Fullscreen HTML5Med Res (??MB)HTML4

Part 2 by John Clarke Background source: https://unsplash.com/photos/a-person-in-yellowgloves-and-blue-gloves-cleaning-a-floor--dc38HdQR1M Ultrasonic Cleaner adjustable Our new Ultrasonic Cleaner has adjustable frequency, transducer voltage and power. That means you can run it at low or high power, depending on what you are cleaning. The transducer can be brought into resonance for efficient power transfer even with a range of liquid levels. e explained how this new Ultrasonic the cleaning power you need, which attach to the lid. The only external wiring is for DC power to the unit and one W Cleaner works last month. Unlike our can be up to 40W. Since it runs from 12-15V DC at up twin-lead that emerges for the translast Cleaner, which automatically swept the frequency searching for the resonant point of maximum power transfer, this one lets you adjust it yourself. You can also vary the transducer voltage to vary the power level, plus it includes an automatic safety feature that reduces the power if the current draw gets too high. While it might seem odd that you need to find resonance yourself, when the previous version did it automatically, this approach has a few advantages. One is that it makes matching the transformer to the transducer less critical; that made building the previous version more difficult. Another is that it can be more tolerant of different fluid levels in the bath, as that affects the resonant frequency. With this design, you can select one of 16 different frequency bands using pushbutton switches, then adjust the frequency within those bands with a knob. Once it has been set up, the next time you go to use it, it usually won’t take long to make a few tweaks to the frequency and power knobs to achieve 30 Silicon Chip to 4A, that means you can also run it from a standard 12V lead-acid or similar battery, as long as it can provide the required current. Construction Besides the transducer, all the electronic components mount on two PCBs that are housed in a diecast aluminium box. The controls and LCD screen ducer. Both leads pass through the box via cable glands. Building the Ultrasonic Cleaner isn’t too difficult. The main steps are soldering the components to the PCBs and winding the transformer. The enclosure will require drilling and a couple of rectangular holes need to be made. PCB construction The transducer is driven with a high voltage, around 150V AC, in operation, which is more than enough to give you a shock. Touching both of the transducer terminals during operation will give you an electric shock; it will be worse if your hands are wet. You must enclose the transducer in the PVC housing described in this article and only run it when so enclosed and attached to a bath filled to the correct level with cleaning fluid. The main 159 × 111mm PCB is coded 04105261, while the smaller (98 × 60mm) front-panel PCB is coded 04105262. Both fit in a 171 × 121 × 55mm diecast aluminium case. The overlay diagrams for these boards are shown in Figs.6 & 7. Start by fitting the resistors on both PCBs where shown. The resistor colour codes were in the parts list last month, but it’s always best to check the values with a DMM set to measure resistance to make sure they’re going in the right places. The two 0.1W SMD resistors mount on the top of the PCB. Solder one end first and check alignment before soldering the other end. Australia's electronics magazine siliconchip.com.au WARNING! Fig.6: the main Cleaner PCB overlay. Leave Mosfets Q1 & Q2 for last, as need to be mounted to but insulated from the bottom of the case, with access holes for tightening their nuts. REG1, REG2 & D2 are attached to the side of the case, also for heatsinking; the two regulators require insulating washers and bushes. Continuing with just the main PCB, fit diodes D1 and D3, ensuring that their cathode stripes face toward the top edge of the PCB as shown. We recommend that IC1 and IC2 are mounted in sockets. Make sure that the notched end faces toward the lower edge of the PCB. Also mount the two M205 fuse clips now, making sure that they have the correct orientations, with the end stops toward the outside. It is a good idea to insert the fuse before soldering the clips to ensure the fuse is aligned in the clips and that the clips are orientated correctly. CON1, CON2 and CON3 can then be installed. These screw terminals should be orientated so the wire entry faces the edge of the PCB. Mount the 14-way IDC box header (CON4) next. The location notch must face as shown and ensure that the header is pushed all the way down before soldering its pins. Fit