Fullscreen HTML5Med Res (??MB)HTML4

Part 1 by John Clarke Background source: https://unsplash.com/photos/a-person-in-yellowgloves-and-blue-gloves-cleaning-a-floor--dc38HdQR1M Ultrasonic Cleaner adjustable This 40W Ultrasonic Cleaner is fully adjustable for frequency, power and duration. You can also select the shape and size of the cleaning container you use. It’s powered from a 12-15V DC supply. Ultrasonic Cleaner Controller is ideal reach the small apertures that are usuFor more delicate parts, the power Tlery,hisforornaments, cleaning items such as jewel- ally the most important areas to clean. can be reduced to prevent damage to mechanical parts and An ultrasonic cleaner makes this the items being cleaned. small areas of delicate fabrics. Cleaning fuel injectors, a carburettor, or any other intricate parts is a messy and time-consuming task, requiring soaking them in harsh solvents such as petrol, kerosene, or degreaser and then scrubbing them with various brushes. It is a difficult and tedious task and often does not task so much easier. Just place the components in a solvent bath, press a button, then come back later to remove the parts in sparkling clean condition. It will even clean internal areas! It uses a high-power piezoelectric transducer and an ultrasonic driver to release the dirt and grime with ultrasonic energy. Fig.1: in the ultrasonic transducer we’re using, two piezoelectric (ceramic) discs are sandwiched between the two halves of the body, with electrodes to allow a voltage to be applied across the piezo elements. The compression of the piezoceramics due to the tension from the bolt holding the whole thing together is critical to prevent early failure from the ultrasonic vibrations. 28 Silicon Chip Our previous High Power Ultrasonic Cleaner in September and October 2020 (siliconchip.au/Series/350) was an automatic unit that found the transducer resonance itself. Manual operation was possible, but it wasn’t as easy as this latest offering. Because this one has adjustable power and doesn’t rely on automatically Fig.2: the frequency vs power curve for the transducer. Most transducers with a nominal 40kHz resonance should be similar, but the exact frequency of the peak will vary, as will the steepness of the slopes. Hence, our Cleaner allows you to adjust the frequency to find the peak, from 33.683kHz to 46.859kHz. Australia's electronics magazine siliconchip.com.au Features » » » » » » » » » Background source: https://unsplash.com/photos/frostedwater-with-bubbles-_LHf-WzBYpo Ultrasonic cleaning at up to 40W Screen shows frequency, span, timer, voltage and wattage Manual frequency control Timer from seven seconds to 30 minutes Operates from 12-15V DC at up to 4A Reverse supply polarity protection Over current protection Ultrasonic standing wave minimisation Can use a variety of cleaning bowl sizes and shapes from 2.5L to 4L Specifications » » » » » » » » » Frequency reading: 1Hz resolution, ±3% at 25°C Frequency adjustment: 16 spans from 33.683kHz to 46.859kHz (see Table 1) Fine frequency adjustment in 128 steps of about 37Hz (for Span 0) to 44.5Hz (for Span F) Voltage supplied to T1’s primary: from 1.23V to 1.4V below the input supply, displayed with a 100mV resolution Power readings: 1W resolution Current power limiting: 3.3A (40W with 12V at the transformer primary) Power delivery to 2L of water: 32W with a 12V supply, 39W with a 13.8V supply Timer: seven seconds to 30 minutes in approximately seven second steps Standing wave reduction: ultrasonic drive is switched off every 14s for about 1ms with variation to ensure a near 180° phase change each time. finding the resonant frequency, it’s less fiddly to get up and running. As a bonus, this latest Ultrasonic Cleaner Controller provides much more information than the previous version by having a two-line, 16-­ c olumn liquid crystal display (LCD) screen to convey useful readings, allowing for an easy setup. How does it work? A metal container is filled with a solvent, de-ionised water, or normal hot water with a detergent or wetting agent. The ultrasonic transducer agitates the contents of the bath. At higher