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Image source: https://unsplash.com/photos/water-droplets-on-a-window-with-blurred-green-plants-Fr4as0DLD4E Human Comfort Indicator Whether it’s a couch or the environment, comfort is often subjective. That is true of temperature, too; you will feel a lot less comfortable on a warm day if the humidity is high. Thus, this Human Comfort Indicator is much more useful than a mere thermometer because it tells you how hot it feels. By Tim Blythman T his project comes about due to a request from a magazine contributor. He said it would be handy to have a device that shows whether an environment is comfortable or not, not just the raw ambient temperature. While comfort is subjective, this device deals with parameters that can be easily measured and quantified. It is well known that certain combinations of temperature and humidity can be uncomfortable to humans. Naturally, this can also apply to animals and plants. You would have no trouble identifying conditions that feel uncomfortable for yourself, but it’s handy to be able to put a number on it, so you can be alerted when others might not be comfortable. One suggestion we heard is that the Human Comfort Indicator would be well-suited to monitoring the conditions in a greenhouse. Comfort and dew point The parameter we are tracking with the Human Comfort Indicator or HCI is the ‘dew point’. This is the temperature to which air must be cooled for liquid water to start condensing from it. Being a temperature, it is measured in °C or °F, but it relates to both the raw temperature and the relative or absolute humidity. Let’s look at some theory to explain why dew point is important. If you are in a warm environment that makes you perspire, the dew point has come into play. As the perspiration (sweat) evaporates, it cools your skin, Features Displays temperature, humidity and dew point Historical displays for the last day, week and month Configurable units, display orientation and update frequency Battery-powered with USB charging for uninterrupted operation The ultra-low-power e-paper display is unobtrusive and easy to read at a distance Optional analog (voltage) dew point output Open-drain alarm output Specifications Displays temperature/dew point in °C or °F to the nearest degree Relative humidity shown to nearest % Based on the excellent BME280 sensor Average battery draw of around 300μA gives months of operation on a single charge Screen update interval: every five minutes siliconchip.com.au Australia's electronics magazine but it cannot cool any lower than the dew point, since that is the temperature at which the air is saturated with water. In this case, ‘saturated’ is used in the scientific sense; it means that the air is at 100% relative humidity. Intuitively, as the dew point approaches the ambient temperature (due to the dew point rising or the ambient temperature falling), the relative humidity rises. This can be an indicator of changing weather conditions such as rain. You might see some weather forecasts report a ‘feels like’ temperature. This takes into account the dew point, as well as factors like wind and sun. For indoor conditions, the sensation will be dominated by the dew point. At very low dew points, evaporation from the skin increases, which can cause problems like skin drying out and cracking. Important, this is not necessarily something you would notice, unlike high humidity. So it’s handy to have a device that can alert you to this condition, allowing you to do something like switch on a humidifier. Table 1 shows some typical ranges of interest for dew point. It can be quite subjective; if you live in a tropical area, you may be comfortable at ranges higher than those suggested. Measurements Dew point sensors are not common, but a figure can be easily derived if June 2026  43 the relative humidity and temperature are known. Thankfully, many modern sensor modules can read both. Historically, an arrangement known as a wet-bulb thermometer would be used. This is a glass thermometer that has its bulb surrounded by a piece of cloth soaked in water. The water evaporates, cooling the bulb and reducing the indicated temperature below ambient. It would often be used in conjunction with a drybulb thermometer to give the true air temperature. The ‘sling psychrometer’ is a device fitted with a wet-bulb and dry-bulb thermometer. It is spun around above one’s head for a minute or so, quickly bringing the wet-bulb thermometer to equilibrium. A chart was then used to determine the dew point from the two temperatures. Thankfully, you don’t need to swing the HCI around above your head! The equations for converting temperature and relative humidity to dew point are complex but well-­ established, so it is a simple case of performing readings from our sensors and then a few calculations to produce the desired figures. Design As you can see from the photos, the Human Comfort Indicator has a simple design that would suit being used around the home, similarly