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Cable U S B Tester Our USB Cable Tester, introduced last month, is ideal for going through piles of cables and sorting them out. It's also a great first step in diagnosing a faulty USB-connected device. It can perform continuity and short-circuit checks on practically any USB cable and will report problems such as high resistance in the power wires; a source of frustrating intermittent faults. Part 2: by Tim Blythman I n the initial article last month, we described the reasoning and principles of operation behind the USB Cable Tester. Bristling with all the standard USB sockets, it will test and diagnose any cable with either a USB-C or USB-A (2.0 or 3.2) on one end and any of USB-C or USB-B (such as 2.0, 3.2, micro or mini) on the other end. It will report whether the cable is suitable for power only, USB 2.0 or USB 3.2 operation (and indicate whether one or two SuperSpeed lanes are present). With USB 3.2 (which has replaced USB 3.0 and USB 3.1), each SuperSpeed lane consists of four wires, forming differential pairs in both (upstream and downstream) directions. The unit scans every combination of wires among the upstream facing siliconchip.com.au and downstream facing ports. It can tell you which wires are internally shorted or open circuit to help with diagnosis and repair. The USB Cable Tester also runs pulses of up to 1A through the cable's power (VBUS and GND) wires to assess their ability to carry current under realworld conditions. The resistance and voltage drop is reported. This feature will ferret out many cables that are causing intermittent problems. When devices like portable hard drives mysteriously stop working, it's possibly due to their high current needs being hampered by poor connections. With this tool, you can weed out dodgy cables and choose the best ones for high-current applications. Now you can know for sure if it's the cable Australia’s electronics magazine or the device that's causing problems. The USB Cable Tester can also run tests when only one end of a cable is plugged in, and it does this for three reasons. Firstly, it verifies cables that are OTG (USB on-the-go) compatible, which short their GND and ID pins. This state indicates to a device that it should instead behave as a host. Since OTG cables are usually adaptors, their other end is typically a socket, so you can't plug in it at both ends. The second reason is to help those who construct and repair cables. You can use it to check individual cable halves, mainly to ensure that there are no shorts between any conductors. The third is perhaps the most important. That is to check that the very fiddly USB sockets have been December 2021  85 correctly soldered to the PCB. It's a kind of self-diagnosis, if you will. We will offer a different order of construction than usual to take advantage of this self-diagnosis feature. PCB layout The internal photos and the overlay diagram (Fig.3) show that the USB sockets all lie along one edge of the PCB. CON5, CON6 and CON8 are on a narrow neck without any surrounding components. That makes fitting those sockets easier. The other sockets (CON3, CON4 and CON7) are near the relays and buck circuitry around Q3. Since these components are only needed for the power testing and not connectivity testing, we can fit those other components after confirming the USB sockets have been soldered correctly. So, no components below the rows of resistors and above the sockets should be fitted until later, except for the two other surface-mounting parts, the 220mW resistor and the inductor L1. These are low in profile and can be fitted with the other surface-mounting parts to simplify the workflow. Enclosure Prepare the case lid as the first step because the LCD is needed to perform our initial diagnostic tests, and we need to align all the parts to fit the LCD headers accurately. Refer to the cutting diagram, Fig.4. The single 4mm hole at upper right is for access to pushbutton S1; we suggest reading the Options section below to determine if you wish to fit it (and thus whether this hole is needed). It's essential that the opening for the LCD is centred horizontally to avoid the connecting header being skewed. We used a technique that requires a sharp hobby knife, pliers (preferably wide-nosed), a hacksaw or jigsaw and a drill. You can use the bezel as a template, keeping in mind that the bezel will hide most imperfections in the top panel. Mark the edges of the hole on both sides; small holes drilled in the very corners of the cutout area will help to align the two sides. Firmly score the rectangular cutout 86 Silicon Chip Fig.3: the only parts that are somewhat tricky to fit are the USB sockets. Make sure that IC1, RLY1, RLY2, the diodes and Mosfets