the capacitors next, noting that the electrolytic capacitors have their longer (positive) leads through the holes marked “+”. The negative lead is marked with negative (–) signs down the capacitor can. Then solder the two small transistors (Q3 and Q4), which are both BC547s. siliconchip.com.au TO-220 package devices REG1, REG2 and diode D2 are mounted vertically with the mounting hole 22mm above the top of the PCB. REG2 will need pins 1, 3 and 5 bent more forward than pins 2 and 4 to fit the offset mounting holes. VR1 can be fitted now, as well as inductor L1. L1’s leads are inserted into the smaller PCB holes, while the inductor is secured in place with a cable tie that passes through the larger PCB holes provided. Insert the tie from the underside, then through the centre of L1 and back down through the second hole and tighten it up. Mosfets Q1 and Q2 are installed on the underside of the PCB. Bend the three leads for each Mosfet upward by 90°, 5mm from the bottom edge of the Mosfet body. Then insert the leads into the PCB from the underside, but do not solder them yet. Now place the PCB into the enclosure, sitting on the internal mounting corners. Mark where the Mosfets sit, including their mounting hole locations, then remove the PCB and place Fig.7: assembly of the front panel is straightforward, but be careful to orientate the switches and CON5 correctly, as described in the text. CON5 mounts on the back of the board, with the other parts on the front. Australia's electronics magazine August 2026  31 the silicone insulating washers under the Mosfets. Fig.8 shows how these Mosfets will be mounted, although we aren’t attaching them to the case just yet. Reinsert the PCB and adjust the Mosfets so they sit flat on the bottom of the case, on the silicone washers. Now solder the Mosfet leads on the top of the PCB, then remove the PCB and solder the leads on the bottom of the PCB as well. Winding the transformer Fig.9 shows the transformer winding details. The primary windings are made from 1mm diameter enamelled copper wire (ECW), while the secondary windings use 0.5mm diameter enamelled copper wire. The two windings for the primary are shown with different enamel insulation colours for clarity. There is no need to use different colours for your windings. Start with the primary windings. First, cut two 400mm lengths of the 1mm diameter ECW and remove the enamel from one end of each wire using fine emery paper or a hobby knife. Tin the wire ends and wrap one wire around pin 7 on the underside of the transformer bobbin and the other onto pin 8. Solder both close to the bobbin. The bobbin provides for the wire to be wrapped around behind the post before winding a couple of turns around the pin. Now close-wind seven turns of both wires Fig.8: this shows how Mosfets Q1 & Q2 attach to the board and the bottom of the case. Don’t forget the insulators. (side-by-side) until the windings reach the opposite end of the former. The winding direction does not matter as long as both wires are wound together. Using a multimeter set to measure resistance (ohms) or in continuity mode, find the wire that’s terminated to pin 7 and terminate its other end to pin 1 in the same way as before, ie, by stripping the insulating coating before wrapping it around the post and pin, then soldering it. The other wire end from pin 8 terminates at pin 6. Cover the windings in a layer of insulation tape. The secondary winding uses 0.5mm diameter ECW. Terminate one end to pin 4 and wind on 30 turns, then wrap a single layer of insulation tape over this winding and continue winding back over the first layer, in the same clockwise or anti-clockwise direction as before to complete 60 turns. Then, after adding another single layer of insulation tape, wind on another 30 turns in the same direction, for a total of 90 turns. Pass this wire back to pin 3 along the axis of the former. Cover it again with a layer of tape. Once wound, slide the cores into the former and secure them with the clips. These clips push onto the core ends and clip into lugs on the side of the bobbin. It is best not to install the transformer directly onto the PCB just yet. It can be temporarily wired up using some short lengths of 0.7mm diameter tinned copper wire or similar, connecting pins 6, 7, 8 & 1 for the primary plus pins 3 & 4 for the secondary to the corresponding PCB pads. This is so that it will be easier to remove and change the secondary windings should the output voltage not be within the desired range. More on this later. Now insert both IC1 and IC2 into their sockets, taking care to orientate them as shown on the overlay diagram. IC1 needs to be programmed with the firmware before use. The hex file is available from our website at siliconchip.au/Shop/6/3634 for those who have the equipment to program it themselves. Otherwise, you can purchase a programmed PIC from the Silicon Chip Online Shop. VR1 shaft extension VR1 requires a shaft extension to reach and pass through the enclosure lid, as shown in Fig.10. The shaft extension is made using 6mm diameter timber dowelling or several tapped nylon hexagonal spac- The Control and Main Boards for the Adjustable Ultrasonic Cleaner. 