to a weather station. The case is 3D-printed, although the PCB is designed to be easily mounted inside any suitable enclosure with a few holes in it. Table 1: Dew point interpretation Dew point Subjective condition <5°C Very dry 5-10°C Dry 10-15°C Comfortable 15-20°C Mostly comfortable 20-25°C Muggy >25°C Uncomfortable Original source: https://media.bom.gov.au/social/ blog/1324/feeling-hot-and-bothered-its-not-thehumidity-its-the-dew-point/ We use an e-paper panel to display the readings. These draw close to zero power except when they are actually updating, so they are a good choice for a battery-powered device. They are also easy to read under a wide range of light conditions as they are similar to ink on paper. We have written a feature article with more details on e-paper in this issue. It includes some background on the technology and how we came to choose a specific panel. The person who suggested this project also asked for some extra outputs on the device. The first is an analog voltage that reflects the dew point temperature, which can be used as an input to another system, such as a data logger. The other is an open-drain output that can be triggered when certain conditions are met, such as the temperature or dew point falling outside preset ranges. It is controlled by a small Mosfet capable of sinking a few hundred milliamperes, so it can After the SMD parts have been fitted and the micro has been programmed, you can test the e-paper panel by supplying power via the USB socket. You will see this error message since the sensor has not been fitted. 44 Silicon Chip Australia's electronics magazine directly drive a buzzer or even a small relay if a larger load needs to be controlled. Circuit details Fig.1 shows the circuit diagram of the Human Comfort Indicator. The circuitry around CON4 and the MOD2 e-paper panel is virtually identical to that described in the feature article. It differs from the breakout boards we tested mainly in using larger components to simplify soldering. This part of the circuit generates the necessary voltages to drive the display panel. Mosfet Q1 is driven by the display controller on the e-paper panel to provide ±20V rails. BS1 is tied low to force the controller into 8-bit SPI mode. The circuit is driven by a 16-bit PIC24FJ256GA702 microcontroller (IC1) boasting 256kiB of flash memory and 16kiB of RAM. The large amount of flash allows us to store graphics, such as font data, while the RAM allows us to create a buffer large enough to store an entire screenful for display, something that would not be possible with most 8-bit microcontrollers. We’ve established that the PIC24­ FJ256GA702 is capable of low-power operation, having used it in the ESR Tweezers project from the June 2024 issue (siliconchip.au/Article/16289). It also has hardware multiply and divide functions, which will help performing the mathematical operations needed to process our readings. On top of all that, it’s relatively inexpensive. IC1 is supplied from the 3.3V rail and also has two 100nF supply rail bypass capacitors plus the necessary 10μF capacitor on its VCAP pin (pin 20). This bypasses an internal regulator used to power the processor core at between 1.2V and 1.8V. Pins 1, 4 and 5 are ICSP (in-circuit serial programming) pins connected to CON1, along with 3.3V and ground, allowing it to be reflashed after soldering. Pin 1 has a 10kW pullup resistor to allow normal operation unless a programmer is connected. IC1 controls the e-paper panel via six lines: three for the SPI interface and three more control signals. The PPS (peripheral pin select) feature of IC1 allows most peripherals (like the hardware SPI interface) to be directed to most pins, simplifying the PCB layout. One exception is the Vout signal, siliconchip.com.au Fig.1: the circuitry around Q1 and connecting to the e-paper display via CON4 is driven by the controller on the e-paper panel. These components generate the various supply rails needed to drive the display. Our feature article in this issue (see page 66) covers this in more detail. which is provided by the analog CVref peripheral, which is fixed at pin 25. The CVref output comes from a 5-bit DAC. When using the 3.3V supply rails as its inputs, we get 32 steps over 3.3V, or near enough to 0.1V resolution for the Vout signal. This is simply made available, along with a ground connection, at pin header CON5. The opendrain output is provided at CON6, is implemented using Mosfet Q2, driven from pin 11 of IC1. A bi-colour LED, LED2, is driven from another two I/O pins via a 1kW series resistor. The two pins allow it to be lit up red or green, or off entirely. Three tactile pushbutton switches are connected to three more I/O pins on IC1. These are configured as inputs with internal pull-up siliconchip.com.au currents, allowing the switch states to be detected. Each pin is pulled to ground by the associated switch when it’s closed, or held high by the pull-up current the rest of the time. The last component is sensor module