-current solenoid drivers (>500mA) 12* STP16NF06L, STP60NF06L or CSD18534KCS 60V, 16/60/73A logic-level N-channel Mosfets (Q2,Q4,Q6...Q24) [Jaycar ZT2277 or SILICON CHIP ONLINE SHOP Cat SC4177] 12* 100W 1/4W 1% metal film resistors (R1-R12) (Code brown black black black brown) Parts for low-current solenoid drivers (<500mA) 12* BC337 NPN 500mA transistors (Q1,Q3,Q5...Q23) 12* 2.2kW 1/4W 1% metal film resistors (R1-R12) (Code red red black brown brown) Miscellaneous Suitable exterior board or timber, aluminium sheet, wire loom, cable ties, wire, screws, paint, string etc * reduce these quantities for driving fewer than 12 solenoids and note that low- and high-current solenoid drivers can be mixed and matched (up to a total of 12) Australia’s electronics magazine February 2021  67 The trimpots can be installed next. VR1 is the 10kΩ trimpot that may be marked as 103 rather than 10k. VR2 is 500kΩ and may be marked as 504 rather than 500k. Now mount the fuse clips, making make sure these are installed with the correct orientation, ie, with the end stops toward the outside of the fuse. It is a good idea to insert the fuse before soldering the clips to ensure the fuse is aligned within the clips, and that the clips are orientated correctly. PC stakes can also be installed at GND and TP1. However, these can be left out, and multimeter probes pressed directly onto the pads for voltage measurements. Fit the two-way headers for JP1 and JP2 next, then the DC socket (CON7). Follow with the 3-way and 2-way screw terminals (as many as needed), with the wire entry holes towards the lower edge of the PCB. Now mount the capacitors, noting that the electrolytic capacitors must be orientated correctly, with the longer positive leads through the holes marked “+”. Transistors It is time to fit the transistors and/or Mosfets (along with regulator REG1), noting again that which ones and how many you install depends on what solenoids you are using, and how many. The power switch (S14) and the two LEDs can be mounted in one of two ways: either directly on the PCB or onto the lid of the box, with wires making the connections between the component and PCB. We opted to mount the switch and LEDs on the PCB – this way, they will not be seen or accessible once the lid of the box is in place, but that’s OK as they are mainly used during setup and recording. Without the power switch being accessible, the unit can still be switched on and off via the 12V plugpack. If you intend to use the LDR to switch the unit off at night, solder this in place now. It can be mounted so that the face of the LDR is toward the back edge of the PCB (by bending the leads), so it is exposed to the outside light via a hole in the side of the enclosure. If you don’t need the LDR feature, link it out or place a shorting block over jumper JP2. Housing The PCB is held in the plastic case by the integral clips holding the sides of the PCB. You will need to drill holes in the box for the DC socket and the solenoid wiring. We recommend that this wiring passes through several cable glands before being connected to CON1-CON6. The 9mm hole for the DC socket is 21mm above the outside base of the case and 26mm in from the outer edge. Cable glands can be placed 15mm down from the top edge of the enclosure, adjacent to the screw connectors CON1-CON6. Next month The electronics section is now virtually complete, but we still need to describe how to modify your wind chime to add the solenoids, plus the testing, setup and sequences recording procedures. All that will all be covered in a second article next month. This PCB has five high power Mosfets in positions Q2-Q10 with seven lowerpower transistors in Q11-Q23. The reason (and difference) is explained in the text. The PCB mounts in the case without screws – it simply clips into the slots on the side guides. As yet, the holes are not drilled into the lid for the on/off switch nor LED – these can be done using the front panel artwork as a template. We’ll look at this in more detail next month. 68 Silicon Chip Australia’s electronics magazine Choosing your solenoids The circuit has been designed to cater for many types of solenoids. We used D-frame spring-return pull types, although push-pull types can also be used. The sizes available range from miniature through to heavy-duty types that can draw up to 3A. What you need depends on the size of the wind chime you are using. There are several specifications you need to look for; for example, the circuit requires 12V solenoids. Another important specification is the movement length, or stroke. Other useful features are a means to attach to the solenoid plunger. Some will have holes in the plunger, but others will not have any means to attach anything to the solenoid plunger. For small wind chimes, a solenoid stroke of 4mm might be sufficient, but for larger chimes, something like 12mm is required. For use with mini wind chimes (tubes around 6.35mm in diameter) and using a direct solenoid plunger hit to an inline set of chimes as shown in Fig.2, a push-pull solenoid with a frame section that measures 21 x 11 x 10mm having a 4mm stroke would be suitable. Their overall length is 30mm, and they draw 120mA at 12V DC. The solenoids for the wind chime we used have a 30 x 16 x 14mm frame section and 10mm stroke. Their overall length is 55mm. The plunger includes a mounting slot and securing hole suitable for a lever attachment. At 12V DC, they draw 2A. The initial pull is 300g with an ultimate retention force of 3kg when fully closed. Both Jaycar and Altronics sell suitable solenoids, and many others are available via on-line marketplaces such as eBay. SC siliconchip.com.au