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USB--C USB Part 2 by Tim Blythman Power Monitor This compact device lets you monitor the voltage, current, power and energy supplied to a USB-C device. The first article last month covered some background information, the circuit details and reasons for the design choices. Now we’ll describe the construction and usage of this handy tool. T he USB-C Power Monitor can measure the Vbus voltage and current flowing between two devices; using this information, it can also calculate power and energy. That makes it similar to our USB Power Monitor (December 2012 issue; siliconchip.au/ Article/460) but with USB-C connectors, a more comprehensive display and extra capabilities. Since USB-C allows current to flow in either direction, the new Monitor must handle that, as well as USB-C’s higher voltage and current capabilities, up to 48V and 5A. It has an internal rechargeable battery to avoid loading the USB host. The Monitor also tests the state of the configuration channel (CC) lines, which are also new to USB-C. It has an OLED display module and three tactile switches for control. All these features are packed into a compact 80mm × 40mm enclosure. Construction The two PCBs are connected by soldered wire, ribbon cable or FFC (flat flexible cable) connections. That’s because pluggable connections have variable resistance and will interfere with the correct operation of the current shunt monitor. The smaller PCB has the USB-C plug and socket. We will build this first, since it is easy to test. The second PCB carries most of the parts and also forms the front panel of the completed unit. This PCB can operate by itself, without a battery, so the second PCB can also be tested for basic functionality before everything is joined. The case we have chosen requires three cutouts to be made. These are not too tricky, and they can also be tested for fit before the final assembly step. As you can see from our photos, the completed unit is compact and neat. Both PCBs are 0.8mm thick and feature surface-mounting parts, so you will need the usual SMT gear; a finetipped soldering iron (or medium/ chisel tip, if you prefer), solder, flux paste, tweezers, a magnifier and good lighting. Solder wicking braid will come in handy, too. Work outside or with good ventilation to avoid inhaling smoke from the flux. Connector PCB You might not need them, but Fig.4 shows the overlay diagrams for this PCB, which is coded 04102251 and measures 78 × 11mm (it’s 0.8mm thick). There aren’t many parts on it, but we think it’s the most tricky to solder because of the fully featured USB-C connectors and their fine pin pitch. We found socket CON2 to be most challenging, so we recommend starting with that. We haven’t tried it, but if you have a hot-air station and solder paste and are familiar with using them, then you might like to use them to assemble the connector PCB. This process would be closer to the reflow process used for commercial soldering of these parts. CON2 is much the same part that we used in the USB Cable Tester (November & December 2021; siliconchip. com.au/Series/374), although this time we are using a variant with shorter through-hole pins since the PCB is thinner. These pins are very fine and can easily bend if they are bumped; this could lead to short circuits with other pins, so be gentle. Place CON2 on the PCB and tack one of the larger shell pins, then confirm that the SMT pins on the top of the PCB are aligned and flat against the PCB. This should avoid the possibility Short-form Kit (SC7489, $60): this kit includes all the non-optional parts listed except the case, lithium-ion cell and glue. It will also include the FFC (flat flexible cable PCB) for joining the two PCBs. 78 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.4: there aren’t many components on this PCB; it does little more than pass all USB-C signals through and break out a few of them for connection to the main PCB. Soldering CON1 and CON2 will probably be the trickiest part of this project. of the part moving while you are trying to solder it. Clean the iron and add a small amount of fresh solder. Carefully add flux to the smaller pins and solder them. We’ve extended these pads where possible, as this will allow you to touch the iron to the pad and see that the solder has flowed and melted onto the pin. Flip the PCB over and solder the through-hole pins, including the four larger shell pins. If you think you have a bridge between pins, carefully use the braid and a little more flux paste to draw the excess solder away. The solder’s surface tension should hold enough solder behind to make a solid joint. If in doubt, add a little more, with some more flux to ensure it flows smoothly. The USB-C plug (CON1) is a straddle-­ mount part that clips