MOD2, which is connected at CON3, a six-way header to suit its pinout. This module includes a Bosch Sensortec BME280 humidity, pressure and temperature sensor. We have chosen it because it contains only the bare minimum circuitry needed to operate the sensor chip. Specifically, it lacks a voltage regulator, so we don’t need to worry about a poorly designed module wasting power in an inefficient regulator. The sensor IC itself is designed for 3.3V operation, so it can run from the Australia's electronics magazine same rail as the microcontroller. It consumes just 0.1μA in sleep mode. The chip and module can work in either SPI or I2C mode; we are using I2C in this case. The module includes bypass capacitors and pullup resistors for the communication lines. It is an updated version of the GY-BM module described in our review of Pressure/Temperature Modules (December 2017; siliconchip. au/Article/10910). The similar circuit of that module is shown on p82 of that article. Power supply Like the e-paper controller, IC1 is a nominally 3.3V device (3.6V maximum), so the main logic and supply voltage is set at 3.3V. This comes June 2026  45 from REG1, an MCP1700-3302 LDO (low dropout) regulator. Helpfully, it also has a low quiescent current of around 2μA. This is in turn fed from one of two sources by a common-cathode dual schottky diode, D1. One anode connects to a Li-ion battery, while the other is a 5V supply from USB-C socket CON2. CON2’s CC1 and CC2 pins are connected to the requisite 5.1kW resistors to ground. These indicate that the device should be treated as a sink and be supplied with 5V when connected to a source. Two alternative locations are provided for CON2 so that the PCB can be constructed to suit one of two particular orientations. 5V from CON2 also supplies the charging circuitry based on IC2. The 10kW resistor sets the charging current to 100mA, the minimum permitted by this chip, while LED1 is another bi-colour LED that shows red while charging is occurring and the STAT pin is low. When charging completes, the STAT pin goes high and LED1’s green element lights. The arrangement of the two 1kW resistors allows this to work. While it might appear inefficient to have the resistors connected across the supply, they will only draw current while 5V is present at the USB socket and won’t drain the battery. The diode arrangement means that there is no current draw from the battery while charging is occurring, so the battery can charge fully. Software Software operation is focused on minimising power consumption where possible. This mostly consists of setting the external modules to low-power modes. The BME280 is checked every 5 minutes and the screen is updated at the same rate. A low-power RC oscillator (LPRC) in the microcontroller keeping time means that the processor can spend much of its time sleeping. The LPRC is configured to provide an interrupt at around 5Hz, quick enough that it can provide timing down to one second with reasonable consistency. Several counters are updated with this interrupt. Some counters keep rough track of hours, days and weeks, allowing daily, weekly and monthly averages to be accumulated. Another counter sets LED2 to light up for about one second every minute; it consumes a few milliamperes when on, so operating it with a low duty cycle reduces the average current consumption. The colour that LED2 shows when lit matches the alarm state; if red, then the alarm is active, Q2 is on and the ALARM output is pulled to GND. Otherwise, LED2 is green and Q2 is off. The sensor readings require a bit of processing. There are a total 18 Scope 1: the idle current of the Human Comfort indicator is around 100μA, with a peak below 5mA (during a full refresh, shown here). 46 Silicon Chip calibration parameters that are unique to each chip; they are used for compensating the raw 16-bit humidity readings and 20-bit temperature and pressure readings. The humidity and pressure readings are further compensated based on the measured temperature. Fortunately, Bosch Sensortec provides sample code to do this. The results are displayed according to user preferences, such as temperature display units. There is also a menu system that allows the preferences and settings to be changed. Since the e-paper display takes so long to refresh, we have kept the options and thus the menus fairly simple to prevent them from being unwieldy to use. We’ll explain more about the operation once construction is complete. Power Scopes 1 & 2 show typical current consumption. Scope 1 shows a full refresh occurring on the main page, with the low levels on each side of the peak representative of the normal idle state below 100μA. The refresh is no more than 5mA for no more than five seconds and occurs about once every five minutes, giving an average contribution of less than 83μA. Scope 2 shows a partial refresh occurring upon entry to the setting screen. Note that the current peak Scope 2: a partial screen refresh requires less current. The 1.5mA draw seen