are orientated as shown. Note that there is a single 10kW resistor amongst the rows of 1kW parts. The USB Cable Tester might still work if you mix this up, but it will drain the battery much more quickly. The six USB sockets are located along one edge of the PCB. It is important to fit USB-C socket CON4 before the relays and associated parts are mounted on the board, so you have decent access to its pins. Tactile switches with long actuators can be hard to come by, although you can certainly use such a part if you can find it. Our assembly uses four wires to stand S1 off the PCB so that you can access it from outside the case. Australia’s electronics magazine siliconchip.com.au Fig.4: fortunately, the laser-cut bezel hides any small inaccuracies in the large rectangular cutout in the case. The LCD mounting holes must be drilled accurately to ensure that the LCD aligns with the PCB underneath. The hole marked in green is used for accessing S1, and is optional. As scrolling text can be hard to read at some LCD contrast settings, the revised firmware (C/D) halves the scroll speed and provides a hidden option 4 under calibration to adjust it (1 = original speed, 2 = default, 4 = extra slow). Kits sent after 4/11/21 have this revised firmware. with the hobby knife against a straight edge. Take care with this, as a slip with a sharp knife can really hurt you! Make a hole in the centre of the rectangle that's large enough to accept the saw blade, then use the saw to cut up to the scored edges. You'll need to make a number of these cuts around the edge to divide the rectangle into manageable pieces. Then carefully flex the plastic to snap it along the score lines and break out the centre area in small sections. If the score lines are accurate, the result will have neat, precise edges. Use the hobby knife to lightly shave small pieces of plastic from the edges of the hole to enlarge the hole if necessary and to tidy up. Another method is to drill a row of holes inside the periphery of the marked area to remove most of the plastic, then file the edges smooth until the LCD fits. This is slower but requires fewer tools. With the LCD in place, you can use it (or the bezel) to mark and drill the location of the four mounting holes. If your LCD doesn't have a pin header fitted to its underside, solder it now. When the screen comes with a header, it's usually supplied siliconchip.com.au separately. Try to keep the pins at right angles to the LCD's PCB to ensure that they will fit squarely into the header sockets on the main PCB. Mount the bezel to the outside of the lid with the four 15mm-long M3 machine screws, keeping the matte surface facing out. Secure on the inside with four nuts. While simplifying assembly, these nuts also provide the spacing necessary to clear the top of the headers on the LCD panel. Slide the LCD module over the machine screws and secure it with the remaining M3 nuts. The top of the LCD panel should sit just proud of the bezel on the outside of the lid. You can see this in our photos at the end of the article. Using four self-tapping screws, secure the main PCB to the other half of the case. This will allow us to align the headers to the LCD and solder them in exactly the right place. There should be a 20mm gap between the main and LCD PCBs when the case pieces are assembled. Note that the enclosure will only fit together one way, so check that it slots together with the LCD1 pads on the PCB in line with the LCD panel's pins. If the LCD panel's pins are Australia’s electronics magazine above the USB sockets when the case is assembled, remove the PCB and rotate it by 180°. If you have 20mm spacers, you might like to use them (and the three mounting holes on the PCB) to align the LCD. Doing it that way is less fiddly. Before proceeding, check our photos of how the header sockets are fitted to the main PCB. Note that they only occupy the six end positions of each end of the header; the four central positions are not connected (as they are not used in the LCD's four-bit mode). Separate the case pieces and slot the sockets onto the LCD's pins as described above. Then place the two case pieces back together. This should align the socket pins into the pads on the main PCB. If you are having trouble, try aligning one edge of the case and pivoting the other end closed. This will bring the pins into location one at a time. With the pins located, screw the case halves together to secure everything in place. Then use your soldering iron to tack one pin to the main PCB at each end of the two headers (four pins in total) through the side opening. This is easiest at the end near the top of December 2021  87 Using the finished USB Cable Tester is as easy as plugging one end of a cable into a Downstream Facing