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This large and powerful Ultrasonic Cleaner is ideal for bulky items such as mechanical parts and delicate fabrics. Last month we described its features and explained how it works. Now let’s move on to building it and getting it going! Part 2 – by John Clarke Ultrasonic High Power Cleaner W e explained in the article last month that the measures 115 × 90 × 55mm. The overlay diagrams for both boards are shown in Figs.6 and 7. Start by fitting the resistors on both PCBs where shown. 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 0.1 SMD resistors mount on the top of the PCB, solder one end first and next check alignment before soldering the other end. Continuing with just the main PCB, fit diodes D1 and D2 and make sure that their cathode stripes face toward the top edge of the PCB as shown. ZD1 can also be mounted, oriented as shown. We recommend that IC1 and IC2 are mounted in sockets. Make sure that the notched ends face toward the lower edge of the PCB. The three PC stakes can also be fitted now; they are marked as GND, TP1 and TP2 (you can leave these off and probe the PCB pads later, if desired). Now mount REG1 flat onto the PCB with its leads bent down 90° to fit into the holes in the PCB. Secure it to the PCB using an M3 x 6mm screw and nut, then solder and trim Warning! its leads. Warning! Also mount the 3AG fuse The Thetransducer transducerisisdriven drivenatat100V 100VAC ACwhich whichisismore morethan than clips now, making sure that enough enoughtotogive giveyou youaashock. shock.Touching Touchingboth bothofofthe thetranstransthey have the correct orientaducer ducerterminals terminalsduring duringoperation operationwill willgive giveyou youan anelectric electric tion, with the end stops toward shock, and it will be worse if your hands are wet. You must shock, and it will be worse if your hands are wet. You must the outside of the fuse. enclose enclosethe thetransducer transducerininthe thePVC PVChousing housingdescribed describedinin It is a good idea to insert this thisarticle articleand andonly onlyrun runititwhen whenso soenclosed enclosedand andattached attached the fuse before soldering the totoaabath bathfilled filledtotothe thecorrect correctlevel levelwith withcleaning cleaningfluid. fluid. clips in place to ensure that microcontroller in the Ultrasonic Cleaner uses three MOSFETs and a step-up transformer to produce around 100V AC to drive an ultrasonic transducer at just under 40W. This transducer is attached to the side of a vessel containing cleaning liquid and the objects to be cleaned. You select a power level and a time, and it does the rest. The electronic components are mounted on two PCBs which are housed in a diecast aluminium box. The lid of the box has all the controls and the indicator LEDs. The only external wiring is for 12V DC power to the unit (it draws around 4A at full power) and one twin lead which emerges from the box via a cable gland and goes to the transducer that’s glued to the liquid vessel. Building the Ultrasonic Cleaner isn’t too difficult. The main steps are winding the transformer, soldering the components to the PCBs, drilling the case, mounting the parts in the case and wiring it up. We shall now describe all the necessary steps in detail. PCB construction The Ultrasonic Cleaner is built using two PCBs available from the PE PCB Service. The main PCB (code 04105201) measures 103.5 × 79mm; and the smaller front-panel PCB (code 04105202) measures 65 × 47mm. The assembled PCBs are housed in a diecast box which 34 Practical Electronics | October | 2021  SILICON CHIP                     Fig.6: fit the components to the main Cleaner PCB as shown here. Watch the orientation of the diodes, ICs, electrolytic capacitors and box header CON4. MOSFETs Q1 and Q2 are mounted on the underside, with their leads coming up through six pads next to transformer T1. Two holes in the PCB give access to their tabs, so that they can be mounted to the bottom of the case for heatsinking. This final version PCB is slightly different to the photo of the early prototype at right. the fuse is aligned in the clips and that the clips are oriented correctly. Ideally, the fuse clips should also be soldered on the top of the PCB on one side of each clip, to minimise the connection resistance. The DC socket (CON1) and the 2-way pluggable terminal block socket (CON2) can then be installed. Take care with CON2’s orientation; insert the plug into the socket before soldering the socket. This will ensure the orientation is correct, as the screws need to face towards the fuse so that the assembly will fit on the PCB. Also fit the 2-way screw terminal (CON3), with the wire entry toward the edge of the PCB. Mount the 14-way IDC box header (CON4) now. Make sure the notch is oriented as shown and it is pushed all the way down before soldering its pins. Fit the capacitors next, noting that the electrolytic capacitors must be oriented with the longer positive leads through the holes marked ‘+’. Then solder the three small transistors (Q3-Q5), which are all BC547s. MOSFET Q6 (the SUP53P06-20) is mounted vertically with the mounting hole 22mm above the top of the PCB. MOSFETs Q1 and Q2 mount 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 the silicone insulating washers at these locations. 