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• Monitor up to 3 batteries from 6 to 100V • Currents to 10A (or 100A+ with shunt) Versatile Battery Multi-LOGGER Part 2 – By TIM BLYTHMAN WITH TOUCHSCREEN LCD In Part 1 of our new Battery Multi-Logger last month, we described how it combines the functions of a Micromite LCD BackPack along with voltage and current sensing hardware, and power-saving techniques, all on a single PCB. Now we’ll go over the construction, testing, setup and calibration procedures so you can build and use it. B • • • • efore getting to the assembly instructions, let’s quickly review the Logger’s capabilities. It can handle batteries from 6-100V and monitor up to three bidirectional currents of up to 10A using its onboard shunts, or much more (to 100A or beyond) using external shunts. Its own power consumption is less than 1mA while actively logging with the screen off. It can display the current and historical data on a 2.8-inch backlit LCD touchscreen, and the data can also be downloaded to a computer over USB for further analysis. It tracks the current battery stateof-charge in both amp-hours (Ah) 84 Silicon Chip and watt-hours (Wh), and it has a current measurement resolution of around 0.1% of full-scale, which equates to 10mA steps when using the internal shunts. All of these functions are built onto a small PCB. As all the user interface features are accessed via the touchscreen, it can easily be integrated into other devices through a rectangular cutout in the case. Construction The Battery Logger is built on an 86mm x 50mm double-sided PCB coded 11106201. Fig.5 shows where the components go, on both sides of the board. As usual for assembling a board Australia’s electronics magazine with many SMDs, it is useful to have the following on hand: flux paste, solder braid (wick), a magnifier, tweezers and an adjustable temperature iron. The smallest parts have pad spacing under 1mm, so solder bridges are almost inevitable, hence the need for flux paste and solder wick. Since flux tends to generate smoke, use a fume extraction hood or work in an outdoor area, where the smoke can more easily dissipate. One of the most fiddly parts is the USB socket, CON5, so start by fitting that. Dispense flux onto the pads and then sit the USB socket in place; it should lock into the holes in the PCB. Add some more flux to the tops of the pins. siliconchip.com.au The Multi-Logger can be mounted in a UB5 Jiffy Box like many Micromitebased projects and as seen here. But you might like to use the bezel to mount the Multi-Logger in the front panel of your equipment enclosure; you could then use the Jiffy Box to protect the rear of the unit. With a clean tip, add solder to your iron, then press it against the small pins and pads together. The socket’s metal shroud tends to get in the way a bit. Once you are sure that you have soldered all the pins, check for bridges and remove them if necessary, then solder the larger tabs on the shroud in place. ICs Solder the ICs (IC1-IC6 and REF1, on the back of the PCB) next. We suggest fitting IC5 first, as it has the finest pin pitch. For each of the ICs, check the orientation of pin 1 against the PCB silkscreen by matching the dot before soldering any pins. IC6 is asymmetric, so although this part is small, it is easy to orientate correctly. Note that some of the ICs might not have a dot to indicate pin 1. Instead, they will have a bevel along one edge or a line at one end; in each case, this feature is nearest to pin 1. For REF1, the pin 1 indicator might even be a tiny laser-etched cross. When soldering the ICs, apply flux to the pads, then rest the IC in place and tack one lead. Check the positioning, ensuring that the part is flat and aligned within its pads. If not, remelt the solder and adjust the part with the tweezers. After the part is located correctly, solder the remaining pins. Don’t worry about solder bridges as they happen, as it is easier to remove multiple bridges later, all at the same time. Apply exsiliconchip.com.au tra flux if necessary during soldering. To remove bridges, apply fresh flux and press the solder braid against the excess solder with the iron. When it melts, allow it to draw up the solder and then gently pull it away from the component. The surface tension between the component and the pad should hold enough solder to maintain a good connection, even if the solder braid removes most of it. Now is a good time to inspect your work closely with a magnifier, as making changes will be harder as more parts are added. It’s a good idea to clean away excess flux first; isopropyl alcohol is a good all-round choice, but specialised flux cleaning products often do a better job. Transistor and regulators The next trickiest parts are the transistors and regulators in SOT-23 packages. There are six such parts in three types: Q1 & Q3 (P-channel Mosfets), Q2 & Q4 (N-channel Mosfets), and REG1 & REG2 (LDO regulators). Fortunately, they will only fit one way, so use a similar technique to the ICs. Solder one lead and check the position before soldering the remaining leads. The remaining SMDs all have much larger pads, so are much easier to deal with. Resistors and capacitors Many of the remaining parts are 3216-sized (3.2 x 1.6mm; or 1206 imperial) resistors and capacitors. The resistors should be marked with their Australia’s electronics magazine values, while the capacitors are typically not, so take extra care with the capacitors and don’t mix them up. We recommend working with one value at a time. Where possible, we’ve marked the resistors and capacitor values below the part itself; the exception is the parts around IC4. Remember that if you are using external shunts for current sensing, you omit the three 15mΩ shunt resistors. Leave the larger shunt resistors aside for now, even if you intend to fit them. For the remaining parts, check the value printed on the silkscreen against the value on the part, which will be a numerical code that you can match in our parts list. For each part, apply flux to the pad, solder one lead, check and adjust if necessary and then solder the other lead. Refresh the first lead if necessary. Most of the capacitors are 100µF, 10µF or 100nF types, so we recommend placing these first. The 100µF and 10µF capacitors will most likely be larger, so they won’t be too hard to differentiate. All four 100µF types are fitted to the back of the PCB. Use the same method as for the resistors. Follow up with the remaining capacitors, taking note of their value before removing from the packaging and working one at a time. There are two small inductors (L2 and L3) which also have 3216 dimensions; they are soldered in much the same way. The larger 120µH inductor (L1) might require a hotter iron to solder. March 2021  85 Fig.5: the PCB photos shown above are of an early prototype, so they differ slightly from the overlays which are our final design, including up-to-date component values. There are components on both sides, although the back of the board is much more sparsely populated. Take extra care with the orientation of all ICs, the two diodes and the LED. Most of the other components are unpolarised. Use the same technique of working on one lead at a time. Sometimes you get better heat transferral by pressing the long edge of your soldering iron tip onto the pad. Then solder the other lead. Next, solder the button cell holder. Again, you might need to turn up your iron to supply more heat. Add flux to the pads and locate the holder such that a cell can be inserted from the edge of the PCB. Tack one pad down and when you are happy with it, solder the other pad. Refresh the first pad to relieve any stress on the PCB pads. Check our photos to see how it should look. And the rest There are two surface-mounted diodes; they are both fitted with their cathodes facing towards REG2 (as that is what they supply!). You may well be using surfacemounting or through-hole parts for LED1 and S1. Fit these two next. LED1’s cathode faces to the right, towards CON1. Most surface-mount LEDs have their cathode marked with a green dot, but double-check this, as some do not. 86 Silicon Chip At this stage, practically all the SMDs have been fitted, so it is a good opportunity to clean off any excess flux left on the PCB. JP1 is not usually needed, so can be left off (we used it in our testing), but JP2 is required. Fit the jumper shunt to make it easier to manipulate and solder one lead. Check it is square and flat, then solder the other leads. If you have pre-programmed microcontrollers (IC1 and IC2), then fit the shunt to JP2 on the bottom two pads (as seen in our photo). This is the ‘RUN’ position. If you need to program IC1, then fit the shunt to the top two pads (near the PCB mounting hole). For programming, you will only need to fit CON1, as IC2 can program IC1. But if you have a programmer, you might find it quicker and easier to fit both for programming anyway. We used right-angled headers for CON1 and CON2 to make it easier to debug, but straight headers will also work, and fit under the LCD. The connections for the 2.8in LCD are made up of a 4-way and a 14-way female header. Only the 14-way header is needed for the current version of the Australia’s electronics magazine software, although having both headers will make the assembly more robust. Use the 2.8in LCD as a jig to fit the headers. You might need to solder pin headers to the LCD if they are not preinstalled; most do not come with the 4-way header fitted. In that case, plug the headers into the sockets and insert them into their respective PCBs. The headers sockets go on our PCB, with the pin headers on the LCD side. Solder the headers in place, keeping the PCBs parallel. Then gently separate the LCD from the PCB, wiggling it if