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ELECTRONIC Wind Chimes Part 2: finishing it off – by John Clarke Last month, we described how our new Electronic Wind Chime worked, and how to build the electronics. Now we get to the tricky bit – modifying the wind chime itself so it can be driven by a series of solenoids. Fear not, because we have detailed instructions on how to accomplish this, and finish the build by putting it all together and setting up the electronics. W Our finished Electronic Wind Chime. It’s based on a commercial wind chime but ours works when there’s no wind. 92 Silicon Chip e modified a Carson Home Accents “Amazing Grace” 640mm Sonnet Wind Chime to incorporate the solenoid drivers. It is a 5-chime type with 31.5mm outside diameter tubes. The longest tube is 590mm and shortest at 450mm. The solenoids are supported on a circular ring made from 9mm MDF (medium-density fibreboard). This ring is held in place with an inverted U-shaped piece made from MDF and a couple of right-angle brackets. The whole frame is attached to the wind chime’s attachment hook with an M5 screw and nut. For our prototype, the clapper plate was made using an 80mm diameter piece of 1mm aluminium sheet. The plate (shown in Fig.7) is designed to cater for the 5-chimes arranged 72° apart around the diameter. The plate includes holes for the strings and a slot to allow the clapper plate to be placed over the clapper while its central support string is still attached. The frame needs to be sized so the base plate can be positioned at a height where the solenoids and levers are inAustralia’s electronics magazine line with the top of the clapper plate. There are two holes for the string attaching each solenoid to its chime. These need to be far enough apart so that the string does not touch the chime tube when pulled taut. This clapper plate can be glued in place, or held with a small self-tapping screw into the clapper after the string has been threaded. The 100mm x 10mm rectangular solenoid levers are made from 1mm aluminium sheet; the two end holes are 3mm in diameter. Note that two holes are not centred, but placed close to one side, to give the best rotational movement when attached to the solenoid plunger. The pivot point is a wood screw into the base plate. This should be long enough and screwed in sufficiently for the lever to sit horizontally, without being too tight to move. The hole in the solenoid plunger was drilled to 2.5mm and then tapped for an M3 thread. That allows the lever to be secured at the fulcrum with just a 10mm-long M3 screw and no nut, with the screw acting as a bearing. Alternatively, you could drill 3mm diameter holes and secure them with machine screws and nuts. siliconchip.com.au A close-up of the “business” end of the electronic wind chimes, showing how the solenoids are placed around the ring. The solenoids do not strike the chime tubes; rather, they pull the clapper towards the tube which makes the sound. In this photo, some of the catch strings and pull strings were removed from the closest chime tubes for clarity. The pivot hole is slightly elongated by about 1mm, to allow for the lever to move freely, allowing for length changes between the screws as it rotates with solenoid movement. A 6.3mm-long untapped spacer keeps the pivot raised and is secured with a 15mm-long No.9 countersunk wood screw into the base plate. The solenoids are attached using screws into the solenoid housing. Our solenoids have M2.5-tapped mounting holes, so they are secured using M2.5 x 12mm screws. If no holes are provided, they can be glued in place instead. Other options The clapper plate and levers could be made from a material other than aluminium. The levers need to be thin siliconchip.com.au enough to freely rotate within the solenoid plunger slot. An easier material to work with is the Presspahn or similar electrical insulation material, such as the Jaycar HG9985. This can be cut with scissors and a sharp craft knife. The sizes given for the wooden frame and base plate are notional; these really depend on the wind chime you are using. The circular ring base plate needs to have an inside hole large enough so the chime tubes can freely swing without hitting it. The outer diameter needs to be sufficient for attaching the solenoids, with room for the pivot screws. While we used MDF for the frame and base plate, you could make the Australia’s electronics magazine frame from solid timber instead. The base plate does not need to be circular – it could be made in a polygonal shape instead. The number of straight sides could equal the number of chimes; for our 5-tube chime, that would be a pentagon. Note that once the solenoids and levers are in place, there is not necessarily a convenient point to attach the frame to the chime where it will not interfere with at least one lever. This is especially true with an odd number of solenoids. However, there should be one side of the frame that can be directly attached to the base plate. The other leg can be supported with a bracket that is raised above the base plate using a screw and March 2021  93 nuts to clear lever movement (see our photos for details). Alignment Reproduced from last month, this shows our recommended arrangement for the solenoids to drive the wind chimes. The solenoids press on levers that pull the clapper via a string to strike the associated tube. A second set of strings prevents the clapper from swinging around and hitting other tubes unless the associated solenoid is energised. 