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 that they sit flat on the bottom of the case, on the silicone washers. Now solder the leads on the top of the PCB. Then remove the PCB and solder the leads on the bottom of the PCB as well. Similarly, for Q6, solder the leads on both sides of the PCB. 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 winding uses 0.63mm diameter enamelled copper wire. Start with the primary windings. First, cut two 400mm lengths of the 1mm 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. Now close-wind seven turns of both wires (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. Cover the windings in a layer of insulation tape. Pass the wires back along the spine of the former. Using a multimeter on the ohms setting, find the wire that’s terminated to pin 7 and terminate its other end to pin 12 in the same way as before. The other wire end terminates at pin 7. Cover the windings in a layer of insulation tape. SILICON CHIP Practical Electronics | October | 2021 Fig.7: IDC header CON5 mounts on the back of this front panel board, while the LEDs, switches and potentiometer VR1 protrude through holes in the front panel. Make sure that VR1’s body is grounded via the pads provided and also check that the LEDs are all oriented as shown. 35 Fig.9: follow these transformer winding instructions carefully, to make sure that your finished transformer has the correct phasing and turns ratio. Fig.8: this is how the MOSFETs are mounted to the board and the case (for heatsinking). Ensure that the tabs are fully isolated from the case before powering the Cleaner up. Initially, the MOSFETs can be attached to the outside of the box for testing, then later moved to the inside (the mounting method is the same either way). The secondary winding uses the 0.63mm ECW. Terminate one end to pin 3 and wind on 29 turns (the direction does not matter). Then wrap a layer of insulation tape over this winding and continue winding back over the first layer, in the same direction as before (clockwise or anticlockwise) to complete 57 turns. Terminate this to pin 4. Once wound, slide the cores into the former and secure with the clips. These clips push on to 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, between pins 3, 4, 7, 8 and 12 of the transformer and the PCB pads for those pins. This is so that it will be easier to change the secondary windings, should the ultrasonic transducer require fewer or extra turns. More on this later. Now insert both IC1 and IC2 into their sockets, taking care to orient them as shown on the overlay diagram. First wind the primaries using 1.0mm diameter enamelled copper wire. Using bifilar winding, wind 2 x 7 turns in a single layer. One winding starts from pin 7 and ends at pin 12; the other winding starts from pin 19 and ends and pin 7. When both windings are terminated, cover them with a layer of plastic insulating tape. Then wind the secondary, using 0.63mm diameter enamelled copper wire: 57 turns in two layers, starting from pin 4 and ending at pin 3. Place one layer of plastic insulating tape over each layer. Print it and attach it to the lid, ensuring that the paper template is centred correctly. Mark out and cut the holes. The hole for the power switch can be made by drilling a series of small holes around the perimeter, knocking out the piece and filing to shape until the switch fits and is held in position firmly. Break off the locating spigot on the potentiometer and mount the potentiometer onto the lid. Place the washer between the pot and lid, with the nut on the outside of the lid. Also attach the switches, with one nut on either side of the lid. Switch orientation doesn’t matter. Insert the LEDs into their pads from the top side of the PCB, taking care to orient them all with the longer lead (anode) going into the pads marked ‘A’. Do not solder the LEDs in yet. Place the PCB onto the switch terminals and solder them in place. Scrape off the coating on the pot body where the two mounting PC stakes are to solder to the pot body (don’t inhale the dust). This allows the solder to wet the pot body for a good solder joint. Solder the PC stakes to the pot terminals after bending the pot terminals over to meet the PC stakes. Front panel control board assembly There are only a few parts left on this PCB, but be careful to mount them on the correct side. Most parts go on the top side, but the 14-way IDC transition header (CON5) goes on the underside. Fit CON5 first, taking care to orient it with the pin 1 triangle as shown in Fig.7. Solder from the top side of the PCB. Now the IDC cable needs to be attached to this header. Fig.10 shows how the IDC cable is arranged in CON5. The wire can be secured by adding a small piece of soft timber (eg, pine) over the soldered pins on the PCB and another piece of timber on the other side of the PCB, and compressing the lot with a G-clamp or bench vice. The other end of the IDC cable goes to the socket, again taking care to