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Our SMD Test Tweezers project from the October 2021 issue has been extremely popular. This did not come as a surprise given that they are handy, compact, easy to use, easy to build and the kit cost is reasonable. We decided to see what features we could add simply by upgrading the microcontroller at its heart. Improved Test SMD Tweezers T he SMD Tweezers are a simple but clever design. A PIC12F1572 eightpin microcontroller powered from a button cell is used to probe resistors, diodes and capacitors and then display its findings on a tiny OLED screen. The PIC12F1572 does a respectable job, but the Tweezers software takes up all but 42 bits of the available flash memory, leaving no room for expansion. We used the PIC12F1572 for the original SMD Test Tweezers as it was the cheapest available at the time, apart from its close relative with less memory, the PIC12F1571. Until recently, the PIC12F675 and later PIC12F617 were our 8-pin micros of choice, but Microchip keeps bringing out new parts with better performance and more features at lower prices, so we try to keep up. The PIC12F1572 is more capable than the older PIC12F675, as we explained in our feature at the time (November 2020; siliconchip.com. au/Article/14648). We also used the PIC12F1572 for our Christmas Ornaments in the same issue (siliconchip. com.au/Article/14636). However, when we looked into upgrading the Test Tweezers with some software improvements, we realised that the PIC12F1572 did not have enough free memory to add new features or improve existing ones. For that, we would have to move to the latest PIC generation. So when a new family of PICs became available, we began to investigate what we could add by using them. For more background on what these parts offer and what we learned in programming them, see the accompanying feature article on the new PICs that starts on page 80. A new PIC The original SMD Tweezers don’t use any exotic peripherals within the micro; the analog-to-digital converter (ADC) and watchdog timer that the software requires are found in most PIC microcontrollers. The low power sleep mode is quite standard too, and is essential for standby operation when powered from a cell. This allows the Tweezers to be left idle but ready to work at a second’s notice. The I2C interface to the OLED display is emulated in software by toggling GPIO (general purpose input/ output) pins, a technique often known as “bitbanging”. This all means that just about any 8-pin microcontroller with more program memory could be used for the SMD Tweezers. In mid-to-late-2021, after developing the original Tweezers, we became aware of the PIC16F152xx series of microcontrollers. The range spans parts from eight to 40 pins. While the range has features that are modest by current standards, they are still more capable than older parts like the PIC12F675. The PIC16F15213 and PIC16F15214 are the 8-pin parts in the range, and they are cheaper than the PIC12F1572, although the current part shortages mean that availability is poor. Importantly, the PIC16F15214 is available in the SOIC package and has twice the flash memory of the PIC12F1572. As we mentioned in our feature from November 2020, Microchip does a pretty good job of maintaining pin compatibility between parts, and the PIC16F152xx series is no exception. The upshot is that the PIC16F15214 is both cheaper and fully capable of replacing the PIC12F1572 as the controller for the SMD Tweezers, while also having the larger program space needed for us to add new features. Tweezers 2.0 We have implemented three major updates to the Tweezers. Firstly, we expanded the capacitance measurement range in both directions (it can measure both larger and smaller capacitances than before). Secondly, we added a calibration and setup procedure. Finally, we improved usability for left-handed people (or those who want to hold something like a soldering iron in their right hand) by allowing the screen display to be rotated by 180°. These improvements have all been made in software, so apart from changing the PIC12F1572 to the By Tim Blythman 72 Silicon Chip Australia's electronics magazine siliconchip.com.au Features & Specifications ∎ Uses identical hardware to the original Tweezers (October 2021; siliconchip.com.au/Article/15057) apart from the PIC microcontroller ∎ Identifies component type (resistor, capacitor, diode or LED) and measures critical values ∎ Resistors: value from 10W to 1MW ∎ Diodes: forward voltage up to about 3V ∎ Capacitors: value from (approximately) 10pF to 150μF ∎ Cell voltage with nothing connected ∎ Low power sleep when idle avoids the need for an on/off switch ∎ Instant wake-up by touching probe tips together ∎ Option to select left-handed or right-handed display ∎ Calibration of internal and contact resistance PIC16F15214, the hardware is identical and the general operation is much the same. Circuit details Fig.1 shows the circuit, which is the same as last time, besides IC1. All the readings are displayed on a tiny OLED module connected to CON2. IC1 drives its RA5 (pin 2, IOTOP) and RA4 (pin 3, IOBOT) pins high and low and measures the voltage present on pin 5 with its ADC peripheral. For example, it can determine the resistance of a resistor connected between the CON+ and CON− points using the