over the edge of the PCB. This helps to lock it into place so it’s not likely to move during soldering. Its pins are also fine, and if they are bent at all, particularly sideways, then they may bridge to other pins. If it has a protective cap, leave it in place for now. Place the plug over the edge of the PCB and check that it is flat against the PCB and all the pins on both sides align with their pads. Carefully slide it sideways if needed. It should be parallel to the edge of the PCB, too. Add flux to all the pins and touch the iron to the end of each pad in turn until the solder flows onto the respective pin. The shell can also be soldered to the larger pads on the outside edge of the PCB; this will add mechanical strength. Check for solder bridges and use the braid with extra flux paste as needed. Once you are happy with it, fit the three resistors to this PCB. The larger part is the 15mW shunt; the other two are 220W. Clean up the excess flux on the PCB using the solvent of your choice. Some fluxes recommend specific chemicals, but we find that isopropyl alcohol is a good alternative. siliconchip.com.au Allow this PCB to dry and give it another inspection. If there is a short circuit between any pins, it will not work as designed. Remove the cap on CON1. At this stage, this PCB should be functional as a USB-C extension, so you can test it by connecting a fully featured USB-C cable (with plug) to CON2. Be sure to rotate the connector 180° to test both configurations. Ideally, our USB Cable Tester should be used for initial tests, since this will not cause or suffer any damage if there is a fault. The extended cable should give exactly the same results as the cable on its own, since all the lines are taken straight through. There may be a slightly higher cable resistance due to the extra cable junctions. Lacking that, connect a USB-C device you don’t care about too much to a computer through this extension and check that it works normally. We also used a USB-PD power supply connected to a USB-PD trigger device to test this PCB, since they are fairly cheap and will exercise the power and CC (configuration channel) wires. See the end of this article for an example of the boards we used for testing. If the tests work as expected, then test out the data wires using a computer or similar. Be sure to use it with a USB 3.x device so that you know that all the USB data circuits are functional. As before, the extended cable should give the same results as the cable on its own. If you run into any problems, go back and rectify them before using this PCB. Main PCB While the second PCB, coded 04102252 and measuring 80 × 40mm, has a few smaller parts, in comparison, it should be relatively straightforward (see Fig.5). Start with the smaller ICs and the regulator. IC3 is the AD8541 op amp (or similar) and should be labelled with the code A4A or A12, while IC4 is the MCP73831 charge controller and should be labelled KD, followed by a two-character lot code. They are both in SOT-23-5 (five lead) packages. Note that the pads for IC3 have been modified to allow either an SOT-23-5 or slightly smaller SC-70-5 part to be fitted since we will supply SC-70-5 parts in our kits. They are The main PCB (shown enlarged) has numerous SMDs, plus a through-hole LED that shines through a hole in the PCB solder mask. The OLED module is also mounted to be visible through a cutout in the PCB. A row of header pins can be fitted to CON5 if in-circuit programming of IC1 is required. Australia's electronics magazine September 2025  79 marginally smaller, so not too much more difficult to solder. If you’re sourcing the parts yourself and prefer to use an SOT-23-5 part, it should fit the same pads just fine (it’s a dual footprint). REG1, the MCP16252, is similarly small in a six-lead SOT-23-6 package and marked with the code MC and a two-character lot code. Be sure to check the orientation on this one, since it is symmetrical, unlike the fivelead parts. The alignment dot is below and to the left of the MC code; in other words, pin 1 is at lower left when the text is upright. Double-check its orientation before soldering more than one pin as it’s tricky to fix if you get it wrong! Follow with IC1 and IC2, the two SOIC parts; these should be a breeze after the smaller parts, but you still need to pay careful attention to their orientations. Diode D1 is quite small, but should be easy enough to manage. CON5, the third USB-C connector should be aligned flush with the edge of the PCB as much as possible. After the resistors, capacitors and sole inductor are fitted, this PCB will be fairly complete. There are only two different capacitor values; the five 10μF parts might be thicker than the five 100nF parts. They will be unmarked, though, so be sure not to mix them up. There are