here is due to LED2 being lit while the settings screens are active. Australia's electronics magazine siliconchip.com.au Fig.2: we designed this 3D-printed case (above) to suit the Human Comfort Indicator. It comes in two variants, with this render showing the landscape version, with the USB socket coming out the side. Vents allow the sensor to sample room air. The portrait version is shown in the adjacent photos. is slightly lower due to the partial refresh. The higher level on the right is due to the LED2 lighting up and consuming 1.5mA. During normal operation, the LED is on for approximately one second per minute, contributing an average of 25μA. So we expect the long-term average consumption of the Human Comfort Indicator to be around 210μA. Given that the self-discharge of Li-ion cells is typically around 2% per month, a typical cell will lose 40mAh per month or around 53μA; a significant chunk of the usage! We have quoted 300μA to take into account some time spent on the settings or viewing different pages. With a nominal 2000mAh lithium cell, this equates to 6600 hours or around nine months of operation on battery power. Considerations Since the e-paper display panel includes look-up table (LUT) options for both full and fast refreshes, we have included an option to set how the refreshes occur. Broadly speaking, the full refresh will use more power, but will provide a clearer display. The fast refresh appears less distracting when it happens, but the resulting display has slightly poorer contrast. The above calculations assume that full refreshes occur at all times, so using partial refreshes should provide even longer operation than quoted. The outputs at CON5 and CON6 are nothing more than pin headers, siliconchip.com.au since we expect they may not be used in most cases. The analog output on CON5 is a voltage (in volts) that is one tenth of the dew point (in degrees). So a dew point of 16°C will result in an output of 1.6V; naturally, this is capped between 0V and around 3.1V, the upper limit of the CVref peripheral. It is not buffered and has an estimated output impedance of around 30kW. Unless you are connecting it to a high-impedance input, you may need to buffer it. We have chosen not to provide a buffer, since it would draw extra power that would be wasted if this output is unused. E-paper’s ability to show a display while using no power also has a subtle downside in that it can be hard to tell if the device is working or frozen. The main way we show the health of the Human Comfort Indicator is through the flashing of LED2. If you don’t see LED2 flash occasionally, the Human Comfort Indicator may have shut down due to a flat battery. The voltage of the regulated 3.3V line is also shown on the main page. If this gets near 3.0V, the battery may be overdischarged. There is no built-in overdischarge protection, so a protected cell must be used. That will prevent significant cell damage if you forget to recharge it. Any unit like the Human Comfort Indicator that measures ambient temperature is at risk of being affected by self-heating, where the heat dissipated by the unit’s own operation drives up the measured temperature. Australia's electronics magazine Thankfully, it has very low power consumption, and most of its power consumption occurs immediately after a reading has been taken (when the display is refreshed with the updated readings). So that should not be a probably, provided that the chosen enclosure does not trap heat. Enclosure We have designed a 3D-printed enclosure to suit the Human Comfort Indicator with a vent to allow air exchange. That should not only eliminate self-heating concerns, but it’s also necessary so that the humidity sensor (and to a lesser extent, temperature sensor) can respond to the ambient conditions properly. It will probably take a few hours to print, so we recommend that you start that while assembling the PCB. The two parts simply snap together, and they are designed to be printed without supports. There are two variants of the case, one to suit each position for the USB connector, CON2. One variant suits a portrait layout, with the hole for the USB socket on the long side. The other variant suits a landscape display and has the USB socket on the short side. Make sure that you choose two matching halves before printing them. The render in Fig.2 shows the two halves of the landscape version. We printed our prototypes on an Ender-3 V3-SE and, to ensure the best appearance, used a 0.08mm layer height and low speed, about 50% of June 2026  47 Fig.3: all the SMD parts are on one side of the PCB, with many of the through-hole parts mounted on the back. Try to keep the area under the e-paper panel clear on the back of the PCB. The entire Human Comfort Indicator is just under 9cm tall. It is fully self-contained and is powered from a rechargeable battery that should last close to a year between charges. normal speed. The job took about six hours in total: two hours for the front and four hours for the back