voltage divider equation. Diodes will present their forward and reverse voltages between CON+ and CON− when the micro applies a voltage. The micro determines the diode’s orientation, showing its polarity and forward voltage. Capacitors are first charged by bringing IOTOP high and IOBOT low and then characterised by measuring the rate of discharge when IOTOP is brought low. The Tweezers can even measure their own supply voltage by reading the voltage of its internal 1.024V reference relative to that supply voltage. These features are already present in the original Tweezers, so we suggest you refer to the original Tweezers article (October 2021) for more detail on how these original features work and how the values are calculated. In theory, this expands the range by a factor of 256, but in practice, using this entire range is not possible. The upper limit is around 150μF now, equivalent to about 12 bits or a factor of 16 higher. The first reason for this is that higher values would overflow the 32-bit mathematical calculations that are required. The second is that the time needed to charge and discharge a larger capacitor becomes unreasonably long, in the order of several seconds between readings. The only way to overcome this would be to change the series test resistor, which would affect the other readings too. The relatively high value of the series test resistor also means that capacitance readings can be distorted by leakage current. Since leakage is typically higher in higher-value parts, especially in electrolytic capacitors, the accuracy and usefulness of these higher ranges are less than what seems theoretically possible. So higher value capacitors can be measured and will return a reading, possibly after a brief delay, but the accuracy will not be as good as for lower values. Low capacitance measurements Values lower than 1nF are measured in an entirely different fashion. This method is so sensitive that it can measure the capacitance of the touch of a hand, in the order of picofarads. It’s called shared capacitance sensing, and we used it to detect finger touches in the ATtiny816 Breakout Board of January 2019 (siliconchip. com.au/Article/11372). It works by comparing the relative magnitude of two capacitors by initially charging one and discharging the other, as shown in Fig.2. When they Improvements The upper limit of the capacitance range was limited by the use of an 8-bit counter to time the discharge. With more flash memory and RAM available, we can instead use a 16-bit counter. siliconchip.com.au Fig.1: the circuit for the updated Tweezers is practically the same as the old version, except IC1 is now a PIC16F15214. It can perform all its tests by applying different voltages to the IOTOP and IOBOT pins and testing the voltage on the IOTEST pin. Australia's electronics magazine April 2022  73 A few constructors had difficulty finding the brass strips we recommended for the original Tweezers. Standard header pins are a substitute and are easily aligned for soldering while in their plastic shrouds. There are even gold-plated versions available. We used a low-profile header socket (Altronics P5398) so that we could remove the OLED module during prototyping, to allow access to the programming pins. This also required us to cut down the header pins on the underside of the OLED and remove the plastic spacer block. The alternative is to simply solder the OLED directly to the main PCB. are connected, the charge present is shared between the two in proportion to their capacitances. The ratio of the initial and final voltages relates directly to the ratio of the capacitances. The theory and mathematics are explained further in the ATtiny816 Breakout Board article. In the case of our new Tweezers, a capacitor connected to CON+ and CON− is charged up via the 10kW resistor. The second capacitor is actually the tiny internal capacitor that is used to sample and hold the voltages read by the microcontroller’s ADC. This capacitor is nominally 5pF, and it is discharged by sampling an ADC channel connected to ground. Fortunately, the ADC peripheral has a selection to make an internal ground connection, so this does not require an extra pin. The external capacitor is disconnected from its resistor, and the two capacitors are connected by taking an ADC reading from the external capacitor. An equation similar to the voltage divider equation is used on the ADC result to calculate the value of the external capacitor. The way the capacitors share the charge is analogous to how resistors share voltage in a divider chain. The software also makes minor adjustments to account for some of the stray capacitance that is present and significant at these magnitudes. We made some tests on real capacitors in the picofarad range to fine-tune these readings. The lower limit is fairly arbitrary and is chosen to avoid the Tweezers detecting stray capacitance as a component to be measured, which could cause them not to power down correctly. At these scales, even the way the Tweezers are held can change the reading substantially. As the ADC reading nears its upper limit for larger capacitances, the resolution is poor around 1nF, and steps grow to be as far as 100pF apart. So the Fig.2: Cx is the device under test (DUT) connected to the Tweezer probes, while C1 is the ADC sample-and-hold capacitor inside the microcontroller. The capacitors are connected by sampling Cx with the ADC. If the value of Cx equals C1, the resulting voltage is half the initial voltage. It’s analogous to a resistive voltage divider, and the formulas are much the same, with the capacitor charge replacing the voltage across the resistors. 