32 Silicon Chip Australia's electronics magazine siliconchip.com.au ers that are stacked together, plus a washer. These are held together with a 25mm-long M3 machine screw. If using the timber dowel, a flat will need to be filed at the top on one side for the knob to fit. The hexagonal nylon version already has a flat side to act as a key for the knob. We used a 40A dual-screw mains Earth wire connector as the bush to secure the two shafts together. The outer plastic covering can be removed by first removing the two screws. The inner metal part should then drop out. When securing this to the shaft of VR1, the potentiometer should first be set to its mid-position. Then the securing screws can be orientated toward the right edge of the PCB before tightening to the shaft. In this way, you can rotate VR1 fully in both directions without fouling the screws against the 1000μF capacitors. Fig.9: the transformer primary is bifilar wound in one layer, with thicker ECW, while the sole secondary is wound using thinner wire in three layers, with insulating tape in between each layer. Front panel control board assembly There are only a few parts on this PCB (coded 04105262), but be careful to mount them on the correct side. Most parts go on the top side, but the 14-way IDC box header (CON5) goes on the underside. Install the resistors first, then the 100nF capacitors. Insert the shorter side of the 16-way SIL (single in-line) header into the PCB and solder it in place, place the LCD screen over the pin header and mount it on two 6.3mm-long nylon spacers and secure it with two 12mm-long M3 machine screws & nuts. You can then solder the pin header to the LCD on the top side. Potentiometers VR2 and VR3 can be installed now, along with switches S1-S3. These switches need to be orientated correctly, with the anode and cathode for the internal LED of each placed as shown. The anode (A) and cathode (K) locations are marked on the PCB. Each switch will have a coloured marker (matching the colour of the LED) on the lower black part of the switch on the (K) side. Next, fit CON5 on the underside of the PCB, taking care to orientate it with the location notch as shown. Solder its pins from the top side of the PCB. Now the IDC cable needs to be made and plugged into this header. Fig.11 shows how the IDC cable is made using 14-way ribbon cable and two crimp connectors. The connectors can be clamped onto the cable by adding siliconchip.com.au Fig.10: there are two options for extending the shaft of VR1 to reach through the lid, using either a piece of timber dowel or several hexagonal tapped spacers. Either way, the inside of a double-screw wire connector is used to join it to the plastic pot shaft. Fig.11: the IDC cable is a little unusual in that pin 1 is swapped at each end, but the PCB connector orientations swap it back. The shaft of VR1 can be extended using a 35mm long timber dowel, as shown below. Or you can use a series of tapped spacers (see Fig.10). The IDC cable is made using 14way ribbon cable and two crimp connectors, see Fig.11 Australia's electronics magazine August 2026  33 a small piece of soft timber (eg, pine) over each side of the socket and compressing the lot with a G-clamp or bench vice (or use a specialised tool like Altronics Cat T1540). Make sure the socket orientations are correct before you compress them, with the locating tabs facing as shown in Fig.11. The remaining assembly work for this board is done after the enclosure lid has been prepared. The front panel drilling/cutting template (Fig.12) can be copied or downloaded from our website in PDF format (siliconchip. au/Shop/11/3561) and printed out at ‘actual size’. Attach it to the lid, ensuring the paper template is centred correctly. Next, mark and cut the holes. You can use a centre punch or nail and hammer to mark the centres before drilling. The holes for the power switch and LCD can be made by drilling a series of small holes around the perimeter, knocking out the piece and filing to shape until each fits correctly and is held in position firmly. The PCB