power levels, the ultrasonic wavefront causes cavitation, creating bubbles which then collapse, as shown in Fig.3. As the wavefront passes, normal pressure is restored and the bubble collapses to produce a shockwave. This shockwave helps to loosen particles from the item being cleaned (Fig.4). The size of the bubbles depends on the ultrasonic frequency; they are smaller with higher frequencies. We are using the commonly available bolt-clamped Langevin ultrasonic transducer, depicted in Fig.1. It comprises piezoelectric discs sandwiched between metal electrodes. siliconchip.com.au The central bolt not only holds the assembly together, but is critical in ensuring the piezo elements are not damaged when being driven. The bolt is torqued to a predetermined tension and locked (thread glued) in place to prevent it loosening. The bolt tension ensures the piezo discs always remain in compression even while they are operating, preventing the discs from breaking apart. When a voltage is applied to the piezoelectric discs, forces are generated by the piezo elements that move the two metal ends closer together and then further apart at the ultrasonic drive rate. Our Ultrasonic Cleaner drives the piezo transducer at close to its nominal 40kHz resonant frequency. Fig.2 shows the power applied versus frequency for the particular ultrasonic transducer we are using. It claims to have a resonant frequency of 40kHz ±1kHz. When under load, resonance is lower; we found that resonance dropped by a couple of kilohertz. The transducer drive frequency needs to be adjusted to produce the required power level. A small change in frequency from the resonant point will reduce the power quite markedly. Australia's electronics magazine Figs.3 & 4: the sound waves produced by the Ultrasonic Cleaner rapidly create and destroy bubbles in the liquid. When they collapse, they generate localised shockwaves. This ‘cavitation’ stirs up the solvent layer that’s in contact with the dirt, grease and grime, helping to break it up and more rapidly dissolve it away. You can do this by hand – it’s called scrubbing – but it’s a tedious job, and it’s hard to get into nooks, crannies and internal spaces in the parts being cleaned! July 2026  29 The Adjustable Ultrasonic Cleaner is built using two PCBs; the Main Board shown at left, and the Control Panel Board below. Switches S1-S3 have a coloured marker near their cathode pin. Image Source: Jaycar Additionally, the transducer impedance varies depending on the load. So when operating in free air, the impedance is much lower compared to when the transducer is driving a bath full of cleaning fluid. Another factor affecting the power delivered is the voltage applied to the ultrasonic transducer’s driver transformer. Higher voltages produce a higher power output. Presentation The Ultrasonic Cleaner controller fits in a diecast aluminium enclosure with three knobs, three pushbutton switches, a power switch and the LCD screen. Two knobs are for the timer setting and the frequency adjustment. Pushbutton switches are for changing the frequency span selection up and down to select between 16 options, and the start/stop of ultrasonic drive. The 16 spans allow the frequency to be adjusted between 36.140kHz to 46.859kHz. The frequency knob allows for finer frequency adjustment within the range of each span. Below one minute, the timeout is shown in seconds, while above one minute, the timeout is shown in minutes and decimal minutes in 0.1m steps. The third adjustment knob is for the voltage applied to the transformer that drives the ultrasonic transducer. It can be adjusted from 1.23V to around 11-12V depending on the input voltage. This allows the ultrasonic power delivery to be adjusted. This control is labelled as ‘Power’ since that’s what it affects. The transformer voltage and delivered power are shown on the LCD 30 Silicon Chip screen, along with the frequency, span and timeout. Circuit details The Ultrasonic Cleaner circuit is shown in Fig.5. It is based around a PIC16F1459 microcontroller (IC1) that controls the two Mosfets (Q1 & Q2) driving the primary windings of transformer T1 in an