necessary. The final step in assembling the PCB is to fit CON3 and CON3A, the battery and load connections. Mount them on the back of the PCB to allow access even after the stack is assembled. Verify that you have fitted the three larger 15mΩ shunts if you will not be using external shunts. Programming If you have pre-programmed ICs, you don’t need to worry about this step and should proceed to the setup section. Both IC1 and IC2 need firmware to siliconchip.com.au work. The only way to program IC2 in-circuit is to use ICSP header CON1 and a programmer such as a PICkit 3 or PICkit 4. You can use the MPLAB X IPE (integrated programming environment), which is available as a free download as part of the MPLAB X package from www.microchip.com/mplab/mplabx-ide Choose PIC16F1455 as the device and your programmer from the Tool drop-down. Connect the programmer to CON1 according to its instructions and browse for the Microbridge HEX file (2410417A.HEX). Then press the Program button to upload it. With the IPE open, you can also use this to upload the firmware for IC1. Connect the programmer to CON2, select PIC32MX170F256B as the Device and browse for 1110620A.HEX. Upload this file with the program button. After programming is done, don’t forget to move JP2 to the RUN (lower) position. Microbridge and MMBasic If you’re inclined to tinker with the BASIC code, you can program IC1 with the MMBasic files too, although that is a bit more involved. We’ll outline the steps, with the assumption that you have a bit of experience with the Micromite environment, know your way around MMBasic quite well and are comfortable uploading files to the Micromite. If you don’t want to do this, skip to the next section. You will need the Microbridge firmware on IC2 and start with JP2 in the PROGRAM position, as it needs (at the very least) the HEX file for the BASIC environment to be uploaded to IC1 first. This can be done with a PICkit and the IPE (as outlined above), but instead of the Battery Logger firmware, you should choose the latest Micromite MMBasic firmware file. Alternatively, the MMBasic firmware can be uploaded by the Microbridge by pressing S1 (to enter programming mode). Then use a program like pic32prog or P32P GUI to upload the Micromite MMBasic HEX file. We used version 5.5.2. JP2 can now be moved to the RUN position. From the BASIC environment (a serial port running at 38,400 baud), you should run the commands to set up the 2.8in LCD and touch siliconchip.com.au Fig.6: we ran this diagram last month to show what the Logger can do. We’re repeating it now as you might want to use it as a guide when wiring it up. When using the internal shunts, the battery connects across CON3, and the positive ends of your loads or chargers go to the terminals of CON3a. All load and charger negatives go straight to the battery. When using the external shunts, follow diagram (C) and make sure the wiring from the battery to the shunts is short and thick for maximum precision. panel as per usual for a V2 Micromite BackPack. OPTION LCDPANEL ILI9341,    LANDSCAPE, 2, 23, 6 OPTION TOUCH 7, 15 GUI CALIBRATE The BASIC files are arranged as a library file supplementing the main source code. This allows the Micromite to compress some of the data it uses. Load the library.bas file, then run the command: Australia’s electronics magazine LIBRARY SAVE This saves and compresses the library file. Next, load the main Battery Logger.bas file and run it. These instructions are in the library.bas file. Setup and operation If you haven’t already done so, fit a CR2032 cell to the BAT1 holder, fit the LCD panel and connect the Logger up to a computer or USB power supply via CON5. If you programmed IC1 with the hex file specific to this project, March 2021  87 Screen1: the main screen provides all the critical statistics for your battery, as well as three simple menu options for accessing other features. The greyed values seen are capacity calculations which are not yet valid, as the Logger has not detected a complete charge and discharge cycle; they will light up brighter when that happens. then the Logger software should start straight away. If you loaded the BASIC files yourself, you might need to run the program manually for the first time. You should see Screen1 appear at startup. An error message might appear for the first few seconds while the program waits for a valid battery reading to occur; if it does not disappear after about ten seconds, there could be a problem with IC5. The voltage shown after “V=” should be zero, as you don’t have a battery connected yet. You might see some readings for the current values, though, as we have not completed the calibration yet. I1 corresponds to the Logger’s own current use, while I2-I4 are the currents measured through the terminals of CON3A, as shown in Fig.5. These values might jump around a bit, but the long-term averages are the most