several different resistor values, so match the markings to the silkscreen or use a multimeter if you are unsure. On the PCB, the silkscreen values are generally below or to the right of the part when they are in a row, to avoid ambiguity. You can also check against the overlay diagram (Fig.5) and photos. You can also solder in the 3mm LED now. We’re using a through-hole part here, since two-lead SMD bicolour LEDs are not widely available. The K marking on the PCB corresponds to the cathode of the green LED in the package. Bend the leads as shown in the photos and solder it to the PCB. Keep the lead offcuts for later. Now is a good time to clean up the flux residue on the PCB, before the OLED and tactile pushbuttons are fitted; these parts will not appreciate being immersed in solvent. Allow it to dry and inspect the soldering for Fig.5: this PCB hosts most of the parts. Don’t mix up the various SOT-23/SC-70 parts (in 3-pin, 5-pin & 6-pin variants). Fortunately, there is a fair amount of space on the PCB, so the silkscreen markings should be easy to follow. Fig.6: the partially assembled main PCB – you can testfit the boards before they are turned into a single assembly. We recommend you take your time and ensure that they are a good fit individually before joining them together. 80 Silicon Chip Australia's electronics magazine any poor connections or bridges and rectify them if needed. Fig.6 shows the state of the PCB at this point. Finishing the main PCB You can now fit the OLED module and tactile switches to the main PCB. For the OLED module, desolder any header that has been attached to it and clean up the four pads. The easiest way to do this is to add solder to the pins so that they are all covered in a single, large blob of solder and then heat that while pulling the pins with pliers until they slide out of the board. After that, use a solder sucker to remove the excess solder bridging the pads. Now solder short wire offcuts to the four pads on the main PCB. These should point straight up and align with the holes in the OLED when it is overlaid. The best way to do this is to bend short pieces of wire into an ‘L’ shape and use the extended pad to secure them better. It’s a bit fiddly, but we think it leads to a very tidy result. Remove the OLED’s protective film and slot the OLED over the offcuts, then solder the OLED module to them. Be sure that the OLED is not too close to the edge of the PCB; otherwise, it could foul the enclosure. Another piece of wire can be soldered to the long pad near LED1 and bent over the OLED module. This will provide support to the other end of the OLED. Fit the pushbutton switches next. Their stems poke through the PCB to face outwards, so you may need to sit the PCB up using spacers or a PCB holder. Tack one lead and adjust the switches so that their stems are centred in the holes. This will look better and eliminate the chance of the switches binding. Once you are satisfied with the positions, solder the remaining leads. You can tidy up with a cotton-tipped swab or similar. Dip it in some solvent and wipe up any excess flux. Programming IC1 Chips purchased from the Silicon Chip Online Shop (including those in the kit) will be supplied in a programmed state, so will not need programming. You can skip to the next section if you have such a chip. To program IC1, you can fit a header to CON3. For our prototype, we just used a standard through-hole header strip and soldered it as though it were siliconchip.com.au The USB-C Power Monitor runs from an internal Li-ion rechargeable battery and can measure up to 60V and 5A. The loop in the FFC goes over the OLED module so that the cell will fit into the space above IC2 when the case is closed. With the cell stuck down using foam-cored tape, the main PCB should rest in place as a snug fit. This PCB becomes the lid and is attached using the screws included with the case. a surface-mounting part. It can stay in place since it will not foul the enclosure if installed squarely. You can see it in the photo of the completed assembly above. You can apply power to the PCB through CON5 (the USB-C power-­ only socket on the main PCB), if this is needed. Use a Snap, PICkit 4, PICkit 5 or PICkit Basic and choose the PIC16F18146 from the MPLAB IPE. Open the 0410225A.HEX file, use it to program the chip and confirm that the verification is successful. You should also see the OLED illuminate and display the main screen; the readings will be nonsensical, since there is no connection to the second PCB. Pressing S3 (>) should cause the screens to cycle. If this is the case, then all is well. If not, double-check your soldering before continuing. Enclosure It’s a good idea to prepare the case next, as that will allow the two PCBs to be checked before they are joined together. Note that