is held to the lid using four M3-tapped 12mm standoffs/spacers plus a ~1mm-thick nylon washer to keep the PCB some 13mm back from the inside of the lid. These spacers go between the top side of the PCB and the inside of the lid. Front panel label The front panel label (Fig.13) can be made using overhead projector film, printing the label as a mirror image so that the ink will be between the enclosure and film when affixed. Use projector film that is suitable for your printer (either inkjet or laser) and affix it using clear neutral-cure silicone sealant. Roof and gutter silicone is suitable. Squeegee out the lumps and air bubbles before the silicone cures. Once cured, cut out the holes through the film with a hobby or craft knife. For other options and more detail on making robust labels, see the details on our website at siliconchip. com.au/Help/FrontPanels Two holes are required in each end of the box for the DC power cable gland and the ultrasonic transducer cable gland. Along the sides, 3mm holes are also required for attaching REG1, D2 and REG2 to the inside of the case. You can determine these positions by temporarily mounting the main PCB into the enclosure and marking where the holes need to be. Holes are also required in the base of the enclosure for Mosfets Q1 and Q2. You may have marked the positions earlier; if not, do this now. Drill these to 3mm. Lightly countersink these holes inside the enclosure, plus the ones for REG1, D2 and REG2 on the inside, to prevent the insulating washer from being damaged by a rough hole edge. You can use a large, sharp drill bit turned by hand. Attach Mosfets Q1 and Q2 using silicone insulating washers, plastic bushes and M3 machine screws with nuts, as shown in Fig.8. REG1 and REG2 similarly require an insulating bush and washer, but D2 can be directly mounted with a screw, as it has an insulated tab. Check that the metal tabs are isolated from the case using a multimeter on a high ohms setting. A reading above 1MW (ideally ‘open circuit’, often shown as “0L”) means that the isolation is good. Lower readings may be due to a punctured insulator or a short circuit to the case. Now wire switch S4 to the board using 5A-rated hookup wire, with heatshrink tubing over the soldered terminations. Once the other ends of the wires are secure in the screw terminals for CON2, use a cable tie to hold these wires firmly to the PCB using the larger holes in front of CON2. The cable tie passes through the board and then around the wires. Preparing the ultrasonic transducer There are many suitable 50W/60W 40kHz ultrasonic transducers available online. One such part is the Beijing Ultrasonic BJC-4050T- 45HS PZT4. Alternatives are at siliconchip.com. au/link/ab3g and siliconchip.com.au/ link/ab3h For the wire between the board and the transducer terminals, use mainsrated wiring that can handle at least 7.5A. Figure-8 wire or, preferably, a sheathed dual cable is suitable. The wire ends for the transducer can be soldered to solder lug eyelets and covered in heatshrink tubing. These can then be connected to the transducer terminals with M4 × 10mm machine screws, star washers and nuts. Left: Mosfets Q1 & Q2 are mounted with insulated washers behind them and bushes under the nut, as shown in Fig.8. Right: here is a close-up of VR1, which we’ve extended using multiple tapped nylon spacers, a washer and screw. 34 Silicon Chip Australia's electronics magazine siliconchip.com.au These terminals on the transducer are exposed and need to be protected within a housing to prevent accidental contact, as they are a shock hazard. The high-voltage AC can cause a nasty shock, but only if both contacts are touched. Touching one contact or the front face of the transducer will not cause a shock, since the transformer output is floating from the main circuit (don’t try this, though!). A suitable housing can be made using 50mm PVC DWV (drain, waste and vent) fittings. We used an end cap and an adaptor (with the smaller adaptor section cut off) to extend the length of the end cap to an overall outside length of 50mm. You could use the end cap and a short length of 50mm pipe instead of the adaptor. Wire entry is via a cable gland that is secured in the side or end of the end cap. Place the cable gland hole in a position allowing sufficient room for its securing nut inside. The transducer should be mounted within the DWV fittings using neutral-­ cure silicone sealant (such as roof and gutter sealant). Use just enough silicone to secure the transducer to the inside of the housing, around the outside of the lower bell-shaped section. Fully potting it in silicone will