alternating fashion. T1 produces a stepped-up voltage of around 150V AC (RMS) to drive the ultrasonic transducer. IC1 also drives the LCD screen, monitors the Timer potentiometer (VR2), Frequency potentiometer (VR3) and switches S1-S3. At the same time, it measures the current flowing through Mosfets Q1 and Q2 at its AN3 analog input (pin 3) via amplifier IC2b and the voltage applied to the transformer (T1) at its pin 8 analog input (AN8) via a voltage divider. IC1 is powered from REG1, a 5V regulator that is supplied input voltage via diode D1, which provides reverse polarity protection. Adjustable transformer supply REG2 is an LM2576 adjustable regulator. It is supplied with 12-15V from CON1 via power switch S4 and 4A fuse F1. Diode D3 provides reverse polarity protection by conducting if the supply voltage goes negative. The fuse then blows, preventing damage to REG2. Australia's electronics magazine The LM2576 is a switch-mode stepdown regulator. It has an internal transistor that switches on to charge inductor L1 via the load and output capacitors. When it switches off, diode D2 provides a path for the inductor current to continue to flow to the load. The duty cycle of the internal transistor being on compared to being off determines the output voltage. Feedback is applied to pin 4 of REG2, and the duty cycle is adjusted by the regulator to maintain 1.23V at this pin. The output voltage can thus be adjusted by varying the resistance of the top divider resistance, which includes 100kW potentiometer VR1. Ideally, a 50kW potentiometer should be used, but 100kW potentiometers are more common, so we shunt it with a 100kW fixed resistor. siliconchip.com.au Fig.5: the complete Cleaner circuit diagram. Microcontroller IC1 drives Mosfets Q1 & Q2 alternately, causing an AC current to flow in T1’s primary. T1 steps up the voltage in the primary to around 150V AC in the secondary for driving the transducer at 40W. REG2 allows the primary voltage to be adjusted, controlling the output power, while op amp IC2b helps to provide current monitoring feedback and IC2a allows IC1 to reduce REG2’s output to prevent overload. That fixed resistor should be omitted if a 50kW potentiometer is used. A 22kW resistor connects to the divider from IC2a’s output; this op amp buffers the analog output from pin 7 of IC1. This allows IC1 to control the output voltage to some extent, limiting power to the ultrasonic transducer. More on this later. REG2’s output provides voltage to transformer T1’s primary winding. Two 1000μF 25V low-ESR capacitors are used to provide storage of voltage from the switch-mode supply and maintain a low source output for the siliconchip.com.au transformer. These capacitors also smooth the supply ripple from REG2. REG2’s output can’t go as high as its input; there is a voltage drop of about 1.4V. So a 12V output cannot be produced if the input voltage is 12V. Typically, the maximum output voltage with a 12V input is 10.6V at 3A. Similarly, with a 13.8V input, a maximum of 12.4V can be produced at 3A. Transformer driving A complementary waveform generator within IC1 is used to drive Mosfets Q1 & Q2 in push-pull mode. The Australia's electronics magazine transformer (T1) is centre-tapped to allow this type of drive, with the supply from REG2 applied to the centre tap. IC1’s pulse-width modulation (PWM) generator includes an adjustable dead time, allowing time for one Mosfet to switch off before the other Mosfet switches on. IC1’s RC5 and RC4 digital outputs provide the complementary gate drive signals for Mosfets Q1 & Q2. Since these outputs only swing from 0V to 5V, we are using logic-level Mosfets. Standard Mosfets require gate signals of at least 10V for full conduction, but July 2026  31 logic-level Mosfets will typically conduct fully at 4.5V, or sometimes at even lower voltages. With the IPP80N06S4L-07 Mosfets we are using, the typical on-resistance (between drain and source) is 7.9mW at 40A with a 4.5V gate voltage. They are rated at 80A continuous and include over-voltage transient protection that clamps the drain-to-source voltage at 60V. Mosfets Q1 & Q2 are driven alternately