important figures. At right are the capacity and state of charge measurements. CHGv% is a simple linear calculation between nominal full and empty voltages, while CHGm% is based on measured current since the last full and empty states. The CHGm% reading won’t be entirely accurate until the battery has experienced a complete charge and discharge cycle. Similarly, the capacity readings will not be meaningful right away. At upper right is a countdown timer; when this reaches zero, the display will blank. This is the normal mode, where the Logger is logging, but does 88 Silicon Chip Screen2: the Data screen provides a graphical view of the logged data. Different timespans can be shown, and the display will automatically scroll once a minute to show current data. The Weeks option provides around a fortnight of data. Data can also be dumped as CSV rows over the console serial port with the Export button. not need to display anything, thus saving power. The counter can be reset by touching anywhere on the Main screen. This timeout only happens from the Main screen shown in Screen1, so make sure to return to it each time you finish accessing the Logger’s graphical interface. To reactivate the screen, press and hold the touch panel until the backlight illuminates. For maximum power efficiency, the Micromite only checks the panel at one-second intervals, so it might take a second or so of touch to wake it up. The Logger waits for the touch to be released before displaying the main screen, so you can’t accidentally press a button when waking it up. The interface is fairly intuitive, but we’ll walk through the various screens anyway. Screen2 is reached by pressing the Data button and displays a graph of the voltage and currents. The current scale (left-hand side) can be manually set, while the voltage scale uses the nominal full and empty values. By default these are set to 14.4V and 11.0V, to suit a 12V lead-acid battery. The buttons along the bottom set this page to display the various scales, with the time frames shown at the bottom of the screen. In each scale, the Export button does a dump of data to the serial port. This data is produced so that it can be saved as a CSV (comma separated value) file and then can Australia’s electronics magazine be opened with most spreadsheet programs. Pressing Exit returns to the Main display. Screen3 is accessed using the Settings button. Each value shown can be changed by pressing the respective button. Screen4 shows a number being entered, in this example to update the current year. If the number entered is invalid, a message is displayed. Pressing OK prompts for the new value to be confirmed (see Screen5). The time and date settings are immediately saved to the real-time clock and are displayed on this and the main screen. The two B/L values are for the backlight brightness as a percentage, from 1-100. The first value (B/L) is used most of the time. The second value (B/L dim) is used for the last five seconds before the screen shuts down, to indicate that this is about to happen. A minimum value of 1% is allowed for either setting to ensure that the display is always visible. The V(full) and V(empty) values should be set to suit your particular battery. You can’t set the V(empty) value to be higher than the V(full) value. The Timeout value sets how long the display stays on before blanking at the Main screen. This has a minimum of five seconds, as this is the period of dimming that occurs before blanking. A large value can be used to stop the display blanking; eg, a period of 99999999 seconds is around three siliconchip.com.au Screen3: the Settings screen provides the most common options for configuring the Logger, including battery voltages, time and date and backlight controls. Each entry is validated to ensure it does not conflict with other values (such as the ‘Empty’ voltage being higher than the ‘Full’ voltage) and then immediately saved to flash memory. years. The “I scale” value sets the limits of the graph on the Data page only. Setting a value of 20 will cause the graph to span from -20A to 20A. The “V(sdown)” value sets a critical battery limit. Below this level, the Logger sleeps for much longer periods between activity. The MMBasic code sets this to 15 seconds. Since the ADC (IC5) goes to sleep after each conversion, the result is that current consumption drops even lower than the normal ‘screen off’ mode. This setting is intended to preserve a battery that already is heavily discharged. You can still use the Logger, although you will have to touch the screen for up to 15 seconds to wake it up, and the data will be much more sparse, as it won’t be logging as frequently. Still, you should be able to quickly identify that there is a problem with the battery and rectify it. To disable this feature (eg, for testing without a battery connected), set this value to 0V. In this case, the buck