Port, the other end into an Upstream Facing Port and then checking the LCD for its assessment. the PCB. Once you are happy they are secure and still correctly aligned, disassemble the case. Now solder the remaining pins without disturbing the alignment and then refresh any pins that might need it. At this stage, you should be able to reassemble the two halves with the pins lining up and seating into the header, pivoting the case as described earlier. If you're having trouble with the alignment, you could instead join the LCD to the main PCB with ribbon cable, strands of hookup wire or similar. Keep in mind to follow the correct pin ordering and use at least 5cm of cable for each connection to allow for flex when the case halves are separated. Remove the main PCB from the case to continue the construction. To simplify testing, we recommend detaching the LCD from the lid to allow the bare PCB to be attached to the LCD and powered up later while allowing access to the test points and jumpers on the PCB. Soldering the USB sockets Some of these are surface-mounted, so the usual collection of SMD tools is required. With CON4 and CON6 being some of the finest pitch parts we have worked on, a magnifier is a necessity, as is a good source of bright light. A mobile phone camera set to a high digital zoom level is an excellent alternative to a magnifier. 88 Silicon Chip You should also have a fine-tipped adjustable soldering iron, flux (preferably paste) and tweezers. Fortunately, most of the USB sockets (except for CON8) have locating pins, making exact positioning easy. Your flux should recommend a solvent to use for cleanup. Some desoldering braid (solder wicking braid) is a cheap and handy thing to have on hand for fixing any bridges or other situations where there is too much solder. Remember that flux can generate smoke. Use a fume extraction fan or work outside if necessary. Working outside is another way of getting decent illumination. Start with the mini-USB socket, CON5. Apply flux to the pads, rest the part in place (locking its plastic pins into the PCB holes) and apply a bit more flux to the top of the pins. Ensure that it is flat against the PCB. Also try to keep the part square and parallel to the PCB so it will align correctly with the front panel. Clean the iron's tip and apply some fresh solder to it. Then apply it to the point where the pins meet the pads. If you can't get in close, try applying the iron to the extended pads and allow them to draw solder off the iron tip. If you get a good fillet at the point where the pin meets the pad, then all is well. Do the remaining pins, then turn up the iron slightly to secure the mechanical pads. Clean the tip and Australia’s electronics magazine add fresh solder as needed. Pay attention to the mechanical pads, as these sockets will see a rough life and be subjected to repeated insertions and removals. There is also a through-hole pad accessible from the reverse of the PCB to help secure the shell of this part. Flip the PCB over and apply the iron to the pad. Gently feed in solder until the hole fills up. There should already be flux present if you have used it generously; if not, add a little more. Now use the same technique for CON8, the micro-USB socket. It has no locating pins, so you will have to take extra care with its alignment. Its front should be parallel with CON5 and its pins centred in their pads. Work one pin at a time to avoid bridges. If you get a bridge, remove it with extra flux and solder braid. Like CON5, turn up the iron to solder the larger mechanical pads. There are also extra pads underneath the PCB to help secure CON8; solder these similarly. CON4 and CON6 are the trickiest part of this build; the other two remaining USB sockets (CON3 and CON7) are through-hole only parts. The most significant trouble we had with pins on these parts bridging was when solder crept up to where they sit closer together, near their tops. If you keep your iron down near the PCB and just on the PCB pads siliconchip.com.au before you get back to soldering. Use your magnifier to examine the cleaned PCB. Any faults you can pick up now will be easier to see and repair before more components are fitted and may be more apparent now that the flux has been cleaned up. If you're unsure about your soldering, use a multimeter to check for continuity between the bottom ends of where the 26 1kW resistors will be fitted in the middle of the PCB, since these all go back to the USB sockets. If you find any short circuits, you can use the circuit diagram and overlay to identify the affected connector and pins. Through-hole parts A close-up view of the soldered pins on some of the USB sockets. This is what you want the solder joints to look like; glossy, with clear fillets