and these drive the separate halves of the transformer primary of T1, which has its centre tap connected to the adjustable supply. When Mosfet Q1 is switched on, its drain goes low (to 0V and current flows in its section of the transformer primary winding. Q1 remains on for less than 12.5μs (assuming a 40kHz operating frequency) and is then switched off. Both Mosfets are off for two microseconds before Q2 is switched on. Q2 then draws current through its section of the T1 primary winding and remains on for the same duration as for Q1. Both Mosfets remain off again for 2μs before Q1 is switched on again. The gap when both Mosfets are off is the dead time, which allows for the fact that they don’t switch off immediately when their gates reach 0V (discharging the gate capacitance also takes time). Scope 1 shows the gate drives to Q1 (top yellow trace) and Q2 at the lower cyan trace when running at 40kHz. The two Mosfets are each off during the 2μs dead time period and switched on for around 10.2μs. The vertical cursors indicate the dead time. Without dead time, the two Mosfets would both be on together for a short duration. This would cause massive short-circuit current spikes, overheating the Mosfets and also drawing large current spikes from the supply filter capacitor and DC power supply. The inductance and resistance of the transformer primary would limit this to some extent, but it’s still best to avoid it. The alternate switching action of the Mosfets generates an AC square wave in the secondary winding of transformer T1. With a turns ratio of 12.8:1 (assuming a 90-turn secondary and 7-turn primary) and 12V DC at the primary, the secondary winding delivers about 150V to the ultrasonic transducer. The waveform applied to the ultrasonic transducer is shown in Scope 2, with 12V at the transformer primary and 35W delivered to the transducer, both values shown on the LCD screen. The voltage applied to the ultrasonic transducer shown in the yellow trace is around 150V peak (on average; it varies a bit). The cyan trace is the measured current scaled by 1.4V/A. So the 4.07V current reading value equates to 2.9A. Table 1: Typical frequency range adjustment within each span Span # Centre frequency Minimum Maximum 0 36.140kHz 33.683kHz 38.409kHz 1 36.580kHz 34.123kHz 38.665kHz 2 37.040kHz 34.520kHz 39.177kHz 3 37.500kHz 34.980kHz 39.689kHz 4 37.970kHz 35.387kHz 40.458kHz 5 38.460kHz 35.877kHz 40.970kHz 6 38.960kHz 36.314kHz 41.482kHz 7 39.470kHz 36.761kHz 41.994kHz 8 40.000kHz 37.291kHz 42.506kHz 9 40.500kHz 37.728kHz 43.018kHz A 41.138kHz 38.366kHz 43.530kHz B 41.660kHz 38.825kHz 44.299kHz C 42.250kHz 39.415kHz 45.067kHz D 42.860kHz 39.962kHz 45.579kHz E 43.418kHz 40.520kHz 46.091kHz F 44.117kHz 41.156kHz 46.859kHz 32 Silicon Chip Australia's electronics magazine With 12V at the primary of the transformer, the power is 34.9W (2.9A × 12V). Standing waves Running the Ultrasonic Cleaner at a constant frequency near resonance is efficient, since the impedance of the transducer is almost purely resistive under those conditions. However, this is not ideal for minimising standing waves within the cleaning bath. Standing waves can build in strength while the frequency remains constant. These waves are caused by reflections from the parts being cleaned and the tank walls being in phase. This can damage delicate parts. To avoid standing waves, the drive is stopped every 14s for about 1ms with variation to ensure a near-180° phase change each time. This out-of-phase change attempts to calm the standing waves. Additionally, our Ultrasonic Cleaner Controller can reduce the power so it can be used with delicate parts and parts that have delicate sections within them, especially thin-walled cavities. The power is reduced by lowering the voltage applied to the driver transformer. Over-current protection Overcurrent protection for the Mosfets is provided in two ways. Both rely on current detection via the voltage across the 0.1W resistors between the sources of Q1 and Q2 and ground. The first method uses NPN transistors Q3 and Q4. These have their base-emitter junctions connected across those 0.1W