74 Silicon Chip Australia's electronics magazine readings using this method are always shown as pF, and other methods are used for measurements in nF or μF. We’ll detail the calibration and setup process after construction is complete. Construction The assembly procedure is identical to the October 2021 design, but we’ll go over it again for those who haven’t seen that article. The SMD Test Tweezers are built using three PCBs, with the main one coded 04106211 and measuring 28 x 26mm. Refer to the PCB overlay diagrams, Figs.3 & 4, during construction. The main PCB is not hard to build, even if the parts are all surface-mounting types. Gather your SMD tools and supplies. We recommend a fine-tipped soldering iron, a magnifier, some flux paste, solder wicking braid and tweezers, at a minimum. The small PCB needs something to hold it in place. If you don’t have an appropriate vice tool, you can use an adhesive putty like Blu-Tack instead. If possible, set up some fume extraction to deal with the extra smoke that comes from working with flux, or work near an open window or outside. A tip cleaning sponge is handy too. Apply flux to the top PCB pads for IC1 and the three passive components, then rest IC1 in place using tweezers, ensuring the pin 1 dot or bevel is towards the curved end of the board. Align the part within the pads, clean the iron’s tip, apply fresh solder and tack one lead in place. Adjust the IC if necessary to ensure it is flat against the PCB and aligned to the pads. Then solder the remaining siliconchip.com.au Fig.3: construction of the Tweezers is the same as last time (October 2021) except that IC1 is a different, pin-compatible microcontroller with more memory. There aren’t many components to fit but make sure that IC1 is orientated correctly. pins, cleaning your iron’s tip and adding solder as necessary. Use the braid to remove any solder bridges by adding more flux, then pressing the braid against the excess solder with the iron. Carefully drag both iron and braid away when the solder has been absorbed. The remaining three components are not polarised, so their orientations are unimportant. The capacitor sits near CON−, while the two identical resistors flank IC1 at its other end and side. Use a similar technique to IC1. Tack one lead, adjust the part, then tack the other lead. You can also go back and refresh any leads if the joint doesn’t look right. It should be smooth and glossy; you can add more flux at any stage to help improve solderability. Then solder the single component to the back of the PCB. Centre the cell holder to align the two external pins to their pads. If your iron is adjustable, turn it up while soldering this larger part. You should also ensure that the wider opening on the cell holder faces the rounded edge of the PCB to allow access for the cell to be fitted and removed. As before, apply flux, tack one lead in place and adjust the position. Then solder the other lead. For these much larger pads, it can help to apply extra solder directly to the pad to create a robust fillet, which you can see in our photos. With the surface mounted parts fitted, you can clean up the PCB using the flux cleaner designated by the flux’s data sheet. Methylated spirits or isopropyl alcohol are good all-round alternatives for cleaning many fluxes siliconchip.com.au too, while general-purpose flux cleaners are also available (and generally work better than plain alcohol). Just ensure that any flammable solvent has fully evaporated before moving on to the next steps. need a fairly new programmer and a new version of Microchip’s MPLAB X IPE (integrated programming environment). It can be downloaded as part of the MPLAB X IDE from siliconchip. com.au/link/abd2 We’ve tested with versions v5.40 Programming IC1 and later. You may also need to downUnless you’ve bought a pre-­ load a DFP (device family pack); this programmed PIC, IC1 will need to be can be downloaded from within the programmed with the firmware for this IDE, and the IPE then detects that the project. You can jump over this step DFP is installed. You should look for if your microcontroller has been pro- the PIC16F152xx family. grammed already. You will also need a recent proAs we noted in the panel, the grammer such as a Snap or PICkit 4 PIC16F15214 is a much newer part as the older PICkit 3 is not supported than the PIC12F1572, so you will for these parts. Parts List – Improved SMD Test Tweezers 1 double-sided PCB coded 04106211, 28 x 26mm (main PCB) 2 double-sided PCBs coded 04106212, 100 x 8mm (Tweezer arms) 1 PIC16F15214-I/SN or PIC16F15214-E/SN 8-bit microcontroller programmed with 0410621B.HEX, SOIC-8 (IC1) ● 1 0.49-inch 64x32 OLED module (Silicon Chip Online Shop Cat SC5602) 1 surface-mount coin cell holder (BAT1) [Digi-key BAT-HLD-001-ND, Mouser 712-BAT-HLD-001 or similar] 1 CR2032 or CR2025 lithium coin cell 1 5-pin right-angle male pin header (CON1; optional, for programming IC1 in-circuit) 1 100nF SMD 50V X7R ceramic capacitor, 3216/M1206 size [Altronics R9935] 2 10kW 1% SMD resistors, 3216/M1206 size [Altronics R8188] 2 15 x 2mm short pieces of thin (eg, 1mm) brass sheet for tips (optional) OR 2 gold-plated header pins for tips (see text) ● 1 40mm length of 30mm diameter clear heatshrink tubing (optional) 2 100mm lengths of 10mm diameter heatshrink tubing (optional) 1 4-way low-profile female header strip (optional, for CON2; can be cut from Altronics P5398) ● ● these parts have been changed compared to the original Tweezers A complete kit (SC5934) is available at siliconchip.com.au/Shop/20/5934 Australia's electronics magazine April 2022  75 Fig.4: the PCB for the Tweezer Arm section. Connect the programmer to the PCB at CON1, aligning the arrows that mark pin 1. You could solder on a header, but we find that holding a short header strip in place and pressing it firmly against the pads to make contact is usually sufficient. Select the PIC16F15214 part and open the 0410621B.HEX file. You may need to change the settings to allow the programmer to apply power. Then click “Program” and check that the part programs and verifies correctly. Tweezer arms The two arm PCBs should be attached next, as the OLED module covers much of the main PCB, limiting access. Our first version of the Tweezers used small pieces of brass strip to give the arms finer tips than just the bare PCBs would provide. If you can’t find a brass strip, then we suggest an alternative that will provide your Tweezers with gold-plated tips! Many header pins are gold-plated and are a good size for working with small components. These can be used instead of the brass strip, but unlike the brass strip, we found it easier to solder these to the arms after attaching the arms to the main PCB. The other advantage of using the header pins is that they are a good fit for breadboards and jumper wires, making it very easy to connect the Tweezers to other components for hands-free readings. The updated kits will include gold-plated headers for this purpose. We recommend fitting the arms roughly in line with the edges of the PCB but slightly tilted inwards with It helps to apply extra solder directly to the pad of the Tweezer arms to make a robust fillet. 76 Silicon Chip around 15mm separation at the tip ends. Like the SMD parts, roughly tack the arms in place and adjust them to your liking. We prefer fitting the arms with the writing and main contact trace running down the inside. This helps shield and isolate the trace from outside contact or stray capacitance. Test the action and pressure of the Tweezers when the arms are positioned, then when you are happy, apply a generous amount of solder on both sides of the main PCB to secure them firmly in place. To fit the tips, find a strip of about six pin headers (to maintain the 15mm separation) and while the pins are still in the plastic holder, solder the tips of the arms to the short ends of the headers. Using the holder will keep the pins parallel and even. Again, apply a generous amount of solder when you are happy with the tips, then carefully and evenly pull the arms and their tips out of the plastic holder. We find that some pointynosed pliers are handy to help in this situation. OLED screen The final step is to fit the OLED display module. You can solder the module directly to the main PCB. But since we had to do a lot more testing for this new version, we used a low profile header socket to allow the OLED to be removed. This is necessary because the programming pins are also used to interface with the OLED screen. We used the PIC Programming Helper from June 2021 (siliconchip. com.au/Article/14889) to help with our testing. But we also needed to do some testing and tweaking on the final design, so having a removable display was handy for these later stages. We used a low-profile (5mm high) header socket to keep the unit compact, and it’s what you can see in our photos. But we recommend using the direct mounting method unless you are considering designing your own firmware. So we’ll describe that. If the OLED module’s header is not attached, solder it now, at right angles to the module’s PCB. Then mount the module onto the PCB. You might find that the back of the OLED module touches IC1. In this case, use BluTack or a cardboard shim to keep the two apart until the module is securely soldered. That should leave the long pins protruding at the back of the PCB. You can trim them carefully with a sharp pair of sidecutters. Testing Fit a CR2025 or CR2032 3V coin cell into the cell holder, noting the polarity on the cell holder. After about a second, the OLED should show R HAND as per Screen 1. If not, check your soldering and that 3V is present on either the OLED module’s header pins or pins 2 and 3 of CON1. If 3V is not present, the cell may be flat or there is a short circuit. Remember to check the reverse of the PCB, as the cell holder, arms and OLED header are all very close together. Before you proceed to use the SMD Test Tweezers, you might like to go through the calibration procedure as detailed in the panel overleaf. Operation With the calibration and setup The tips might look a bit wonky, but when the arms are squeezed to bring them together they become parallel at about the distance you would typically use them (wide enough to hold a typical SMD component). Australia's electronics magazine