between the PCB pads and socket pins, and no bridges between them. Elongated pads are provided for many of the pins which make soldering them significantly easier. only, you should avoid that problem. Apply flux paste before placing the socket, then add more before soldering the pins. Set up your magnifier to give you a good view, clean the iron tip and apply fresh solder. You'll see that two of the 12 pins have shorter PCB pads; these are not connected in circuit, so they do not have to be soldered. Solder the surface-mount pins, adding flux, cleaning the iron tip and adding solder to it as needed. Inspect your work closely, as it's only possible to easily remove the part and start afresh if the other through-hole pins haven't been soldered. If you think there might be bridges, use more flux and solder wicking braid to remove them. Take care not to allow solder onto the upper parts of the leads. Flux can make inspecting solder joins difficult. You can avoid the hassle of cleaning the entire board of flux for inspection by gently wiping away the flux with a cotton bud dipped in an appropriate flux solvent. When you're happy with the top of the PCB, flip it over and solder the through-hole pins. These are closely spaced too, but surface tension should keep the solder where it needs to be, and you can also use solder braid to remove bridges here. Turn up the iron and solder the four mechanical mounting pins. For these, siliconchip.com.au more solder is definitely better than less. Add some solder to the two central pads under the connector to help with mechanical strength. It might look like two pairs of the through-hole pins on each of CON4 and CON6 are bridged; the two outermost pairs in the row of eight. This is fine as they are all connected to their respective socket's GND pin. You can check this against the circuit diagram and overlay. We suggest leaving CON3 and CON7 until you can complete the self-tests, which will involve getting most of the USB Cable Tester functional. You can fit inductor L1 and the 220mW resistor now. Neither is polarised, so apply flux, rest the part in place and tack one lead with the iron. You may need more heat on L1 due to its size. Solder the second lead on each part, then go back and refresh the first lead if necessary. Now is a good time to clean up any flux that may be present on the PCB, given that all the surface-mounting parts have been fitted and there will be little need for more flux paste to be used. This will allow closer inspection of your soldering. Your flux should recommend a cleaning agent, but isopropanol or methylated spirits are good alternatives. Ensure that the board is allowed to dry and that any flammable solvents have a chance to evaporate Australia’s electronics magazine Continue by fitting the resistors, referring to the overlay diagram (Fig.3) as a guide. Fit the four 10kW parts first, then the 28 1kW resistors, then the rest. Check the resistances with a multimeter if you are not confident of the part markings. The 100W, 1kW and 10kW resistors only differ in one colour band. Once identified, solder them in and trim the leads close. To get the LCD operating so we can run the tests, we need to fit all the parts above and including IC1, except S1 and S2. If you don't have a pre-programmed microcontroller, you should install CON2 to permit programming in-circuit. Now fit D2, the 100nF capacitor near IC1, 10kW trimpot VR1, Q1 and CON2 if needed (we recommend a vertical header for CON2). Be sure to align Q1 and VR1 to the silkscreen pattern. Also solder the battery holder to CON1, running red to + and black to −. Check that D2 is a 1N5819 and that its cathode stripe faces as shown on the silkscreen. You don't need a header at CON1; you can solder the wires to the pads. The holes near CON1 are for strain relief, so thread the battery leads from below the PCB into the tops of the holes and then solder from below (see photos). While there is room to fit a socket for IC1, we don't recommend you use one. For a start, the large number of pins will make fitting and removing IC1 tricky. We only used one to allow us to test different microcontrollers. Gently bend IC1's pins to slot into the PCB, making sure that the pin 1 marker goes to the left as shown. Tack down two pins on opposite corners December 2021  89 Screen 1: on reset, the calibration prompt is displayed. This splash screen is shown for seven seconds. Calibration mode is entered if the USB Cable Tester receives an ESC character via the CON9 serial header during that time. and check that the part is flat and orientated correctly. Adjust if needed and then solder the remaining pins of IC1. If you don't have a pre-programmed chip, program it now, as described below. Otherwise, skip ahead to the Testing