regulator will shut down below around 5.5V, causing the Logger to power off completely unless it is powered from USB. Calibration The remaining button on the Main page goes to the Calibrate page (Screen6). You should always calibrate the V factor first, as the measured current depends on the voltages measured being accurate. siliconchip.com.au Screen4: the Entry screen is displayed whenever a number needs to be entered. The symbol at lower left allows the last typed character to be deleted. Since negative numbers are not used, there is no minus symbol. Internally, there is a V factor (the ratio between the actual voltage and the raw 24-bit ADC reading) for each of the four dividers, but only one is displayed, as they should all be similar to within component tolerance. The nominal value is 100V/16,777,216; ie, a full-scale reading at 100V. The four V factors allow compensation for variations in the dividers, mostly due to component tolerances. They allow the three current sense dividers to be zeroed against the primary voltage divider. Thus, this step should be done first before attempting to calibrate the individual currents; otherwise, there will be an offset from zero. You’ll need to hook up your battery, or, at the very least, a stable voltage source above 6V. Higher voltages will mean that the quantisation error (due to steps between consecutive ADC values) will be proportionally less, potentially giving slightly better calibration. Don’t hook up anything to CON3A though, as we don’t want any current flow to skew the results. If possible, leave the USB supply connected too, as this will minimise the load on the battery, with the display running from USB power. In this case, the only battery drain will be the no-load quiescent current of IC4, at around 10µA. Hook up a voltmeter to the battery terminals and allow the unit to settle for a minute. This reading must be stable for optimum results. Press the “Volts” button and acknowledge that Australia’s electronics magazine there is no load on the terminals. Enter the battery voltage as displayed on the voltmeter. A page will show the various V factors and an estimate of how much they vary. If there is a variation of more than a few percent (due to component tolerances), you might have a problem with the dividers, such as a wrong component value or a spurious load on the battery. You can confirm the new values by pressing OK, or use Cancel to investigate further. The calibration is stored to flash and used immediately. Go back to check that the displayed currents (I2I4) have settled near zero. This means that the calibration is correct. The remaining calibrations are not so critical as they won’t produce an offset in the results, but will simply give incorrect current scaling. The default values are calculated from nominal component values; you will have to change these if you are using external shunts. Current calibration The current calibration method is straightforward. A known load is applied to each terminal, the current is measured and entered into the Logger, and it then calculates the conversion ratio. For I2-I4, these are the external loads at CON3A, while I1 is the Logger’s own current. Thus for I2-I4, the load should be applied between CON3A and the battery negative. March 2021  89 Screen5: each Entry value is validated before being processed and saved to provide a way of safely making changes. In this case, the actual current being displayed on the main screen will be negative (the battery is discharging). Still, you can only enter a positive value, so you should just enter the magnitude of the current. The initial values are set in the MMBasic program but can also be altered here, which you need to do if you are using shunts with values other than 15mΩ. The current calibration values are simply the inverse of the shunt resistance in ohms, so the default 15mΩ shunts have a calibration factor of 66.67. For I1, you will probably need to disconnect the battery to allow an ammeter to be connected in the Logger’s supply. When doing this, disconnect the USB cable and ensure there is no load on any of the CON3A terminals. The nominal value of the factor used for I1 is the inverse of the shunt resistor resistance (in ohms) divided by the op-amp circuit’s gain. Consider that the measured shunt voltage would be the same as if the shunt resistance was multiplied by the gain. So the default value is the inverse of 0.1Ω, (ie 1/0.1) = 10, divided by 100, or 0.1 Screen6: the Calibration screen provides a mostly automated way of adjusting the Logger to account for component tolerances. The operator simply needs to enter a meter reading (volts or amps), and the Logger calculates the calibration factors to produce the desired value. In this form, it can be mounted in a box. Still, we expect most people will use the acrylic panel as a bezel to mount the Logger in an equipment enclosure, with