the cutting here matches our prototype as built, with the USB-C socket (CON2) on the left and the plug (CON1) on the right. In other words, the CON5 USB-C power-­ only socket is on the same end as CON2. Because the assembled PCB with CON1 & CON2 is longer than the case, the final assembly step will involve passing CON2 fully through its hole (and out the side of the case) so the CON1 end of the PCB can be dropped into place. The PCB is then slid back so that the two connectors are in their final locations. siliconchip.com.au Because of the extra room needed for these manoeuvres, the holes will be slightly oversized. As such, the lower PCB will need to be secured with glue (but not just yet!). This will also provide reinforcement against wear and tear on the connectors. Fig.7 shows the cutting diagram, but you can also use the two PCBs to mark out the cuts as you go. For example, you can rest the main PCB on top of the case and mark the sides of CON5, rather than trying to measure out the dimensions with a ruler. The bottom of the holes for CON1 and CON2 should be level with the floor of the case, which is 2mm thick. Since the CON5 cutout is a notch at the top edge of the enclosure, you could use a sharp hobby knife or fine hacksaw to make the vertical cuts. Make a score mark at the base of the tab and carefully flex it with pliers until it snaps off. Then tidy the edges and make sure that the main PCB can sit flat on the top of the case. The other holes should be started with a drill at their outer edges. Make further drill holes along the length and use a file or knife to join those holes. Then enlarge the holes until the smaller PCB can be inserted and check that the lower PCB can slide freely and can be slotted into place from above. long, so wire, if used, should be the same length. This will neatly loop to one side of the case without bunching up. The loop provides space for the lithium cell. Pay careful attention to the orientation of the two boards in our photos. You can see that CON2 is at the same end as CON5 to match our cutting diagram and prototype. Start by soldering the FFC to the main PCB. We have aligned the striped conductor with the square pads on the PCB; this is pin 1. The FFC does not need to sit flat, but can pass at an angle just enough to clear the OLED module. Just like an SMT part, you can tack one lead and confirm that the FFC is square and aligned to the main PCB. You shouldn’t need to use flux since you will need to use a generous amount of solder. Tack the lead at Connecting the PCBs The two PCBs are ideally connected by a flat flexible cable (FFC), which is effectively a flexible PCB with the code 04102253. An alternative is to simply use light-gauge insulated wiring or ribbon cable. The FFC is 4cm Australia's electronics magazine Fig.7: the recommended cut-outs. You will need to swap the CON1 & CON2 cut-outs if you plan to fit the smaller board in the opposite orientation than we are recommending. September 2025  81 the other end and if everything looks correct, solder the remaining leads to their pads. Follow the same process to connect it to the second PCB. The FFC connects to the side opposite the resistors, so it can sit flat against the PCB. You can see the arrangement in the photo on page 81. Once this is done, take care with the assembly. The FFC is reasonably robust, but will not stand up to repeated flexing. It could tear if subjected to excessive force, or be kinked if it is bent too hard. Completion Now that the PCBs are connected, you could power up the unit (at CON5) and see that it is showing reasonable readings, close to 0V and 0A. Without a battery connected, our LED flashed red, then green and then switched off; if yours flashes green then red, the LED may be reversed, and it is best to correct that now. You can jump ahead to the setup and usage section if you’d like to run some further checks before gluing the PCBs down and closing everything up. Since the next step involves soldering the battery to the PCB, you should disconnect power. Take great care whilst working with the battery, since the lithium-ion cell will not take kindly to being short-circuited. Everything will be live (at up to 5V) from now on. Carefully prepare the leads for soldering. Our battery had a connector that we needed to cut off. Only cut one lead at a time to avoid shorting them with the cutters. Use tape to cover the ends so that only one is exposed at a time. Solder the leads to the terminals marked BAT1 on the PCB, observing the polarity seen in the photos and on the silkscreen. The Monitor should switch on. You can place it in a low-power sleep mode by pressing and holding S3 (>) until Screen 2 is seen. Then press S1 (down) to enter sleep; the text SLEEPING will appear before the screen blanks. Apply glue (neutral