orient the socket correctly with the locating tab as shown. Compress as before, with protective timber and a G-clamp or bench vice (or use a specialised tool like AlPIHC NOCILIS tronics Cat T1540). The resistors can also now be installed, if you haven’t already. Also insert the five PC stakes from the top side of the PCB for the potentiometer mounting and connections, and fit the 100nF capacitor. The remaining assembly work for this board is done after the enclosure lid has been prepared. Cut the potentiometer shaft so that it is 12mm long Fig.10: this is how the from the threaded boss, or to suit the knob used. ribbon cable connects to the front panel board. The front panel label (Fig.11) shows the posi- If CON4 has been fitted tion of the LEDs, power, start and stop switches correctly to the main board, and the potentiometer on the lid. This label then it should plug straight in. Note that the ‘IDC transition header’ can also be downloaded as a PDF file from the used for CON5 on the front panel board is captive, ie, there is no October 2021 page of the PE website. socket. Its pins are soldered directly to the PCB. 36 Practical Electronics | October | 2021 The finished controller shown ‘opened out’, albeit with the ribbon cable disconnected from CON4. The LEDs can now be pushed up into the holes on the lid and soldered in place, then trimmed. The PCB is held in position by the switches and potentiometer. There is no need for extra support. If you absolutely must, you could attach 15mm-long standoffs to the corner holes. Front panel label The front panel label 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 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. Two holes are required in the side of the box for the DC power connector and the ultrasonic transducer lead, plus one for mounting Q6. The locations and sizes are shown in Fig.12. Holes are also required in the base of the enclosure for mounting MOSFETs Q1 and Q2. You should have marked the positions earlier; drill these to 3mm. Lightly countersink these holes inside the enclosure, plus the one for Q6 on the side, to prevent the insulating washer from being damaged by a rough hole edge. Also lightly countersink the holes for Q1 and Q2 on the outside of the enclosure. This is so these MOSFETs can be mounted temporarily on the outside of the enclosure for testing purposes. This way, you will have better access to the PCB for testing and fixing any problems without having to remove it from the box. Fit the four M3 × 9mm standoffs to the underside of the PCB using 6mm screws, then attach MOSFETs Q1 and Q2 using silicone washers, insulating bushes and M3 screws and nuts, as shown in Fig.8. Practical Electronics | October | 2021 Check that the metal tabs are isolated from the case using a multimeter on a high ohms setting. A reading in the megohm region means that isolation is good. Lower readings indicate a shorted connection to the case. Wire switch S1 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, plug it into the CON2 socket. Preparing the ultrasonic transducer There are many suitable 50W/60W 40kHz ultrasonic transducers available online – see last month’s parts list for a device readily available in the UK. (Depending on your location / shipping costs, these sellers are also worth trying: https://bit.ly/pe-oct21-us1 and https://bit.ly/pe-oct21-us2) The wiring can be soldered to the transducer terminals; 0.75mm2 figure-8 wire or sheathed dual cable is suitable. The 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 100V 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. Howevver, do not rely on this to protect you! A suitable housing can be made using 50mm PVC DWV (Drain, Waste and Vent) fittings. We used an end cap and a screw thread adaptor (with the screw thread 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 of the end cap. Place the cable gland hole in the side of the end cap, allowing sufficient room for the nut inside. The adaptor or pipe will require an area removed 37 Fig.11: the lid/front panel artwork for the Ultrasonic Cleaner, which also serves as the lid drilling/cutting template. You can download this as a PDF file from the October 2021 page of the PE website, print it and optionally laminate it (or print onto adhesive label paper – see the text for more details). with a file so that it clears the gland nut when inserted into the end cap. The terminals on the transducer will need to be bent over at their ends to fit into the housing. The transducer should be mounted within the enclosure using neutral-cure silicone sealant (such as roof and gutter sealant). Use just sufficient 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 a little. 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 which could short out. The other ends of this cable connect to the ultrasonic transducer. Testing Before testing, insert the 3AG fuse into the clips if you haven’t already done so. If you’re powering the unit from a battery, or your power supply doesn’t already have a DC barrel plug to match the socket on the Cleaner, attach the plug to the end of the power supply wires. 