dampen the ultrasonic movements. The face of the transducer should be kept clear of the sealant. This is so that the transducer can be secured to the outside of the bath with an epoxy resin. Connect the ultrasonic driver cable to the PCB at CON3. Make sure there are no strands of copper wire emerging from the terminals that could short together. Testing Before testing, insert the M205 fuse into the clips, if you haven’t already done so. When ready, apply power to the circuit and check the main 5V supply between pins 20 and 1 of IC1, and between pins 4 and 8 of IC2. You should get a reading of 4.75-5.25V across these pin pairs. To properly test the board, you need to have the transducer attached to a suitable container that’s filled with a liquid like water. That’s because you need to check that the transformer is supplying the right voltage to achieve full power. Your transducer could differ from the one we have used, either by being a different type or just coming from a different batch. siliconchip.com.au Fig.12: the lid drilling and cutting details. This can be printed or copied at actual size and used as a template. The larger, rectangular holes can be made by drilling a series of smaller holes inside the perimeter, then filing the edges flat. Metal dishes with thin sheet metal will work best; there must be a flat side or base for the transducer to be attached. If you wish to mount the transducer on the side of the container, the height must be at least 75mm. One of the cleaning dishes we used was from Woolworths. It was an approximately 4L baking pan measuring 225 × 225 × 78mm. The base had a lift-out section that had to be glued in place to prevent leaks. We used roof and gutter silicone sealant for that. Alternatively, there are pans available from Nisbets (www.nisbets.com. Australia's electronics magazine au). They have shops in NSW, Vic, Qld and the ACT, but also sell by mail order. We recommend either the 150mm-deep ¼ gastronorm tray (capacity 4L) or the 100mm-deep ¼ gastronorm tray (capacity 3.7L). The transducer will need to be glued to a flat section on the outside of the container. We tested both side mounting and mounting on the base. The advantage of side mounting is that the container does not need to be raised on a stand to allow room for the transducer that’s mounted on the underside. August 2026  35 Our ultrasonic bath and completed Adjustable Ultrasonic Cleaner (before insulating the transducer). The front panel label is overleaf in Fig.13, you can also download it from siliconchip.com.au/ Shop/11/3561 Some containers are covered in a non-stick surface, which will need to be removed where the transducer mounts to allow glue to adhere (also slightly roughen the surface). Use wet-and-dry emery paper to clean up the area, then clean off any residue before gluing. J-B Weld two-part epoxy resin is recommended as the glue. Tape the transducer in position while it sets. The fluid used in the bath can be tap water with a few drops of detergent as a wetting agent. Other fluids that can be used include deionised water, alcohol (methylated spirits, isopropyl alcohol etc), acetone or similar solvents. The cleaning effectiveness is greatly enhanced when the fluid is warm. Filling it with around two litres of liquid is ideal for the power available from the ultrasonic transducer. Transformer tweaking The 90-turn secondary winding provided sufficient voltage for our test transducer to deliver between 32W and 39W of ultrasonic power into a 4L container filled with 2L of fluid. Any variation in the volume of fluid will affect the operation. More fluid will require a lower drive frequency. Additionally, the transducer impedance will be higher, meaning that more secondary transformer turns will be required for more drive voltage to maintain the power level. Less fluid will mean a higher resonance frequency and a lower drive voltage is required due to the transducer impedance being lower. It is recommended that the transformer windings be set up for use with 2L of fluid. Testing To test the Ultrasonic Cleaner Controller, power it up with the wattage pot wound fully anti-clockwise, then wind this up to show a voltage of around 5V. Press the Stop/Start button to initiate the ultrasonic drive, then adjust the frequency to find the resonance, where there is a peak in the displayed power. You may need to change the Span to find the resonance, including if the resonance is too close to the end of the frequency pot range. Ideally, find the span that allows the resonance to be near the middle of 36 Silicon Chip Australia's electronics magazine siliconchip.com.au the frequency pot