94 Silicon Chip Australia’s electronics magazine The frame needs to be aligned correctly to the base plate. This is so that when the frame is held by the wind chime attachment hook, the solenoid levers and strings are positioned correctly, so that the clapper is pulled along the radial line from the centre of the clapper to the centre of the chime tube for each solenoid. If it is not possible to get this alignment without the frame interfering with the solenoid drivers, the positioner at the top of the wind chime may need to be rotated. Rotating the chime positioner will effectively twist up the strings at the attachment hook, so it will not stay in this rotated position. The solution is to tie the chime positioner against the side of the frame. A small hole in the side of the chime positioner and another in the frame will allow for a short length of string or stiff wire to hold the chime positioner in its rotated position. Stringing the chime The pull strings must normally be loose. These pull the clapper toward the chime near the end of the lever travel. The loose stringing is for two reasons: firstly, the solenoid pulling force is not particularly strong at the beginning of its movement from its resting position, and it is greatest when it fully pulls in the plunger. The looseness allows the solenoid to ‘build up strength’ before it starts moving the clapper. The second reason is so that when one solenoid pulls the clapper in its direction, it is not affected by the strings becoming taut on the opposite side. The looseness needs to be a compromise between being tight enough to be able to pull the clapper against the chime, and loose enough not to affect the opposing solenoid pulls. The strings pass through the clapper holes and back to the lever, and are secured by passing the string through the lever hole. An M3 x 6mm screw and M3 nut can be used to secure the string in the hole. This more easily allows fine adjustments compared to tying a knot. A refinement to the design is to include catch strings. These catch and siliconchip.com.au hold the chime tube, preventing it from swinging back to re-strike the clapper after striking the chime tube. Their lengths are such that they are loose when the tube sits in its usual position, but is tight enough to prevent it swinging back and hitting the clapper. The string ends are held to the base plate by clamps. We used polyester string, which becomes unravelled if cut with scissors or a knife. Instead, the string was cut to lengths with a hot soldering iron tip that both cut and welded the string ends to prevent fraying. We don’t recommend you use your primary, highquality iron to do this, though! You can also cut the string and then use a lighter to weld the ends before they unravel. Wiring Use sufficient gauge wire (eg. 19 x 0.1mm strands) or similar for the larger solenoids, so that voltage drops will not affect solenoid operation. If the wire cross-sectional area is too small, then the solenoids may not work with longer wire runs back to the main PCB. We used a 7mm tube loom to hold the wires in place and keep the appearance neat. The +12V wires to each solenoid are connected together and brought back to terminate into the positive terminal of CON1 or CON6. The second wire of each solenoid connects between the solenoid outputs at CON1-CON6 and the negative terminal of the solenoid. After soldering the solenoid wires to the extension wires, insulate the joints using electrical tape or heatshrink tubing. When finished, we attached the wire loom to the top of each solenoid using cable ties so that it won’t move around. The main enclosure housing the PCB can be located on a timber beam above the wind chime attachment, or further away out of sight. S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 Randomness off Randomness on Delay varies in 128 steps between 10s and 1280s (21:20) Delay varies in 64 steps between 10s and 640s (10:40) Delay varies in 32 steps between 10s and 320s (5:20) Delay varies in 16 steps between 10s and 160s (2:40) Delay varies in eight steps between 10s and 80s (1:20) Delay varies in four steps between 10s and 40s (0:40) Delay multiplier varies randomly between one and five times actual Delay multiplier varies randomly between one and three times actual Delay multiplier varies randomly between one and two times actual Delay multiplier varies randomly between one and 1.5 times actual Table 1 – switch actions at power-up remove the shorting block from JP2 and switch on the power. LED2 should light, indicating that there is power. VR2 can then be adjusted to set the light threshold that switches the Electronic Wind Chime on or off. With the LDR in normal shaded daylight, place your finger over the LDR and adjust VR2 so that LED1 (the status LED) starts flashing at 2Hz. This indicates that playback is paused. Lifting your finger from the LDR should result in that LED switching off. The more clockwise VR2 is adjusted, the darker the light needs to be to pause playback. Calibration The LDR is ignored during calibration and recording. It is only used during playback, and only if JP2 is open. This is so that calibration and recording are not interrupted by a change in light level. Each solenoid can be independently calibrated for the drive voltage (using PWM) and for the on-period. These two parameters are adjusted using VR1 and JP1, as described below. The 500Hz PWM duty cycle can be adjusted between about 5% to 100% in approximately 0.75% steps. This varies the average voltage between Fig.6: we cut a sheet of aluminium to this shape and screwed it to the top of our timber clapper, to allow the five strings to be easily attached. Setting up There are several options that need to be set in the Electronic Wind Chime controller before you can use it. LDR adjustments If you prefer not to have the Wind Chime paused during darkness, place a shunt on JP2. In this case, the LDR does not need to be installed. But if you do want it to stop at night, siliconchip.com.au Australia’s electronics magazine March 2021  95 600mV and 12V in about 90mV steps. The on-period can be set to between 2ms and 254ms in approximately 2ms steps. Initially, all solenoids receive the full 12V drive voltage (100% duty cycle) for a duration of 254ms. To initiate calibration, press and hold the control switch (S13) at power-up. The status LED (LED1) lights for 200ms then flashes off for 200ms and then on again. This indicates that calibration has been activated. Press a solenoid switch (S1-S12) to select which solenoid is to be calibrated. The status LED extinguishes, and the solenoid drive parameters are now ready to be adjusted for the chosen solenoid. When JP1 is shorted, the PWM duty cycle can be adjusted with VR1, and when JP1 is open, the drive duration (on-period) is adjusted with VR1. Once you have set JP1 and adjusted VR1 for the setting you want to make, press the control switch (S13) to temporarily store that particular parameter. This will also drive the relevant solenoid, so you can check whether the setting is correct. If not, readjust VR1 and press S13 again. If you want another solenoid to have the same parameter, the switch (S1S12) for that solenoid can be pressed, and the control switch (S13) pressed again to store the current parameter value for that solenoid. We have also provided a means of monitoring the current VR1 setting using a multimeter measuring the voltage between TP1 and TP GND. That makes it easier to replicate suitable values for other solenoids. The status LED (LED1) lights each time you press the control switch for the duration of the solenoid drive. Lower PWM duty cycles will cause the solenoid to move more slowly. Adjust the solenoid on-period to allow sufficient time for the solenoid to pull the clapper against the chime tube, but short enough for it to pull away before the chime tube returns after being struck. As mentioned, the solenoid parameters are initially only temporarily stored. The values will be lost when the power goes off unless they are stored in flash memory. This is also done with the control switch. While pressing the control switch for a short period tests the solenoid drive, a longer press (one second or more) will store all solenoid parameter values into the permanent flash memory. LED1 will light again if the switch is held for one second or more, to indicate that the values have been written to flash. To exit the calibration mode, switch off power. When power is switched on again, without S13 being pressed, the Wind Chime Player starts up in playback mode. You can return to the calibration mode again by repeating the above procedure, to re-adjust those parameters. Only the parameters for the selected solenoid or solenoids will be changed. Previously stored parameters will remain unchanged unless new parameters are stored for that solenoid. trol switch, S13, after power-up. The status