section. Programming Install cells in the battery holder to power the circuit (unless you have a programmer that can supply up to 25mA at 4.5-5V). You can use a PICkit 3, PICkit 4 or Snap programmer. We use the MPLAB X IPE for programming; it can be downloaded (along with the MPLAB X IDE) from www.microchip.com under the "Tools and Software" tab. Select the PIC16F18877, click "Apply", select your programming tool and click "Connect". Open the HEX file "0410821C.HEX" using the "Browse" button and then press "Program". If you see a "Program and Verify successful" message, all is well. Otherwise, check the wiring and soldering around the five tracks that go to CON2 from IC1. Two of the programming pins (PGD and PGC) are also used for probing the USB sockets at CON3 and CON4, so make sure that they are not shorting to anything else. If you have a PIC16F18875, use the "0410821D.HEX" file instead. Our original prototype used a PIC16F18875, which is why the PCB is marked with this part number. We decided to standardise on the PIC16F18877 as we think it will be more useful in the future and doesn't cost much more (it has more room for expansion). Though they are from the same family, some of their special function registers are in different locations, so the HEX files are not interchangeable. When finished, detach the programmer and power down the circuit (eg, by removing the cells). 90 Silicon Chip Screen 2: the Calibration screen has four options which are accessed by sending a 1, 2, 3 or 4 character. Sending Ctrl-C at any time will exit calibration mode. The measured battery voltage is displayed at top right to assist calibration. Testing Plug the LCD into its headers, apply power and adjust VR1, the LCD contrast control, until the display is legible. You should see a splash screen with a countdown timer, followed by the main USB Cable Tester screen. You can check the contrast voltage at VR1's wiper. Our unit reads around 1V with a fresh battery. If you see a "Ready for cable." message after seven seconds, construction is correct so far, and your USB socket soldering has no detectable faults. The Battery value should be between 4.2V and 4.8V. You can compare this with a multimeter voltage reading between TP1 and TP2; if the reading here is roughly correct but the displayed value is not, the circuit has a problem. If all is in order, you can progress to the remainder of the construction below. Problem? If there is no LCD backlight, there's likely a problem around transistor Q1. If you can light the backlight by grounding the LED cathode (pin 16) of the LCD, then it's definitely the PCB components and not the LCD. If you get a message on the LCD listing the UFP or DFP, these messages will point to USB socket pins that might be shorted. Refer to the circuit diagram and overlay to find those pins. Disconnect the power supply, make repairs and test again until you get the "Ready for cable." message. Remaining components Fit the three remaining capacitors. The two 1000μF and one 10μF electrolytic capacitors all have their positive (longer) leads facing to the right, according to the PCB silkscreen. Slot the two remaining USB sockets (CON3 and CON7) into place. Tack a couple of leads and ensure that the parts are flat against the PCB and squarely aligned to the PCB. This Australia’s electronics magazine will help align the sockets to the front panel. When the sockets look correct, solder the remaining pins and be generous with the mechanical tabs to ensure they have the necessary strength. There are two more diodes. Fit the single 1N4148 near CON4; it will sit between the two relays and is easier to fit before them. Check that its cathode stripe aligns with the silkscreen markings. The remaining diode is D3, a 1N5819 near L1. Then fit the two relays, RLY1 and RLY2. They should have one end marked with a stripe that will match the line on the PCB at the end nearest to IC1. As for any multi-lead part, solder a couple of pins and check that the device is correctly positioned before soldering the remaining pins. Then fit the other 2N7000 Mosfet (Q2) near RLY2 and Q3, the larger TO-220 P-channel Mosfet, near L1. Its marked face should be towards L1 with the tab closest to the cutout in the PCB. Ensure Q3's leads are pushed down against the board so that it doesn't foul the enclosure lid. Options The remaining parts are optional and only really needed for calibration (which isn't required). However, as we noted in the first article, you can also use S1 to wake up the USB Cable Tester without plugging in a cable. This could be handy if you are often testing just one end of a cable. The UART header, CON9, is only needed to enter calibration mode via a USB-serial module. S2 can be used to reset the microcontroller and quickly jump