wires connecting internally and the touch panel being accessible from outside. To do this, separate the LCD and Logger PCB by wiggling gently. Decide which side of the bezel you would like visible; we prefer the matte face, but it is reversible, so you can put the gloss side to the outside if you want. Thread four of the M3 screws through the front of the bezel, place the washers over the threads, then follow with the LCD. The spacers provide clearance for the leads that protrude from the back of the headers. Secure the M3 screws with the tapped spacers. Reconnect the Logger PCB and secure it to the stack with the remaining M3 screws. This complete assembly can now be attached, for example, to the front door of an equipment cupboard, using an M3 screw and nut in each corner to secure it. When the cabinet is opened, the battery connections can be accessed from the rear. Protecting the back of the Logger is easily done with the UB3 Jiffy box. The included screws might be too short if they need to screw through a panel, but the pillars will line up with the holes in the bezel. Mounting and completion With everything calibrated and set up, you can mount and connect up the Battery Logger. Being a similar size and shape to the V2 Micromite BackPack, the Battery Logger can be fitted with the laser-cut acrylic front panel designed for UB3 Jiffy boxes. 90 Silicon Chip When fitted to the inside of an equipment enclosure, the important features are available for maintenance access, including cable terminations and the RTC backup battery. Australia’s electronics magazine siliconchip.com.au Screen7: any conditions that need to be satisfied for accurate calibration are prompted before the calibration begins. While this adds an extra step, it means there is little chance for the calibration to fail. In this case, all you need is a few holes in the side or back of the box to run the wires. To complete the wiring, you can follow the three examples shown in Fig.6 (reproduced from last month). This shows options for use with internal and external shunts, including one possibility of sharing terminals on CON3A if you have more than three total loads plus charging sources. There should ideally be a fuse on each wire out of CON3A (or in the high-current wiring leading to the shunts). There should also be a fuse in the wire leading from the battery posi- Screen8: as noted, all values are checked for validity before being saved and used by the Multi-Logger. In this case, a brief but helpful message is provided to allow the user to work out what went wrong. tive to CON3’s positive terminal. This way, a fault in the Logger or any of the connected loads cannot short out the battery. The wiring will be specific to individual arrangements, so we can only offer general advice. in the future. You will see that we haven’t left many microcontroller pins unused, but we have broken out two pins to a header at the top right of the PCB. These are connected to the Micromite’s I2C pins, as we figured that would be a good way of expanding the device (they are already used for the real-time clock, but I2C is a shared bus). 3.3V power and ground connections are also available at nearby CON2, while CON6 connects to the Micromite’s second COM port (COM1), at pins 21 and 22. That provides a dedicated communications channel that could be used SC to add more features. Conclusion Like many of our projects, especially those written in MMBasic, we expect people will want to customise, tinker and perhaps improve the software. We look forward to hearing what features readers would like to add, as we are already planning to supplement the Logger with extra hardware OR T HI S : T HI S . . . Every article in every issue of SILICON CHIP Can now be yours forever in digital (PDF) format! Nov 1987 Dec 2019 n High-res printable PDFs* n Fully searchable files - with index n Viewable on 99.9% of personal computers & tablets * Some early articles may be scans Software capable of reading PDFs required (freely available) Digital edition PDFs are supplied as five-year+ blocks, covering a minimum of 60 issues. They’re copied onto quality metal USB flash drives (at least 32GB). Just order which block(s) you want! n Nov 1987 - Dec 1994 n Jan 1995 - Dec 1999 n Jan 2000 - Dec 2004 n Jan 2005 - Dec 2009 n Jan 2010 - Dec 2014 n Jan 2015 - Dec 2019 Each five-year block is priced at just $100, and yes, current subscribers receive the normal 10% discount. If you order the entire collection, the 6th block is FREE (ie, pay for five, the sixth is a bonus!). All PDFs are high resolution (some early editions excepted) and the USB Flash Drives are high quality metal USB3.0, so if you save the files to your PC hard disk, the USB Flash Drives can be used over and over! Want to know more? Full details at siliconchip.com.au/shop/digital_ pdfs siliconchip.com.au Australia’s electronics magazine March 2021  91