half. The result should be usable with minimal post-processing. At most, you might need to remove small burrs or file down the parts if they have been heavily over-extruded. The bezels on the front half of the case (where the display mounts) are quite thin, so take care when removing them from your print bed. The vent holes are nominally 2mm in diameter if you wish to clean them up with a drill bit. The PCB also has mounting holes, allowing it to be fitted to just about any enclosure that is large enough and can have suitable holes made (see Fig.4). The PCB simply mounts to the front panel of such an enclosure using screws and spacers. A UB3 Jiffy box should be a good fit. The view shown in Fig.4 is from the outside of the enclosure. If you are using such an enclosure, we suggest using the bare PCB as a template for the mounting and switch holes. The USB socket will probably not align with the edge of the case, so you will likely have to cut a hole to allow a cable to pass through the case. Options The charging components are inside a white box printed on the PCB. Leaving these parts off will disable the charging feature. You could do this if you don’t want to use an internal 48 Silicon Chip battery; in this case, it will only operate when powered from CON2. We’ll describe the assembly including all components. Simply leave off the battery, battery holder and all parts in that box if you wish to pursue this option. You can also see this outline in the overlay diagram (Fig.3). We recommend using the battery, since this will allow the Human Comfort Indicator to operate during brief power interruptions. Importantly, it will be able to retain its long-term average readings in RAM. PCB assembly There are a few fine-pitch devices on the board, so you will probably need a magnifier and good lighting as well as the usual SMD gear such as flux paste, tweezers and solder-wicking braid. Start by fitting the SMD components, which are all on one side of the PCB. IC1 and CON4 have the finest lead pitches. Apply flux to the pads and rest these components in place, adding more flux on top of the leads. Carefully align the pins to their pads, then check they are correctly orientated before tacking one or two pins in place, making sure that they are flat against the PCB. We’ve made the pads quite long, so you can try applying the iron to the pad only; this should be sufficient to cause the solder to run onto the lead and form a proper joint. Check for any bridges and use the braid to remove Australia's electronics magazine excess solder, adding more flux as needed. When you are sure that CON4 is properly soldered, apply a solid fillet to each of the larger end pads for mechanical strength. Next, solder IC2. It has five pins, so it will only fit properly in one orientation. Follow with the three-lead SOT23 parts. Note that this includes a regulator, two Mosfets and a dual diode, which all look similar, so don’t get them mixed up. There are also three single diodes to be installed; solder them next, making sure to place the cathode stripes near the K symbols, as shown in Fig.3. Follow with the capacitors; they will not be individually marked. The 1μF parts are the most numerous, so we recommend starting with these. Ten are at the lower left near CON4, while two are near REG1. Most of the 1μF parts are in a single row that also includes a solitary 100nF capacitor, so watch out for the interloper. Two of the 10μF capacitors are near IC2, with the third near IC1. These will probably be thicker than the other capacitors, so you might be able to tell them apart. Follow with the single 4.7μF capacitor (or 10μF as supplied in the kit) and the two remaining 100nF capacitors, near IC1 and the interloper in the row of 1μF parts. The solitary inductor has large pads, but it doesn’t have a huge thermal mass, so soldering it should be straightforward; it is not polarised. siliconchip.com.au Follow with the 11 resistors, checking their markings (1003 or 104 = 100kW etc). To complete the SMD parts, fit CON2 to your preferred location. Be sure to add solid solder fillets to CON2 so that it is mechanically secure. That completes the SMD components, so clean up the residual flux with a suitable solvent and check for any bridges or dry solder joints. If you need to reflow any joints, repeat the cleaning process in that area. When finished, allow the board to dry. You can perform a brief check by applying USB power to CON2. You should see 3.2-3.4V on the second pad of CON1 relative to ground. Ground is the middle pad of CON2, or the marked pads on CON5 or CON6. If you do not see this voltage, disconnect power immediately and investigate before proceeding. Programming IC1 If you purchased the chip from the Silicon Chip Online Shop, it will be programmed and you can skip to the next step. Otherwise, fit a vertical pin header to CON1. The reverse of the PCB is where the e-paper module will sit, so it is best to minimise the amount by which components protrude into this area. Inside our 3D