siliconchip.com.au complete, normal operation will start. You should see a display indicating the battery voltage preceded by the letter B. After five seconds, the Tweezers will enter sleep mode and can be woken by touching the tips together. At this point, the new Tweezers work much the same as the older version, apart from the expanded capacitance range. If you close the tips to measure the short circuit resistance, you should see a value jumping around between 0W and 1W if everything is working correctly. We measured the current consumption on our prototype as much the same as the original Tweezers. The new Tweezers use around 4mA when working and 5μA when sleeping. So the cell life will depend mainly on how much they are used, tending towards the shelf life of the cell. Finishing touches Like we did with the original Tweezers, you might also consider adding some heatshrink to the Tweezers to add some protection and to keep the battery from being removed. The 10mm heatshrink can be put over the arms, leaving just the tips exposed. It should be pushed up firmly against the main PCB before being shrunk with a heat gun. The wider heatshrink fits over the main PCB and should overhang the end enough to prevent the cell from being removed. Of course, you will have to remove and replace the heatshrink to replace the cell. Screen 1: the first display when the Tweezers are powered on is the HAND setting, orientated in correspondence to the setting. Leaving the tips open selects right-handed operation. Also, be careful to not shrink the large heatshrink too tightly around the OLED, as its glass screen can be fragile. Aim heat along the edges to avoid heating the OLED and battery, and only shrink enough to secure everything in place. Kit availability & upgrading As the hardware is the same as before, we will update our SMD Test Tweezers kit to include the new micro programmed with the latest software. The kit still includes the heatshrink tubing mentioned above, along with everything else you need to build the tweezers. We’ve also added two goldplated pin headers for the tips. While we think the kit cost is low enough that it’s worthwhile simply building new Tweezers, if you really want to upgrade a pair you’ve already built, you can order the programmed micro from us and swap it over. We suggest you only do this if you are confident in removing SMDs and cleaning up the board to accept a new chip. This is most easily done with a hot air station, although it can be done with a regular soldering iron if you know how. Future improvements The SMD Tweezers are somewhat limited by only having one resistor to apply voltages to components, which is in turn limited by the 8-pin PIC. The 10kW resistor limits the applied current to about 300μA, meaning that the diode forward voltages reported are much lower than expected, and LEDs do not light very brightly. We are considering a more complicated SMD Tweezers design using a chip with, say, 14 pins. That might let us add new test modes and improve the existing ones. The extra pins mean we could have multiple current-­limiting resistors and thus a choice of test current. As well as expanding the range, additional test resistors will also improve the overall accuracy. Caution Like any project that uses coin cells, the Tweezers should be kept well away from children who may ingest them. The Tweezers also have quite pointy tips, another reason to keep them out of reach of curious fingers. Improved SMD Test Tweezers Complete Kit for $35 Includes everything pictured (now comes with tips!), except the lithium button cell. ● ● ● ● ● ● Resistance measurement: 10W to 1MW Capacitance measurements: ~10pF to 150μF Diode measurements: polarity & forward voltage, up to about 3V Compact OLED display readout with variable orientation Runs from a single lithium coin cell, ~five years of standby life Can measure components in-circuit under some circumstances siliconchip.com.au SC5934: $35 + postage siliconchip.com.au/Shop/20/5934 Australia's electronics magazine April 2022  77 Setup and calibration The accuracy of modern surface-­ mounted resistors is excellent and, as built, the SMD Tweezers will distinguish resistors well enough for most constructors. Still, the extra program space available on the PIC16F15214 gives us room to add some routines to add some settings and calibration constants. With all of us at Silicon Chip being right-handed, we now realise an overlooked aspect that probably makes the original Tweezers very difficult to use for the left-handed. So the first new setting is the option to flip the display so that it is legible when the Tweezers are held in a left hand. There is also the option to set the value of the nominally 10kW series resistor between pins 2 and 5 of IC1. Rather than trying to measure its value, we recommend testing an external part of a known value and adjusting the calibration until the Tweezers measure it correctly. The series value is simply adjusted in proportion to the desired change in calculated resistance. For example, if your displayed test resistor is 1% low, increase the series resistor value by 1%. This won’t adjust for things like trace and contact resistance, so there is a separate calibration step for those. Still, the preset value we have loaded into the Tweezers firmware will be quite accurate, as long