cure silicone) to the battery terminals on the PCB and cover any bare metal. This will add some extra strain relief and also insulate the bare ends of the wires. Now you can slot CON1 and CON2 into the case. Ideally, CON2 should protrude slightly from its end, with the lower PCB resting against that end wall of the enclosure. Add glue to secure the PCB in place and take care not to allow any to seep inside the connectors, especially the holes on the top of CON2. For now, apply just enough glue to make sure that the PCBs are mechanically secure. If needed, you can tidy up the external appearance by filling in the gaps in the case around CON1 and CON2 later. Now you should wait until the glue has fully cured to ensure that nothing breaks loose during the final stage. While waiting for the glue to cure, you can charge the battery via the CON5 USB-C socket. The LED should light up red and then change to green when charging is complete. Closing it up Use foam-cored double-sided tape to secure the battery to the inside of the case. It should sit against the lower wall, near the middle of the case. Resting it against the internal boss should ensure that it is clear of CON3 if fitted. LED1 is the other component that might conflict, but that should not be a problem if you use the same size cell we did. The main PCB is now placed on top of the case. Check that there aren’t any internal collisions with the battery. If all is well, secure the lid with the two screws included with the case hardware. They will sit slightly above the surface of the PCB. Don’t screw them down too firmly; the thin PCB is flexible and will be somewhat susceptible to cracking if stressed. Setup and usage Screens 1-4: there are four main operating screens and nine configuration screens. These operating screens are described in detail in the text. Screen 5: the brightness of the OLED screen can be adjusted here; the default value of 130 is near the midpoint of the adjustment range. Higher values will flatten the battery faster. Screen 6: the displayed energy units on the main page can be set to either Joules (J) or Watt-hours (Wh). This can be changed at any time without affecting readings. Screen 7: the TRIM factor on this screen sets the multiplier for voltage readings. Use a multimeter to compare the measured value against the displayed value. Screen 8: the current ranges are trimmed in similar fashion to Screen 7. For the high current range, apply and measure a load of at least 1A to ensure accuracy across the range. 82 Silicon Chip Australia's electronics magazine When the screen is blank, pressing any of the buttons should end the sleep mode. The unit returns to Screen 1 when this happens. A brief press of S3 (>) will cycle between the operating screens (Screens 1-4). A long press of S3 will enter the settings and configuration screens; there are nine of these, shown in Screens 5-13. You can exit the settings screens by another long press on S3. The main screen (Screen 1) shows the measured voltage, current and power as well as accumulated energy. Below the current is a timer that can run up to 99 hours. On this screen, the up and down buttons control the timer and energy counter. The state shown here has the timer stopped; the time display will alternate with ∧ START. Pressing ∧ will start the timer and the energy counter siliconchip.com.au will integrate the power value. You can always calculate an average power by dividing the energy by the time. Pressing ∨ will pause the timer (and energy counter) if it is running. Pressing it while paused will reset both values. The current display will show units of mA (to two decimal places) if the low current range is being used. The display will be in A (to three decimal places) when the higher range is in use. The arrow on the first line shows the direction of current flow (source to sink). Right to left corresponds to a positive value of power and energy. Since the power will always be the same sign as the current, this should be unambiguous. There is also a timeout that is only active on this screen. It is reset any time the Vbus voltage is above 1V, if the timer is running or any time a button is pressed. If the timer is counting down, it is displayed in small text (along with the low Vbus voltage) in the top left corner. The timer can be deactivated (as is the default), and we’ll discuss this in the configuration section. Sleep and battery The next screen allows the battery voltage to be checked by pressing the ∧ button. This actually measures the voltage supplied to the micro and adds an adjustment for the diode, REG1 and 10W resistor. So it will only be accurate when there is nothing powering CON5. This is on its own screen because it requires the boost regulator to be shut down and should not be done while the timer