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 for IC2. You should get a reading of 4.75-5.25V across these pins. When first powered up and after the Start switch is pressed, the Ultrasonic Cleaner will run the calibration for the transducer. While you can do that now, as long as the transducer is attached, the calibration will be incorrect. This is because the impedance of the transducer differs between when unloaded and loaded. When loaded (by attaching to the bath with fluid), the impedance is higher, so if you run it now, it will need to be re-calibrated later. The procedure to do that is described in the Calibration section below. Once calibrated, the power level will be shown, and the power LED will light once the transducer is being powered at the set level. If no transducer is connected, the power LED will go out momentarily and one or two level LED(s) will light. Then the level LED or LEDs will extinguish, and the power LED will relight. No calibration will occur. To properly test the board, you need to have the transducer at least temporarily attached to a suitable vessel, filled with a liquid such as 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. Diagnostics We have included a diagnostic display for the power level so that you can check whether your transducer is delivering full power. With the unit powered up and the transducer connected and attached to a bath, set the power level to 100%. The display will indicate if the transducer can or cannot deliver full power. If it can, the 100% LED will stay lit. If the transducer cannot deliver that power level, the power will begin to reduce automatically until it shows what can actually be produced by the transducer. If this happens to you, you may be able to achieve full power by removing water from the bath. However, this may leave you with insufficient water for practical cleaning. If you decide to lower the water level, make sure to re-run the calibration procedure (see below) before testing for full power again. The alternative to reducing the water level is to add more turns on the secondary of transformer T1. This will increase the transducer drive voltage to allow the extra Fig.12: only three holes need to be drilled in the side of the case, two 12mm and one 3mm in diameter. The 3mm hole is for mounting the tab of MOSFET Q6, while the others are for the DC socket and transducer cable gland. 38 Practical Electronics | October | 2021 unit, hold down the Stop switch, press the Start switch and then release both. This should be done while the transducer is loaded, ie, attached it to the fluid-filled bath. Running the transducer unloaded will cause a large current flow to the transducer due to its lower impedance. While the circuit prevents excessive current by switching off, it is still a good practice to avoid driving the transducer except when under load. During calibration, the resoHere’s the transducer (left) and mounted nance of the transducer will be inside our ‘plumber’s special’ DWV PVC ‘case’. found and stored in non-volatile This photo was taken before we secured the Flash memory. This means that transducer to the ‘case’ with neutral-cure the unit doesn’t have to find the silicone sealant. resonance frequency each time the Cleaner is used. At the beginning of the calibration procedure, all five power to be delivered. How many turns need to be added level LEDs will light, and then they will switch off. See the can be determined on a trial-and-error basis. Once full power is possible, the transducer may not be troubleshooting section if you are experiencing problems able to be driven at the very low power levels. This can with the calibration. be determined by setting the level to the lowest setting. If this low power is not possible, the level display will Using the timer increase by itself to a higher level, indicating the lowest When cleaning parts, set the timer for the maximum duration you want. The time can be changed while the Cleaner power level available. Note that the over-current indication (the left, middle is running, and it will use the new time, providing that it and right level LEDs flashing simultaneously) may show is longer than what has already transpired. Setting to a time setting to less than what has already instead. If so, that suggests you have too many turns on the transformer secondary (see the Troubleshooting sec- transpired will cause it to stop immediately, as will pressing the Stop button. tion below) The lowest power level available will depend on the steepness of the transducer’s power/frequency curve. This Troubleshooting is a measure of how sharply the power drops away when If you are having difficulty achieving calibration, you can run off-resonance. Steep sides on the power/frequency curve a more comprehensive diagnostics routine that will provide for the transducer will mean that it can be driven at the more information. This is initiated by switching the power off, waiting 10 seclowest power. In contrast, other transducers with shallower curves onds, then pressing and holding the Start and Stop switches might only be able to be operated one level above the together while switching on the power. The