as your Tweezers build is similar to ours. You may have noticed that the Tweezers do not have any buttons. So the various settings are configured using the only input device available: the probe tips! We can step through the setup and calibration by opening and closing the tips of the Tweezers at various points. It’s a slow but effective process, made easier by having a screen to show what is happening. Look at the flowchart shown in Fig.5 as we explain the process. The setup procedure only runs when the microcontroller is powered up, so it can be triggered by removing and reinserting the cell. The right-hand or left-hand operation setting is selected at the instant power is applied. If the tips are open, right-handed operation is selected; otherwise, left-handed operation is set. A message is also shown to RELEASE (Screen 2) the tips, and the microcontroller waits for this to happen so that later calibration steps are not triggered inadvertently. If you find it fiddly to insert the cell while holding the tips closed, join the tips with a female-female jumper wire while inserting the cell. The handedness setting is kept in RAM, saving on wear to flash memory. Since it is set every time power is applied, there is no need for non-volatile storage. As the remaining calibration steps can be a bit fiddly, there is the option to skip them. You enter calibration by holding the tips together when prompted (Screen 3) or leaving them open to skip. If the tips are left open for about the first 10 seconds after powerup, the settings are the same as the original Tweezers. The next step is to adjust the value of the nominally 10kW series test resistor. The OLED displays CAL R+ and a countdown timer (Screen 4). Any time the tips are closed during this phase, the displayed value will increase, and the timer will reset. This is followed by the CAL R- phase (Screen 5), which works much the same but allows the value to decrease. If any changes are made, the cycle repeats the CAL R+ and CAL R- steps until no more changes are made. The OLED then prompts to save the value; again, touching the tips together before the displayed timeout is confirmation that the value is to be saved Screen 2: at various times during setup, you may be prompted to RELEASE the Tweezers by opening the tips to ensure that multiple settings are not inadvertently made. Screen 3: the first prompt is to complete the calibration process and is accompanied by a nominal five-second timer. If the tips are left open during this time, calibration is skipped. Screen 4: when the tips are closed on this screen, it will increase the saved value of the series test resistor in 1W steps. See Fig.5 for a flowchart explaining the process. Screen 7: this screen shows while the value is saved to confirm that your selection has been acknowledged. Screen 8: you are prompted to close the tips to calibrate their contact resistance. If you don’t, the saved value is not changed. Screen 9: the contact resistance is measured around 20 times to get an average. The value shown here is higher than the default value of 16W. 78 Silicon Chip Australia's electronics magazine siliconchip.com.au ► and, if this is done, a brief message is shown indicating this. These are seen in Screen 6 and Screen 7. Finally, whether any changes are made or saved, the value of the series test resistor is freshly loaded from flash memory and displayed for user confirmation. The next step to set the contact resistance is simpler, as this is measured rather than entered. Note that the timers shown on these screens are not high-precision. The internal timings vary depending on what is displayed (especially changing numbers, which take time to render). We’ve tried to make the countdown timers appear reasonably consistent as seconds, but they are not highly accurate. The prompt seen in Screen 8 is the start of the contact resistance calibration. When the tips are held together, Screen 9 is seen. This shows the measured contact resistance, averaged over several readings. The default value is 16W, as measured on our prototype. If the tips are accidentally opened, the process aborts, and you will need to restart the calibration process to repeat it. Otherwise, the averaged value is shown along with a prompt to save it, as seen in Screen 10. Close the tips to Fig.5: a flowchart representing the setup and calibration process that occurs when power is first applied to the Tweezers. It looks complicated, but it is simple to go through once you understand the concepts, and the Tweezers prompt you with what to do at each step. confirm or leave them open to allow the counter to time out. Screen 11 shows the actual value loaded from SC flash memory. Screen 5: similarly, this screen allows the series test resistor value to be decreased. If any change occurs, these two steps are repeated until no change is detected. Screen 6: this prompts you to confirm that you wish to save the entered value to non-volatile flash memory. Close the tips to do so. Screen 10: if you don’t get this message, the Tweezers have detected that the tips may have been opened, so the measured value is inaccurate. Screen 11: finally, the actual value saved in flash memory is reloaded so that you can confirm that the saved value is correct. siliconchip.com.au Australia's electronics magazine April 2022  79