LED, LED1, lights and stays lit, indicating that recording has begun. You can then press the individual solenoid switches to activate the solenoids, and it records the sequence you provide and the pauses in between. You can close one solenoid at a time. The PCB includes white screenprinted squares above each switch so you can write the perceived note using a fine marker pen. We say the perceived note because the sound from the chime comprises many overtones, which may affect the apparent frequency. It may also appear to shift in frequency after initially struck. The perceived note cannot be easily measured with a spectrum analyser. Probably the easiest method is to use a guitar tuner or similar device and adjust it until its apparent frequency matches the chime, then look at what note you have selected. For more information on the perception of sounds from wind chimes, see www.leehite.org/Chimes. htm#The%20strike%20note and www. sarahtulga.com/Glock.htm During recording, you can play out a tune if you are musically inclined, or just some nice sounds that appeal to you. Short gaps between chime strikes, these can be waited out in real time before driving a solenoid for another chime. Longer intervals may become tedious to wait out in real time, but we have a solution to that... Recording a sequence Time warp To make a recording, press the con- By pressing the control switch for Here’s the Electronic Wind Chime PCB placed inside the case, albeit without any cables connected, while at right the front panel and label are placed. 96 Silicon Chip Australia’s electronics magazine siliconchip.com.au longer than one second, that period stored for the current pause is multiplied by ten. The status LED flashes at 1Hz to meter out the time (one flash is one second of real time, but ten seconds of delay). Be careful when pressing S13, since if you press it for less than one second, instead of activating the time warp, it will end the recording. After a short press of the control switch, the entered sequence will be written to flash memory, and it will return to playback mode. If no solenoid switches were pressed while in record mode, the previous recording will remain in memory. Playback SILICON CHIP www.siliconchip.com.au + Power + Wind Chime ePlayer + . - . - 12VDC Input SILICON CHIP www.siliconchip.com.au Wind Chime ePlayer + 12VDC Input At power-up, the Electronic Wind Chime starts in playback mode. This plays back the recorded sequence, repeating it in a continuous loop. The initial setting is for no randomness in the delay periods between chime strikes – in other words, it faithfully reproduces your recorded sequence. Adding randomness Two front panels designs are provided – one has provision for through-panel switch and LED As mentioned earlier, whereas the other panel doesn’t. These can also be downloaded from siliconchip.com.au you can add randomness to the delay between If you haven’t already pressed any chime strikes. This is selected by press- the maximum value selected. The opat power-up, then ing switch S2 while powering up. Wait tions are 1280s (21:20), 640s (10:40), of these switches + Power for the status LED (LED1) to flash after 320s (5:20), 160s (2:40), 80s (1:20) and the initial setting is with randomness CHIP SILICON off. If randomness is switched on (us40s (0:40). about one second before releasing S2,www.siliconchip.com.au These options are selected by hold- ing S2), then the 10s to 1280s (21:20) indicating that the randomness feature ing one of switches S3, S4, S5, S6, S7 randomness change rate is selected, has been enabled. + along with the 1-5 times delay 12VDC range. The setting is stored in permanent and S8 at power-up – see Table 1. Note that you can press andInput hold You can also change how much varimemory. If you want to switch the randomness off, hold switch S1 at power ation you want in the delays. There are more than one switch at power up up and wait for the status LED to light four options, selected by holding one to select more than one option at the of switches S9, S10, S11 or S12 down one time. before releasing it. For example, you could switch ranThere are two randomness param- at power-up. The delay multiplier varies random- domness on (with S2), set the randometers that can be adjusted. One is the ly between one and the maximum value ness change rate at up to 320s with S5, rate; how often the random value changes. This can be set to six differ- selected. S9 selects a range of 1-5 times, and the randomness variation to beent values. The randomness changes S10 1-3 times, S11 1-2 times and S12 tween one and three times with S10, at an interval between ten seconds and 1-1.5 times variation (also see Table 1). all at the same time. + Wind Chime ePlayer . SC siliconchip.com.au Australia’s electronics magazine March 2021  97