diagnostics routine will start, as indicated by all five level LEDs lighting up. minimum (ie, 20% rather than 10%). In this mode, the frequency to the ultrasonic transducer can be manually adjusted using the timer potentiometer (VR1). The Finalising construction Once you are happy with the available power range, detach frequency is 40kHz when the timer pot is set midway and can the PCB from the case. Transformer T1 can now be perma- be varied from 37.6kHz to 42.4kHz by rotating VR1. Further frequency changes can be made by setting the pot nently installed on the PCB, rather than via short lengths either fully anticlockwise or fully clockwise and pressing the of connecting wire. Before fitting the PCB in the box, disconnect the ultrasonic driver cable (making sure that the power is off!), then feed its cable through the cable gland, the hole in the enclosure and the gland securing nut, then re-connect it to CON3. Make sure there are no strands of copper wire emerging from the terminals which could cause a short. The three MOSFETs are attached to the inside of the enclosure using the silicone washers and insulating bushes, M3 screws and nuts. Refer to Fig.8 (the same as before, but this time on the inside). Once again, check that the metal tabs are isolated from the case using a multimeter set for reading ohms, using the same procedure as before. The PCB is secured to the enclosure using the two supplied screws. Insert the supplied Neoprene seal in the lid channel and cut it to length before attaching the lid using the screws provided. Finally, stick the four rubber feet to the base. Calibration As mentioned earlier, calibration happens automatically the first time you press the Start switch. To re-calibrate the Practical Electronics | October | 2021 Here’s the transducer glued to the cleaning bath (in this case a stainless steel cooking tray). We used J-B Weld, a two-part epoxy which we find works better than any other. 39 Another view of the PCBs sitting inside the diecast box – one mounted on the lid. Here you can clearly see one of the two MOSFETS with its mounting screw accessible through the hole in the PCB. Don’t forget the insulating washer and bush underneath! Start switch. When holding the pot fully anticlockwise and pressing the Start switch, the frequency will drop by about 540Hz so that overall adjustment range is 540Hz lower, ie, 37.06-41.86kHz rather than 37.6-42.4kHz. You can reduce this further in 540Hz steps to a minimum of 34.88kHz with the pot fully anticlockwise, by pressing the Start switch repeatedly with VR1 at its fully anticlockwise position Similarly, the frequency range can be increased in 540Hz steps by holding the pot fully clockwise and pressing the Start switch. The maximum frequency can be increased up to 45.45kHz by doing this repeatedly. You can monitor the drive frequency by connecting a frequency counter or meter at TP2. You can monitor the current draw with a voltmeter at TP1. You don’t really need to know the frequency, so if you don’t have the means to measure this, it is not critical. JTAG Connector Plugs Directly into PCB!! No Header! No Brainer! Our patented range of Plug-of-Nails™ spring-pin cables plug directly into a tiny footprint of pads and locating holes in your PCB, eliminating the need for a mating header. Save Cost & Space on Every PCB!! Solutions for: PIC . dsPIC . ARM . MSP430 . Atmel . Generic JTAG . Altera Xilinx . BDM . C2000 . SPY-BI-WIRE . SPI / IIC . Altium Mini-HDMI . & More www.PlugOfNails.com Tag-Connector footprints as small as 0.02 sq. inch (0.13 sq cm) 40 The most critical measurement is the current readings at TP1. Adjust VR1 to find the resonance point, where the current is at a maximum. For the transducer to be able to deliver full power, the current measurement at TP1 needs to be 4.2V just below or above resonance. 4.2V equates to 300mV across the 0.1Ω resistors, so a 3A current. With a 12V supply, this represents a 36W power delivery. If there is a current overload and the voltage at TP1 goes above 4.8V, the transducer drive will be cut off. This is to limit power applied to the transducer to a safe level. Overload is indicated by the outside and centre LEDs on the level display lighting. The drive is restored momentarily every two seconds to check the current. Adjust the potentiometer to restore continuous drive. You can also press the Stop switch to switch off the transducer. To resume, you need to switch off the power and reenter the diagnostics routine as described above. As mentioned previously, if at the resonance there is an insufficient voltage at TP1, then you will need more secondary turns on the transformer (or take water out). The correct number of turns or amount of water is when the TP1 voltage is close to 4.5V at resonance. This allows some leeway in frequency control to achieve 4.2V at TP1, for 36W into the transducer when slightly off-resonance. If the TP1 voltage when approaching resonance is too high (ie, above 4.5V), reduce the number of secondary turns or use more water in the bath. Reproduced by arrangement with SILICON CHIP magazine 2021. www.siliconchip.com.au Practical Electronics | October | 2021