in and out of calibration mode. JP1 and JP2 are used to calibrate out the resistance of the internal wiring and traces. Our HEX file is calibrated with values suitable for the parts we are supplying, so there is little need to do this if you are building it from our kit. siliconchip.com.au Screen 3: each calibration value is entered in decimal. The value can be accepted by pressing Enter (CR, ASCII code 13) or cancelled by pressing ESC. You can clear the last keypress with delete or backspace. The other two calibrations are for the microcontroller's internal 1.024V reference voltage and current sense shunt resistance. The internal reference is specified to be accurate within ±4%, so the USB Cable Tester will be perfectly functional without calibration, but it will be slightly more accurate if this is done. The current sense resistor should be within 1% and won't need adjustment. The measured voltage is around 100mV with 1mV resolution, so the shunt resistance only needs to be adjusted if you can't use the specified shunt value. Values from 100mW to 500mW should work, although we have only tested the specified 220mW value. Lower values will give less accuracy, while higher values reduce the headroom to measure voltage drop in cables. Since the optional parts are supplied in our kit, you might as well fit them all if you already have them. Fit CON9 with the pins facing up; this will allow a pair of jumper wires or similar to be connected between the USB-serial converter and the PCB. Fit the JP1 and JP2 headers but leave the jumper shunts off for now, or plug them onto just one pin of the header. S2 fits flat against the PCB as it is only used for setup and calibration. It shouldn't be accessible during normal use. Snap it into the pads and ensure it is flat against the PCB before soldering. If you want to make S1 available for use after calibration, you need to drill the extra hole shown in Fig.4 and mount S1 above the PCB, near the top panel. To align everything, attach the main PCB to the enclosure using one screw in each corner. Use lengths of tinned copper wire to attach S1 to the PCB. Align S1 to the inside top of the front panel with some tape or Blu-Tack, then, after placing the lid on top, tack solder one or of the wires in place. This just needs to be enough to locate S1. Remove the tape and the lid. With the better access this provides, add more wires to secure the switch on all four corners. If you don't need external access for S1, it can be simply soldered flat against the PCB like S2. This completes the soldering for the USB Cable Tester. Double-check your work, then plug the LCD into its header. Calibration If you wish to perform calibration, connect a USB-serial converter to CON9 using female-female jumper wires. If you are using a CP2102 type (like us), the pin marked TXD on the converter connects to R on the PCB. GND on the converter connects to "−" on the PCB. Only one data line needs to be connected as the USB Cable Tester displays its prompts and responses on the LCD instead of the serial terminal. Screen 5: while the value is being saved to EEPROM, it is also displayed as a final check before returning to the main Calibration screen. siliconchip.com.au Screen 4: there is a final confirmation prompt before an entered value is committed to EEPROM. To answer the prompt, enter either upper or lower case "Y" or "N". Open a serial terminal program (eg, TeraTerm) and connect to the USB-serial converter at 9600 baud, 8 bits, no parity, one stop bit (8N1). It won't matter if your USB-serial converter has 3.3V or 5V signals. The 1kW resistor will limit the current flow, and IC1 will recognise logic levels in this range. Now power up the USB Cable Tester PCB. When the prompt shown in Screen 1 is visible, press the ESC key on the serial terminal. If communication is working correctly, you should see Screen 2. If not, check your wiring and reset the micro with S2 to get the prompt to press ESC again. At Screen 2, you can press 1, 2, 3 or 4 on the terminal to change the displayed value, as seen in Screen 3, after which you are prompted to confirm the change (Screen 4) with "Y" or "N". If you press "Y", you will see something like Screen 5. To calibrate the VREF value, measure the supply voltage between TP1 and TP2 and compare this with the displayed voltage shown at top right. The internal voltage reference is in inverse proportion to the displayed voltage. So if the displayed voltage is 1% too high (for example), increase the VREF value by 1% of its current value. With the internal reference specified being accurate to within 4%, you should not need to change this up or down by more than 40 points. Another way to calculate this is that Screen 6: with JP1 and JP2 fitted, only the Tester's internal