printed enclosure, the display panel sits 1.5mm from the PCB, so this is the absolute maximum by which items should extend behind the PCB in this area. One way to do this is to mount the header with its plastic block sitting off the PCB slightly. There should be enough clearance so that CON1 can be left in place afterwards. Connect your programmer to CON1; a Snap, PICkit 4, PICkit 5 or PICkit BASIC should all be suitable. You can use the CON2 USB socket to provide power. Open the Microchip MPLAB IPE program and use it to program the 2110526A.HEX file into IC1 and verify it. Checking the display Disconnect any power supply before proceeding. You can now check that the display panel is functional by plugging it into CON4. Pull the grey tabs outwards, parallel to the PCB, to release the catch. Slot the FFC (flexible flat cable) into CON4 with the gold contacts facing upwards. The gold part should not be visible when the FFC is fully inserted. Then carefully push the tabs back in. siliconchip.com.au Parts List – Human Comfort Indicator 1 double-sided 50 × 80mm PCB coded 21105261 1 3D-printed case (alternative parts listed at the bottom) [SC7453/SC7684] 1 single AA (14500 size) PCB-mount cell holder 1 Li-ion rechargeable 14500 (AA-sized) cell with built-in protection 1 5-pin header, 2.54mm pitch (CON1; optional, for ICSP) 1 SMD USB-C power-only socket (CON2) [eg, GCT USB-4135-GF-A] 1 6-way right-angle header, 2.54mm pitch (CON3) 1 24-way SMT FFC top-connect ZIF socket (CON4) [EastRising ER-CON24HT-1; www.buydisplay.com/24-pin-0-5mm-pitchtop-contact-zif-connector-fpc-connector] 2 2-way headers, 2.54mm pitch (CON5 & CON6; optional, for external signal connections) 1 47μH 6×6mm SMD inductor (L1) [LSXBD6060WHL470M from DigiKey] 1 3.3V 6-pin BME280 module (MOD1) [Silicon Chip SC5482] 1 EastRising ER-EPD029-2B 2.9in EPD module with 24-pin FFC connector (MOD2) [www.buydisplay.com/serial-2-9-inch-e-paper-screen-128x296for-electronic-shelf-label-lcd] 3 6×6×7mm through-hole tactile switches (~3mm actuators) (S1-S3) 1 piece of foam-backed double-sided tape or similar to secure e-paper panel to main PCB 4 small self-adhesive rubber feet (optional) Semiconductors 1 PIC24FJ256GA702-I/SS microcontroller programmed with 2110526A.HEX, SSOP-28 (IC1) 1 MCP73831T-2ACI/OT Li-ion charge controller IC, SOT-23-5 (IC2) 1 MCP1700-3302E/TT LDO 3.3V linear regulator, SOT-23 (REG1) 2 AO3400 30V 5.8A SMD N-Channel Mosfets, SOT-23 (Q1, Q2) 1 BAT54C 25V 200mA dual common-cathode schottky diode, SOT-23 (D1) 3 MBR0540 50V 0.5A schottky diodes, SOD-123 (D2-D4) 2 3mm bi-colour red/green 2-lead LEDs (LED1, LED2) Capacitors (all SMD M2012/0805 MLCCs) 3 10μF X5R 16V 1 4.7μF or 10μF X5R 16V 12 1μF X5R 50V 3 100nF X7R 50V Resistors (all SMD M2012/0805 ±1% ⅛W) 1 100kW 4 10kW 2 5.1kW 3 1kW 1 0.47W Alternative parts for non-3D-printed case 1 UB3 Jiffy box (see Fig.4 below) 2 M3 × 10mm panhead machine screws 2 M3 hex nuts 2 3mm-long, >3mm inner diameter untapped spacers CL Fig.4: if you don’t plan to use our 3D-printed case design, use this 34.5 34.5 diagram to cut and 22.5 drill a UB3 Jiffy 69 box lid instead. 32 DISPLAY Find the centre of WINDOW your panel by marking where 9.5 the two diagonals cross; this should 2 help to centre 8 12 7.5 5 12 12 Ø3 Ø4 Ø4 Ø4 Ø3 Ø3 the display and controls. Use the blank PCB to mark ALL DIMENSIONS IN MILLIMETRES the panel first. CL Ø3 10 SCALE: 100% SC7646 Kit ($60 + postage): includes everything except the case and battery Table 2: Settings summary Number Setting Options Notes 1 Dew point minimum Alarm on or Alarm off If this is off, the alarm is not triggered by a low dew point 2 Dew point minimum -10°C to 30°C or 14°F to 86°F Increments in steps of the currently selected units 3 Dew point maximum Alarm on or Alarm off If this is off, the alarm is not triggered by a high dew point 4 Dew point maximum -10°C to 30°C or 14°F to 86°F Increments in steps of the currently selected units 5 Sensor fail Alarm on or Alarm off If this is set off, then the alarm is not triggered by sensor failure 6 Units °C or °F All temperature settings and figures are shown in these units 7 Orientation Portrait, Adjust to suit the case or landscape, installation reverse portrait or reverse landscape 8 Text Black text or white text The background is the opposite of the text colour 9 Refresh Always, Hourly Daily This is how often a full refresh occurs; otherwise, a fast refresh happens 10 Flash options S3: Save to flash S2: Restore from backup The “Ready” message will change when a save or restore has completed This board has all the SMDs fitted but none of the through-hole parts (yet). The completed PCB is shown on the left before installation in the case. 50 Silicon Chip Australia's electronics magazine In use, the flexible cable bends 180° to put the display on the back of the main PCB, but for now, the whole assembly can lay flat on your workbench. These panels are quite fragile, so handle with care. Applying USB power at CON2 should cause the display to operate. If it flickers but turns