is running. It won’t cause any damage, but the readings will be inaccurate since the 4.096V reference will not be at specification. The reading should be treated like a typical Li-ion battery voltage; 4.2V is close to fully charged and 3.6V or lower is flat. Pressing the ∨ button on this screen will put the Monitor into low-power sleep mode. All timers and peripherals are shut down, as are REG1, MOD1, IC2 and IC3. If the timer from the main screen was running, it will be paused. The screen will show a SLEEPING message and then shut down. Pressing any of the buttons will wake it up. Any time the Monitor is not being used, it should be put into sleep mode to avoid flattening the battery. The time­out on the main screen has the same effect and will show the same SLEEPING message. siliconchip.com.au CC states The CC (configuration channel) lines are one of the new features that were introduced with USB-C. As we’ve noted in other articles, they have tripped up many engineers. So we thought that this screen (Screen 3) might help to shed some light on this feature. The Vbus voltage is also displayed at lower right. This screen depends on the connected devices complying with the standards, so if you see nonsensical readings, maybe there is a problem with whatever is connected to CON1 and CON2. It’s also possible that the 220W resistors in the Monitor are interfering with its operation, although they generally shouldn’t. The second line shows which of the two (CC1 and CC2) lines is used for CC signalling on the connected USB-C source; this corresponds to either the upper (A5) or lower (B5) connections on CON1 or CON2. This can help with troubleshooting cable orientation. A sink device must be connected to provide the pulldown on the CC lines before the source current can be read. If the text ∧ START is shown on the last line, the Monitor can provide that sink by pulling its internal 5.1kW resistors low. The ∧ button must be held down to apply the internal 5.1kW load and no other sink should be connected; this is the reason for the SOURCE ONLY warning. When a sink is provided, the second and third lines provide information about the source capabilities and status. You should see either → or ← pointing from source to sink, and some text describing the status. The direction is derived from the current through the 220W resistors. The status is derived from the voltage on the active CC line and the Vbus voltage. For example, a Vbus voltage over 5.5V is interpreted as a USB-PD voltage being negotiated; this is displayed with the text USB-PD. A LEGACY source is one that applies Vbus without a sink being connected. This implies a USB-A to USB-C cable or adaptor has been used on the source side. You might also see SOURCE LOW if the Monitor determines the source should be supplying 5V but is not. We have found that some devices don’t respond instantly to changes in the configuration channel. Some of the timeouts in the USB-C specification Australia's electronics magazine Screen 9: the low-current range works up to about 25mA, so a 220W resistor across 5V will provide an appropriate load for trimming on this page. Screen 10: the current offsets can be automatically trimmed by the page shown in Screen 4, but the value is shown here for completeness. Screen 11: you can also manually trim the current offsets by adjusting the parameter until the displayed current reads zero, as shown here. Screen 12: by default, the display timeout is disabled, but it can be switched on by adjusting the value upwards. The timeout only applies on the main screen if the Monitor is idle. Screen 13: the configuration is held in RAM, which will be lost if the battery runs flat. So we recommend you perform a SAVE after doing the initial calibration. allow over a second for some responses to occur, so this is to be expected. Offset trim Screen 4 shows a page used to trim the offset in the current-measuring channels. The offset changes with Vbus voltage, so it is best to have the expected voltage present when doing this. The default (zero) trim values are fairly accurate at 5V, since this is near the supply voltage of IC2 and IC3 involved in current measurement. When the ∨ button is pressed, the Monitor takes an average over 256 readings of the high and low current ranges. It then applies this as the offset to the raw ADC value, as shown at the bottom of the screen. As the text explains, the current September 2025  83 Left: this Adafruit 4396 USB-C socket breakout board is fitted with two 5.1kW resistors and a header. It will be handy during Monitor calibration and could also be useful if you need a 5V supply with a current readout. Right: a typical USB-PD trigger board has a USB-C socket, a USB-PD interface IC and an output connector. This example sets the requested PD voltage by solder