adjustment range. Setting the precise resonance requires careful adjustment. Once the resonant frequency has been found, increase the power potentiometer setting. Check that it is possible to get over 30W when the voltage pot is wound up. If the power is over 30W at voltages lower than 10V, the transformer secondary should ideally have a reduced number of turns to avoid inefficient operation. If the power is not sufficient even with the voltage pot fully clockwise, more turns on T1’s secondary are needed. How many turns that need to be added or subtracted can be determined on a trial-and-error basis. If you get 36W, or at least over 30W with the pot wound fully clockwise, the existing number of secondary transformer windings are suitable. Note that the Ultrasonic Cleaner limits the input current to 3.3A, so if you wind up the power pot until that amount of current begins to flow, the voltage supplying the transformer will begin to reduce to maintain the 3.3A draw. Another unexpected effect that can occur is due to the current limit set by the LM2576 (IC2). This is guaranteed to be at least 3A, but could be more. If the current draw exceeds the LM2576’s limit, the output voltage will reduce, even without any change in the power/ voltage pot. So you may find that the voltage reading drops as you adjust the frequency to get maximum power at resonance. In that case, reduce the voltage pot setting and continue searching for the resonant peak. Then the pot can be rotated clockwise for more power, re-adjusting the frequency slowly to more precisely find the resonance point. The reason for the current limit is that the transducer impedance is lower on either side of resonance, so more current is drawn compared to at resonance. At resonance, the higher impedance allows for more voltage to be used without causing regulator overload. Current limiting is less likely when finding the resonance by winding it down from a higher frequency rather than winding it up from a lower frequency. As an example, in our prototype, using a 14V supply, 12V is shown on the LCD screen when the ultrasonic drive is on and the transducer is running at resonance. The power is 37W (so the current is 3.1A = 37W ÷ 12V). If the frequency is adjusted off-­ resonance, the voltage drops to 9.5V and the power shows as 31W. This means that 3.26A is flowing (31W/9.5V) and the regulator has reduced the output voltage from 12V to 9.5V to limit the current. Locking the frequency Locking and unlocking the frequency or span is done by first holding down the stop/start This photo shows how the two boards are joined once they are installed in the case. The insulator (shown at left) fits directly on top of the ultrasonic transducer. siliconchip.com.au Australia's electronics magazine August 2026  37 Silicon Chip Binders REAL VALUE AT $21.50* PLUS P&P Are your copies of Silicon Chip getting damaged or dog-eared just lying around in a cupboard or on a shelf? Can you quickly find a particular issue that you need to refer to? Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of S ilicon C hip . They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. H 80mm internal width H Silicon Chip logo printed in goldcoloured lettering on spine & cover Silicon Chip Publications PO Box 194 Matraville NSW 2036 Order online from www. siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *see website for delivery prices. 38 Silicon Chip Fig.13: this front panel label can be printed, laminated and attached to make the unit look nicer and identify the controls. button for over one second. The display then shows OPTION * = LOCK. While still holding the Stop/Start switch, press the down button to lock the Frequency setting (or unlock it if it was already locked). Similarly, pressing the up button while holding the Stop/Start switch locks or unlocks the Span setting. Using the timer Switch S3 starts and stops the Ultrasonic Cleaner. When pressed momentarily, it will start the output drive. An hourglass emptying and filling shows that the timer (and ultrasonic drive) is Australia's electronics magazine running. The value of the timeout, set by VR2, is shown on the LCD screen and drops every 7s or so as the time remaining reduces. Once the timer runs out, the transducer drive ceases, and the hourglass disappears. The timer setting from VR2 is shown instead. During the time-out period, the ultrasonic drive can be stopped by momentarily pressing S3 again. You can change the timeout period while the timer is running to a lower value and stop the timeout with the Stop/Start push button at any time SC during the timeout period. siliconchip.com.au