solid black or remains white, it could be that one of the leads for CON4 or one of the components in that area of the PCB is soldered incorrectly. Disconnect the power and remove the display by pulling out the grey tabs, then investigate the fault and rectify it before proceeding. Last components Finish assembling the PCB by soldering the last few components. The three tactile switches and two LEDs should be soldered flat against the PCB. These are all on the opposite side to the previously fitted SMD components. The LEDs should be fitted such that the green cathode (shorter lead) is towards the nearest edge of the PCB. You can easily test this by applying power to the USB socket and carefully connect the LED between pins 1 and 3 of CON1, avoiding contact with pin 2. Whichever pin is connected to pin 3 when the LED lights up is the cathode – see Photo 2. The battery holder should also be on the same side as the SMD components. Trim its leads short so they don’t protrude too far into the area where the display panel will sit, and double-check the polarity. The AAA markings were intended to allow a pair of 1.5V AAA cells to power the Human Comfort Indicator, but we have not tested this configuration, and you should use the AA markings. The last component to solder will be the sensor module, connected via the CON3 header. Ideally, this should be spaced off the PCB as far as possible and near the vents in the rear of the 3D-printed case. Use the right-angle header to achieve this, being sure to maintain clearance from the battery and its holder. You can rest the PCB on the posts in the back half of the base to check the position and clearance. You can test these components similarly to before, by connecting the display panel and USB power. Check that the display updates to show our splash screen with an “OK” message below siliconchip.com.au it. If it says “Sensor error”, it has not been able to communicate with the sensor and you should check the circuitry around CON3. You should see LED2 flash red or green within a minute if all is well. LED1 might flash momentarily, but will probably not show a true indication until the battery is fitted. Completion Now is a good time to add the foambacked tape. We opted to attach some pieces to the PCB and leave the backing sheet on the side facing the display panel. This was still sufficient to hold the panel in place without having to worry about aligning the two permanently. Slot the display panel into the bezel window, with the FFC cable curving around at the notch near the USB socket. Carefully attach the display panel to the PCB and rest the PCB in place above it. The tape should apply just enough pressure to keep the display panel in place. Install the battery and check that the display operates as previously. Snap the back of the case on. You might like to add some small rubber feet to the lower four corners Screen 1: the default main screen shows information in portrait. This design was tested in late February and it is a bit sticky, as the dew point suggests! siliconchip.com.au If a bicolour LED, connected as shown here, lights up then the lead on the middle pad is the cathode (for the green element, in this case). of the case, since it is quite small and light. This should prevent it sliding around when connected to a USB cable. Using it For the most part, the Human Comfort Indicator should be working as intended from power-on. Screen 1 shows a typical display. As noted earlier, the Human Comfort Indicator can also show the daily, weekly, or monthly average statistics. This is done on the main page by pressing S3 or S2. The screen will refresh and show the respective averages if it has recorded enough valid values. Screen 2: one page of settings is for configuring display preferences. The last item allows all settings to be permanently saved to flash memory. If you see dashes displayed instead of numbers, there may not have been enough values recorded to make up the average. As expected, you will not see a monthly average until a month has expired. You might also see dashes if there is a problem with the sensor module. Changing settings Screens 2-5 show the settings and other options. All setting changes are effective immediately. They can also be permanently saved to flash memory, which will mean that those settings are restored after a power cycle. The main choices for the display are the orientation and colour scheme: black text on a white background or vice versa. The portrait and landscape settings should suit the two different 3D printed case variants. You can also choose a reversed (rotated 180°) option if you prefer. Another setting is a choice between °C and °F for temperature displays. Internally, all temperatures are stored as units of 0.01°C and converted where needed. You can also choose whether a full screen refresh occurs every five minutes (always), every hour, or every day (see Screen 2). Screen 3: the other settings page relates to the alarm outputs. Whether the alarm is triggered for a