jumpers; some can be controlled digitally, with an I2C serial interface or similar. should be zero for this to work correctly. If there is an idle or quiescent current that you wish to cancel out, this should be applied, and it can be trimmed out, too. An example of this is the load due to the Vbus sensing divider. Configuration Screens 5-13 are configuration screens. Most of these screens are fairly straightforward, and there are brief descriptions of each in the captions. The three TRIM screens adjust the multiplier used in calculating the Vbus voltage and high and low current ranges. The offset trim described above should be done before completing this step using the same Vbus voltage. You’ll need a multimeter or similar so that you can read a value to trim against. The parameter shown in the second line should be adjusted until the measured value (volts or amps) matches the displayed value. For the current ranges, you might see INVALID displayed if the Monitor thinks the analog voltage is near its limit or saturating; this is most likely on the low current range. The OFFSET pages are the same parameters as described in the Offset trim section, and there is little need to manually adjust these. They are simply provided for completeness. The Monitor will use the live settings at all times, although Screen 13 shows a page to save the settings to EEPROM. Since the Monitor has the battery permanently connected, there is little chance of the Monitor forgetting its settings in RAM. But if the battery were to run flat, it would do so. So we recommend you save the settings to EEPROM using the ∧ button once the Monitor is set up. If you ever have a problem with the settings being corrupted, the ∨ button will restore to active settings from the defaults in flash memory. You can then save these to EEPROM with the ∧ button to complete the RESTORE. Accessories During testing, we used various cables, adaptors and breakout boards to test and probe the operation of the Monitor. You’ll need a standard USB-C plug-plug cable to use the Monitor, just as you would need such a cable to operate the device you are testing. A small breakout board like Adafruit’s 4396 USB Type C Socket Features & Specifications ● Main screen reports current, voltage, power, energy (in J or Wh) & time ● Configuration channel (CC) status screen ● All 24 USB data lines pass through ● Self-contained with 400mAh rechargeable lithium battery ● Internal battery means no extra load on the USB circuit under test ● Compact case is only 80 × 40mm ● Automatic offset trimming ● Voltage measurements: up to 60V with 10mV resolution ● Current measurements: up to ±5A with 1mA resolution; 10μA resolution below ~25mA ● Power: up to 300W with 1mW resolution (limited by V and I) ● Energy: up to 999999J (1mJ resolution) or up to 999Wh (10μWh resolution) ● Battery consumption: <20mA, giving 20 hours of usage per charge ● Sleep mode: <10μA drawn from battery, less than typical self-discharge 84 Silicon Chip Australia's electronics magazine breakout (shown in the left-hand photo) could be handy for calibration. Any similar breakout board that exposes Vbus, GND and the CC lines of a USB-C socket should also work. We wired up the two CC lines to allow the breakout to behave as a sink; there is a 5.1kW resistor from pin A5 to ground and another 5.1kW resistor from B5 to ground. A three-way header socket with the middle pin removed has the right pitch to connect to ground and Vbus. The photos at upper left show this gadget from both sides. This can be used for calibration, as we mentioned earlier, or to turn the Monitor into a current and voltage display for a simple 5V power supply. If you need access to higher voltages, a USB-PD trigger board (as seen in the photo above) might be an alternative. Conclusion The USB-C Power Monitor is a necessarily more complex design than its predecessor from 2012. It allows monitoring of the higher currents and voltages that USB-C allows. It can also provide information about newer features specific to USB-C. After it is set up, operation is straightforward. Typically, you would connect your device to its host or power supply using a standard USB-C plug-plug cable. The Monitor is fitted inline with the device to be checked. USB-C’s reversible plug and socket mean that you have some flexibility in how it is connected. Once you have adjusted the trim offsets to your liking, you can monitor the current, voltage & power. Starting the timer will allow you to check total energy consumption over a period and thus also average power consumption. The CC Connection State page (Screen 3) allows you to check the behaviour of USB-C’s configuration channel. Make sure to put the unit into low-power sleep when you are finished so that the battery does not SC run flat. siliconchip.com.au