current-­sense resistors. The protection starts when the voltage across the 0.1W resistor exceeds about 0.5V, ie, more than 5A through either Q1 or Q2. The associated transistor Q3 or Q4 then begins to conduct. The current flowing from its collector to its emitter reduces the gate voltage of the associated Mosfet, effectively increasing its on-resistance, which then reduces the current. This protection is a fast-acting, cycle-by-cycle measure. At the same time, the voltages across the two 0.1W current-sense resistors are averaged by a pair of 10kW resistors and filtered by a 100nF capacitor. This averaged voltage is then applied to the non-inverting pin 5 input of op amp IC2, which amplifies the signal 28 times (27kW ÷ 1kW + 1). siliconchip.com.au The averaging effectively halves the sensed voltage, so this results in an overall amplification of 14 times, meaning that pin 7 of IC2b produces 1.4V per amp. This is measured by the AN3 analog input of IC1 (pin 3) and is converted to a digital value and processed by IC1. Should this voltage reach 4.9V or more, the drive to the transducer is switched off. 4.9V represents a 3.5A average current flow (4.9V ÷ 1.4V/A). This voltage can also be measured at the TP CURRENT test point. An overcurrent error is indicated as “OVR” on the LCD screen. When this happens, OVR will momentarily be displayed and the voltage reading will drop to reduce the current. With reduced current, the overload indication will cease as the voltage returns to its original setting. However, if the overload still exists, OVR will show again and the drop in voltage will be repeated. The OVR display will occur around once per second. To prevent this, the voltage/ power pot will need to be rotated anti-clockwise, and the frequency will then need to be adjusted to be closer to resonance. There is also a warning displayed if there is no voltage supply to transformer T1. This could be due to a blown fuse (F1). The display shows “FUSE NO V”, although there could be other reasons for the lack of voltage, such as an incorrectly wound transformer, a short circuit, or a supply break. Power limit control The current measured at the AN3 input is also used for controlling the maximum power applied to the ultrasonic transducer. The maximum power rating of the transducer is 50W, but this is not a continuous rating; the recommended continuous power is 43W. We limit power by reducing the voltage applied to T1 when the current reaches 3.3A. This equates to almost 40W (39.6W) when there is 12V applied to the transformer. The analog DAC output from pin 7 of IC1 is normally set to the same 1.23V as is at the pin 4 feedback input of REG2. With that voltage, the 22kW resistor from IC2a’s output has no effect on the regulator voltage as it has the same voltage at each end of the resistor, so no current flows. siliconchip.com.au Scope 1: the yellow trace shows the gate drives to Q1, while the cyan trace shows Q2, both being driven at 40kHz. Scope 2: the yellow trace shows the voltage applied to the ultrasonic transducer, while the cyan trace is the measured current scaled at 1.4V/A. However, if IC1 detects that the transducer current rises above 3.3A, IC1 increases the analog output from pin 7 of IC1, causing current to flow through the 22kW resistor, raising the voltage across the 5.1kW resistor. The regulator compensates for this extra voltage at the 5.1kW resistor by reducing its output voltage to maintain the 1.23V at its pin 4 feedback input. Frequency adjustment VR3 is used for fine frequency adjustment, while S1 and S2 move the span down or up, respectively. There are 16 spans labelled from Span 0 through to 9, then A to F. For the fine frequency adjustment, the voltage at VR3’s wiper is converted to a digital value in IC1 via its AN4 input pin. Since the voltage across the potentiometer is the same as the microcontroller’s supply voltage, this maps to the full ADC range. A 100nF capacitor from that pin to ground lowers the pin source impedance during the analog-to-digital conversion process. Australia's electronics magazine The internal oscillator for IC1 runs at 48MHz and can be adjusted