low or a high dew point can be set independently. Australia's electronics magazine Screen 4: the white text on a black background looks striking; it would be very impressive if used with a black 3D-printed case. June 2026  51 Screen 5: the landscape format lays out the main data screen in this fashion; the settings screens put the items into two columns. There are also some alarm settings: the minimum and maximum dew point and whether either threshold is enabled (or neither, or both). You can also set the alarm to trigger if a problem is detected with the sensor. Screen 3 shows these; they are all enabled by default. Because of the slow update rate of the e-paper panel, the settings menus operate slightly differently to those you might have seen in our other projects. Pressing S1 (closest to LED2) enters the settings menus and the alarms are shown first. LED2 is lit solidly while in the settings menus. Each button press is followed by a one-second delay before being acted upon. This allows multiple button presses to occur before the screen is refreshed, so it is easier to make bulk changes. LED2 switches off to indicate that a refresh is pending. Screens 2 and 3 show the cursor marker that indicates which item is being edited – S1 skips to the next option. For numeric values, S3 decrements them and S2 increments them. For binary options, either S2 or S3 will toggle the state. For example, to change the dew point maximum from 20°C to 15°C, you would press S1 once to enter the settings, then allow the screen to refresh. Press S1 three times quickly to jump to the DP maximum setting. Allow the refresh to happen to make sure you are changing the right item. Then press S3 five times to drop the setting by 5°C. Let the refresh occur and check that the value is correct. Then press S1 six times to jump forward to the flash memory options, then press S3 to save and check that you see the “Save done” message. Finally, press S1 to return to the main screen. Table 2 summarises the settings. If the settings appear to be corrupted, you can use Restore (S2) on the last settings item to reload the initial settings from flash memory. You should immediately use S3 to save these to flash memory to be sure that everything is as new. Since LED2 is on for the settings screens, it uses much more power than the main screen. So if 30 seconds elapses without a button being pressed, the Human Comfort Indicator returns to the main screen displaying temperature, humidity and dew point. Summary The Human Comfort Indicator will be a great addition to any household that needs to keep track of the local humidity and dew point. We’re sure readers will find interesting applications for the alarm and analog voltage outputs. The firmware and STL files can be found at www.siliconchip.com. SC au/Shop/6/3630 Back Issues The UK ’s Circui t Pr Electractical onics fT sTa r TE r premier electron ics so and Underst Surgery using anding and gyrato rs Make computin g ma ker ma Mrom Finishin h Mic E Th g gazine light con the PicoMite ite E ‘sP La troller T’ aT Audio softwar smart e Designi Out sw iTc h- on discreteng a practic ! al audio op am a Mi p GPS-Sy Analog nchronise ue Cloc d k it wit Ta 6- d Ec WIN M mTo ICRO A CH u Dev ch AR IP elo 10 adE pm 00 LLionPico r Es Kit ent PrEc MisE VaLU ite smis Ta n c Es Tolight E b ox finECont art YoUr TUnErolle dEsiG r ns WIN! Microch ip Inte grat Graphic ed sE s and Touch M CuriTE osity sT – Pa luation bUEva iLd Kit an rT 3 d Us siL ic E oU on ch r ULTiM Ec kE aT E r Jump start Mini LE Driver D Egg Tim er – eg to pe gcellen rfectio t brea n! kf ast, tim Compl PLUS! APRIL 13 Cover.in dd 1 ractica lelec practic ed etin g WideTechno range the Tal inter Cool Bea k – My tru face, Ohmmet th, you ne r truth techn Net Wo ns – Arduin er and AI o tal t work, cir o Boo rk – Rou k, pic ters, pow tcamp: new n’ mix cuit Surg www.e bo er sup Sep 202 ery, re lectron plies, TEM ards update 3 £5.9 adout, publish 9 ! U and ing.co 09 more m 9 7726 <at>p 32 5730 30 alelec APRIL 201 3 £4.40 tronics Practical Electronics is the UK’s premier electronics, computing & maker magazine. Each month has a wide variety of electronics projects suiting beginners and experts alike. It also includes many different features on topics like audio, radio, computers and more. 14/02/2 013 10:33:4 7 24 YEAR COLLECTION OF PRACTICAL ELECTRONICS Every issue of Practical Electronics published from January 2000 to December 2023. Covering 288 magazines & over 20,000 pages of content; see siliconchip.com.au/Shop/3 PDF Download SC7650 ▸ $165 The articles can be downloaded per month, year or the entire block. Some of the excellent columns of Practical Electronics include Audio Out, Circuit Surgery, Techno Talk and more. The download size is approximately 5.4GB. 52 Silicon Chip PDFs on USB SC7645 ▸ $180 plus postage cost Supplied on a 32GB Silicon Chip branded USB flash drive. Purchasing this also gives you access to the download version shown opposite. Australia's electronics magazine siliconchip.com.au