resistance is reported. The value at the bottom of the screen is the contact resistance value. A similar screen is seen when a power-only cable is plugged in for testing. Australia’s electronics magazine December 2021  91 Screen 7: once calibration is complete, the main idle screen is shown unless a cable is plugged into the ports. The battery condition is reported and the sleep timer counts down 10 seconds before entering low-power sleep mode. an error of 0.01 in the displayed voltage (ie 10mV) is equivalent to about 2.1 VREF steps. So if the displayed value is 4.68V instead of 4.65V, add 6 points to the VREF value. The nominal shunt value should be accurate enough. You can measure the shunt resistance any time the relays are inactive (all the time in calibration mode) and there are no cables plugged in. Measure between TP1 and TP3. To calibrate the relay contact resistance, use option 3 to set this to 0mW. Then exit calibration mode by pressing Ctrl-C on the terminal or resetting the microcontroller. Attach jumper shunts to JP1 and JP2. This will simulate a power-only cable being connected, and you should get a display like Screen 6. Note down the resistance value shown, then remove the shunts. Reset the micro again and go back to calibration mode with ESC on the terminal. Save the noted value as the contact resistance and exit calibration. If you reattach JP1 and JP2, you should see a value very close to zero. At this stage, you can try out the USB Cable Tester on any USB cables you have lying around. See the Usage section for further information. Screen 8: a typical test result on a USB-C to USB-C cable shows what is expected for a fully USB 3.2 compatible cable with two SuperSpeed lanes, meaning that it has the USB 2.0 D+/D− pair as well as the SuperSpeed wires. Final assembly Power down the unit by removing the cells, detach the LCD from its header and reattach it to the lid as described earlier. Put the front panel PCB over the USB sockets on the main PCB and slot the pair of PCBs into place in the base of the enclosure. Secure the main PCB to the enclosure using the eight self-tapping screws. There are solder pads on the inside of the front panel PCB, so the panel can be affixed to the main PCB by soldering these pads to the USB sockets. The battery holder may have screw holes, but to avoid marring the underside of the enclosure, we recommend gluing it with neutral-cure silicone or construction adhesive. If you do use screws, fit self-adhesive rubber feet to the underside of the box to prevent the screws from scratching any surfaces. Slot the rear panel supplied with the case in place, then fit the cells. Carefully position the enclosure lid, feeling that the LCD header locks in place. The LCD backlight may illuminate if the unit has not gone to sleep, but there won't be a meaningful display since the LCD controller will not have been properly initialised. Allow the unit to go to sleep (the LCD backlight will go off), then plug in a cable (or press S1) to wake it up; this should reinitialise the LCD, and you should see one of the cable reporting screens (or the idle screen). If this is the case, all is well, and you can secure the two halves of the case with its two included screws. Usage Screens 7-11 show the USB Cable Tester in use. Screen 7 is the idle screen which shows the battery condition and time until the unit enters low-power sleep mode. It is present when the unit is awake, but no cable is detected. Once a cable is inserted, you should see the full diagnostic display, as seen in Screen 8. The first line shows a broad pass/fail assessment of the cable. The second line identifies the USB rating and the number of short circuits (+) and open wires (-) that have been detected. For an OK result, these are both zero. The third line shows more detailed information depending on the test results, listing the wires involved in any short or open circuits detected. The text may scroll if it doesn't fit on one line. The header on the LCD screen aligns with two 6-pin sockets on the main PCB. 92 Silicon Chip Australia’s electronics magazine siliconchip.com.au Screen 9: the Cable Tester will elicit a variety of information about a faulty cable, including what it thinks it ought to be and what problems it might have. Here, an open GND wire means that the cable will not function, even for charging. As shown in Screen 11, the results of the UFP and DFP tests are summarised so that single-ended tests may be carried out. This is done by unplugging one end of the cable at a time, leaving just the UFP or DFP connected. It's common that the DFP and UFP tests will detect that GND is shorted to the shield. This is the case for some USB-C cables and doesn't seem to cause any problems. The final line summarises the