in small steps using the OSCTUNE register. This can vary the internal oscillator frequency over about a 15% range in 128 steps. For Span 8, with a 40kHz centre frequency in driving the ultrasonic transducer, this allows a 5.2kHz control range in 37.5Hz steps. The cleaning timer also depends on the oscillator for accuracy. We compensate for any variance from the nominal 48MHz due to this fine frequency adjustment to maintain timer accuracy. The 37.5Hz step resolution in frequency change is sufficiently small to drive the ultrasonic transducer at its resonant point. However, the OSCTUNE register does not have sufficient range to ensure we can drive an ultrasonic transducer that is resonant outside the range of 37.291kHz to 42.506kHz that can be obtained by simply changing OSCTUNE. Thus, a coarser adjustment is used to widen the operating range. July 2026  33 Parts List – Adjustable Ultrasonic Cleaner 1 111 × 159mm double-sided plated-through PCB, 04105261 1 98 × 60mm double-sided plated-through PCB, 04105262 1 110 × 159mm front panel label 1 50W 40kHz ultrasonic transducer 1 compact 16×2 character alphanumeric LCD screen [Altronics Z7013] 1 M205 4A fuse (F1) 1 100μH 5A toroidal inductor (L1) [Altronics L6622, Jaycar LF1270] 1 ETD29 transformer assembly: 1 former, 2 N87 ferrite cores & 2 clips (T1) [Silicon Chip SC3888] Switches/potentiometers 3 tactile illuminated pushbutton momentary switches (blue, green or red LEDs) [Altronics S1174/5/7, Jaycar SP0612-4] 1 SPST 250V 6A rocker switch (S4) [Altronics S3210, Jaycar SK0984] 1 100kW linear 9mm vertical PCB-mount potentiometer with 6mm, 7mm-long spline shaft (VR1) [Altronics R1978] 2 10kW linear 9mm vertical PCB-mount potentiometer with 6mm, 17.4mm-long spline shaft (VR2, VR3) [Altronics R1946] 1 10kW miniature top-adjust trimpot, 3386F style or similar (VR4) 1 push-on D-shape knob for ¼-inch shafts [Altronics H6024, Jaycar HK7709] 2 18t spline 6mm knobs [Altronics H6109, Jaycar HK7733] Connectors 1 16-pin header, 2.54mm pitch (for LCD screen) 1 20-pin DIL IC socket 1 8-pin DIL IC socket 2 M205 PCB mount fuse clips 2 2-way 20A 5/5.08mm-pitch screw terminals (CON1, CON2) 1 3-way 20A 5/5.08mm-pitch screw terminal (CON3) 2 14-way IDC crimp connectors [Altronics P5314] 2 14-pin keyed box headers (CON4, CON5) [Altronics P5014] Hardware 1 171 × 121 × 55mm IP66 diecast aluminium enclosure [Jaycar HB5046] 1 2-4L (stainless) steel, aluminium round or square cross-section baking tray, 75mm tall or higher 1 65mm diameter DWV (drain, waste and vent) end cap [eg, Holman DWVF0194] 1 35mm-long 65mm DWV pipe or 65mm to 45mm pipe reducer [eg, Holman DWVF0382] 2 MG12 or PG7 cable glands (for the transducer cable) 1 mains Earth connector for attaching VR1’s shaft extension (6mm ID wire entry) [Altronics P2125A] 4 TO-220 insulating kits [Altronics H7210, Jaycar HP1140] 1 MG16 or PG11 cable gland (for the power supply cable) 1 200mm length of electrical insulation tape 4 100mm-long cable ties Screws etc 2 solder lug eyelets, M4 × 6mm screws, nuts and star washers (for transducer connection) 2 M3.5 × 6mm screws for mounting PCB to enclosure (in addition to the two supplied with the enclosure) 9 M3 × 12mm panhead machine screws 8 M3 × 6mm panhead machine screws 4 M3 × 12mm tapped spacers 34 Silicon Chip 2 M3 × 6.3mm tapped nylon spacers 4 3mm inner diameter nylon washers 7 M3 hex nuts 1 M3 × 25mm panhead machine screw + M3 × (15mm, 12mm, 6.3mm) tapped nylon spacers + 3mm ID nylon washer OR 1 35mm length of 6mm timber dowel (for VR1 shaft extension) Wire & cable 1 800mm length of 1mm diameter enamelled copper wire (for T1’s primary) 1 6.2m length of 0.5mm diameter enamelled copper wire (for T1’s secondary) 1 1m length of 7.5A sheathed figure-8 mains rated wire (for connecting the transducer) 1 400mm length of 10A hookup wire (for S4) 1 120mm length of 14-way 1.27mm pitch ribbon cable 1 50mm length of 5mm heatshrink tubing (for transducer terminals) Semiconductors 1 PIC16F1459-I/P microcontroller programmed with 0410526A, DIP-20 (IC1) 1 MCP6272E/P or LMC6482AIN dual rail-to-rail CMOS op amp, DIP-8 (IC2) 1 7805 5V 1A regulator, TO-220 (REG1) 1 LM2576T-ADJ 3A adjustable regulator, TO-220-5 (REG2) 2 IPP80N06S4L-07 or equivalent high-current N-channel Mosfets, TO-220 (Q1,Q2) [Silicon Chip SC6184] 2 BC547 NPN transistors, TO-92 (Q3,Q4) 1 1N4004 400V 1A diode (D1) 1 STPS1545F 45V 15A schottky diode (D2) [Altronics Z0065] 1 1N5404 400V 3A diode (D3) Capacitors 3 1000μF 25V low-ESR electrolytic 3 100μF 16V PC electrolytic 1 470nF MKT polyester 6 100nF MKT polyester 1 1.5nF MKT polyester Resistors (all ¼W, ±1% axial unless noted) 2 100kW 1 27kW 1 22kW 1 20kW 9 10kW 1 5.1kW 1 1kW 3 560W 1 68W 2 47W 2 100mW 1W SMD M6331/2512 resistors [ERJM1W, RS Cat 566989 or similar] Miscellaneous amounts of: Solder, JB Weld epoxy resin, neutral-cure silicone sealant and electrical tape Australia's electronics magazine siliconchip.com.au Fine-tuning is then done via OSCTUNE. The wider frequency range allows a variety of different transducers to be used, as the resonance range can be adjusted to suit. This coarser calibration is performed using the PR2 register within IC1. This sets the period and thus the frequency of the PWM drive waveform for the ultrasonic transducer. For our circuit, the PR2 adjustment provides steps of approximately 530Hz. We restrict this coarse adjustment to the range 33.683kHz to 46.859kHz. This caters to transducers that have a nominal 40kHz resonance. The value of the PR2 register is stored in flash memory, so it is recalled when power is applied. The PR2 value sets the Span setting (0-F) displayed on the LCD. The OSCTUNE value is effectively ‘stored’ in the position of VR3. There is the option to lock the Frequency setting and the Span so that they remain fixed at their last settings even when the power is switched off. Each setting can be independently locked or unlocked. When locked, the related control has no effect. Switches S1, S2 and S3 connect to the RA1, RA3 and RA0 inputs of IC1, respectively. The inputs are each held high (at 5V) by 10kW pull-up resistors. A closed switch is detected when it is pressed, as the input is pulled to 0V. Power supply 12-15V DC power for the circuit is fed in via CON1. The supply needs to be rated to deliver 4A or more. If using a 12V battery, it should have a capacity of 10Ah or more. More power can be produced with a higher voltage supply, such as a 13.8V 4A supply or a universal laptop power supply like Jaycar’s MP-3476. This supplies 12V at 6A or 14V/15V at 5A. Do not use a 16V or higher supply since the input capacitor for REG1 is only rated at 16V. If your supply has a power plug, remove it and strip the wires to connect to the screw connector at CON1. Power is switched by S4, which is wired back to the PCB via the CON2 screw terminal. LCD screen driving The LCD is driven in 4-bit mode, with the most-significant data bits D4-D7 of the LCD connected to IC1’s RB4-RB7 outputs. D0-D3, the least-­ significant data input bits of the LCD, are tied to ground. The enable and register select (EN and RS) also connect to IC1 pins RC2 and RA5. The contrast potentiometer (VR4) provides a voltage to the contrast input of the LCD and is adjusted for best display clarity. Display backlighting is via the BLA (backlight anode) connection to 5V and the BLK (backlight cathode) of the LED backlight connected to ground via a 68W current-limiting resistor. Switches S1-S3 are also lit while the unit is powered with their internal LEDs via 560W current-limiting resistors across the 5V supply. Next month The second half of this article next month will mainly cover the construction, setup and usage of the Adjustable Ultrasonic Cleaner. Assembling it is mostly straightforward, just requiring a bit of trickery so that all the controls (including those on the main and control boards) project through the front panel neatly. We’ll have all the details in the secSC ond part. For the enclosure (left), we have used a IP66-rated aluminium case measuring 171 × 121 × 55mm, this is the smallest size that will fit the Main Board. Next to it is the underside of the baking tray which we’ve fitted a 50W 40kHz ultrasonic transducer to, functioning as our ultrasonic bath. siliconchip.com.au Australia's electronics magazine July 2026  35