results of the current pulse test. Values around 200mW can be expected for cables in good condition. Up to around 500mW, they could work fine, especially for light loads; higher values indicate a cable that may cause problems. You can test cable combinations, such as when a cable is supplemented by a USB extension cable. However, as we noted, high-speed signal integrity is not tested by the USB Cable Tester. If you want to check a USB extension cable, first test a cable with a plug that will fit into it on one end (ie, A-type or C-type) and a B-type or C-type on the other; ideally, a USB 3.2 SuperSpeed type, although you can still do the test if you don't have one. Verify that cable is good and note its type and resistance. Then plug that cable into the extension cable and test the combination. Subtract the resistance reading noted earlier from the new reading to measure the extension cable's own resistance Screen 9 shows what might be seen if the cable has a fault; the first line indicates this. The second line lists the nearest 'working' cable type to what has been detected and also the number of faults present; in this case, '1-' means that this is most likely a USB 2.0 cable but with one conductor open circuit. The third line indicates that the open wire is the GND conductor, so it is unlikely to work at all. The "High resistance" message is only shown when the cable is incapable of carrying siliconchip.com.au Screen 10: with USB-C cables being reversible, it's necessary to test them with both insertion orientations. If this screen is seen, the current orientation does not connect the D+/D− pair and you should try another orientation. the lowest 100mA test current. The display in Screen 10 needs some explanation. USB-C leads only have one D+/D− pair (the wires required for a legacy USB 2.0 connection) but can be plugged in one of two ways, and some cable orientations do not detect this pair. In this case, the USB 3.2x2-2.0 indication is shown. That means that two of the SuperSpeed lanes needed for a USB 3.2 connection are detected, but the USB 2.0 wires are not. For these cables, you must try each USB-C plug both ways around (rotated 180°). If only one end is USB-C, run the test one way and flip it to try the other. If you have USB-C at both ends, flip one end, flip the other, then flip the first end back; this will test all four plug orientation combinations. You should get a USB 3.2x1 or USB3.2x2 result for only one of these tests, with the USB 3.2x1-2.0 or USB 3.2x2-2.0 indication for the remainder. That is, unless your cable has an extra D+/D− pair, which is non-standard, but it could still work on some devices. If all the combinations show USB 3.2x1-2.0 or USB 3.2x2-2.0, there is a problem with the D+/D− pair either being missing or open-circuit. The x1 designation means one SuperSpeed lane is present, while x2 means two lanes, which is only possible with a USB-C to USB-C cable. Screen 11 shows a typical UFP-only test result. If short circuits are detected in both the UFP and DFP simultaneously, but no continuity is detected between the two ends, then the UFP and DFP screens will alternate. This either means that your cable has failed very badly or (more likely) you have two different cables plugged in. For Screen 11, one end of an OTG cable has been plugged in. The fourth line shows a specific message for this case – it has detected that the GND and ID wires are connected. Only short circuits are shown on this screen, as usually, there should be no connections between pins. If four or more pins are listed, they might not all be shorted together, but they will all be shorted to at least one other pin. Up to 11 wires can be displayed, so there might be more than those shown if the screen is full. Also remember that you must always connect a cable between one of the UFPs and one of the DFPs. For example, a normal USB-A to USB-C cable can be plugged into the two DFP sockets, but this will not give a meaningful result; the USB-C end should instead be plugged into the UFP socket. Conclusion With this comprehensive and easyto-use piece of test gear, you can now sort through all your old USB cables and see whether they are worth keeping. With a 30μA sleep current, the USB Cable Tester will happily sit for years on the shelf, always ready. For a final flourish to your USB Cable Tester, you can carefully apply some white acrylic (or similar waterbased paint) to the etched text on the front of the LCD bezel. Wipe the excess away with a damp cloth and SC allow to dry. Screen 11: a typical use for the single-ended cable tests is checking if OTG cables correctly ground the ID pin. Here we see that is that case, with a specific message provided on the bottom line. Australia’s electronics magazine December 2021  93