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Keeping the Internet Up By Nicholas Vinen This simple device for the home or office will automatically restart your modem or router if it stops working. It can’t stop your internet connection from dropping out, but it will save you the hassle of pulling the power to see if it’s the router at fault (which is often the case, unfortunately). I t is a sad fact that many of the routers used for NBN connections these days are not terribly reliable. They might work OK for a few days or weeks, then will suddenly quit for no apparent reason. Power cycling them will usually restore your internet connection, which can be annoying if you are not home, but other family members are. Or if it’s in a remote unoccupied office that you have lost your connection to. Ask me how I know! This device is based on the WebMite, with Geoff Graham’s MMBasic software running on a low-cost Raspberry Pi Pico W with built-in WiFi (August 2023 issue; siliconchip.au/ Article/15897). The MMBasic code periodically tries to make a connection to a remote server that you can expect to be operating most of the time (eg, Google, Apple, Microsoft etc). It will try several of those, and if it can’t connect to any, it will briefly interrupt the DC or AC power to your Modem Watchdog Kit SC6827 ($35 + postage): contains all the required (non-optional) items listed (12V relay). You just need a small enclosure to house it. 68 Silicon Chip router to restart it. It will then wait a little while and resume operation; hopefully, after that, it will be able to connect and continue monitoring the connection until it stops working again. It’s built on a small circuit board using only a dozen or so components. To keep it safe and simple, it is connected between the router’s power supply and the router, and it is powered from that same power supply. It will work with modems/routers powered with 9-24V DC or 6-15V AC and it only draws about 50mA extra from that supply. Circuit details The Watchdog circuit is shown in Fig.1. As most of the hard work is done by software running on the WebMite (Pico W), there isn’t much to it. AC or DC from the router’s supply comes in via CON1 or CON2 and is fed to header CON3 via the normally-­ closed contacts of relay RLY1. So most of the time, power is fed straight through to the router. RLY1 is activated for a few seconds when the router needs to be rebooted, briefly cutting its power. When RLY1 is released, the router starts back up and reconnects. Australia's electronics magazine RLY1 is controlled by the Pico W (MOD1) via NPN transistor Q1. When the Pico W’s GP22 digital output is floating or low, Q1 is off and so is RLY1. When the Pico brings that pin high, Q1’s base-emitter junction is forward-biased, and it sinks current from the negative end of the coil, energising it. The 470W resistor limits the base current to the required level; (3.3V – 0.7V) ÷ 470W = 5.5mA, so when multiplied by the transistor’s gain, it can sink around 100mA, more than enough for most typical 12V relays. Diode D2 prevents the coil’s negative end from flying above 12.7V when it switches off, which could damage transistor Q1. The positive end of the relay coil connects to the main DC supply rail via resistor R2. This can be a 0W link when that rail is close to 12V DC, or a 1W resistor with a value chosen to drop the voltage seen by the coil to 12V if the supply rail is higher. A 5V coil relay can be used with a suitable series resistor for a lower supply rail; more on choosing its value later. We also included a 4.7kW/1kW divider across the supply rail that feeds the Pico’s GP28 pin, which can be used for voltage measurements. We siliconchip.com.au USB supply feeding back into REG1. The Pico has an onboard 3.3V regulator, so we don’t need to provide it with exactly 5V. Software Fig.1: the main part of the Watchdog is the Pico W module (MOD1), relay RLY1 and NPN transistor Q1. They conspire to reboot the modem or router powered via CON3 when it stops working. Power for both the modem/router and the circuit comes in via CON1 or CON2. It is rectified, filtered and regulated to power MOD1. did this in case it was helpful for the Pico to monitor the plugpack’s output, which would allow something like a ‘brownout protection’ feature to be added. We’ve tested this function but haven’t enabled it by default, as it doesn’t seem that useful. Power output header CON3 can be wired to a suitable plug cut off a defunct plugpack or cable, or made from a new plug soldered to a length of twin lead. The CON1 input is an onboard 2.1mm or 2.5mm inner diameter barrel socket that many plugpacks will plug into, while header CON2 can instead be wired to an offboard socket if that’s easier, or your power supply’s plug does not fit CON1. Power supply To derive power for the Pico W, first, we apply the input from CON1 or CON2 to bridge rectifier BR1, which has a 220µF filter capacitor across its outputs. This will convert AC to DC, or if the input is already DC, it will ensure that a positive voltage is applied across that capacitor regardless of how the supply output plug is wired. For a 6-15V AC input, we can expect around 7-20V DC (6-15V AC × 1.414 – 0.7V × 2) across the 220µF filter siliconchip.com.au capacitor. We’ll get around 1.4V less than the incoming supply voltage for a DC supply, ie, 7.6-22.6V DC for the stated input range of 9-24V DC. 5V linear regulator REG1 is powered from the voltage across the 220µF capacitor with a 10W series dropper resistor and 100nF input bypass/output filter capacitors. The 7805 has a specified maximum input voltage of 35V, so it will easily handle the maximum expected voltage at its input. Its dropout voltage is around 2V at 1A, so it will be in regulation down to 7V. The WebMite is in sleep mode a lot of the time; when it is operating, it draws around 50mA on average. With a 24V DC input, we can expect REG1 to dissipate 880mW ([22.6V – 5V] × 50mA). That’s within the capabilities of a TO-220 package without a heatsink, although the PCB is designed to allow you to attach a small heatsink if you need to. In most cases, the input voltage will be lower, no more than 15V, so most users will not need to add a heatsink. The Pico W is powered from the output of REG1 via diode D1, which allows you to connect the Pico W to the USB port of a computer without the possibility of the computer’s 5V Australia's electronics magazine The software is written in MM-­ Basic, using Geoff Graham’s WebMite firmware to simplify the code. That is especially useful if you want to modify or customise it, as there is lots of documentation available for the WebMite, and it’s easy to alter its code over a USB or WiFi connection. The program is simple. It updates its onboard clock every two minutes using the internet NTP protocol. If your router is not working, that will fail. In that case, it then tries to connect to major web servers (google.com and microsoft.com), although it doesn’t request any data; it is just checking to see if it can connect. If all three attempts fail, it brings the GP22 pin high for five seconds to cut power to the router, then waits five minutes and reboots, to reinstate the WIFI connection, before it starts monitoring the internet connection again. The watchdog timer is also enabled so that, should something go wrong and the Pico W freezes for too long (at least six minutes), it will automatically reboot. Programming the Pico W You can do this before building the unit. It can be programmed before or after; it doesn’t make much difference, but it’s a little bit easier dealing with the Pico W before it has been soldered to our board. Use a micro Type-B USB cable to connect it to your computer and a virtual flash drive should be detected. You can either load MMBasic onto it, making it a WebMite, then install the BASIC code and set it up yourself, or load our “RouterWatchdogV1.uf2” The Modem Watchdog shown at actual size with the PicoW unplugged. November 2023  69 Replace ssid and password with your WiFi network credentials. After typing that command and pressing Enter, the Pico W will reboot and attempt to connect to your WiFi network. You can verify this has worked by reconnecting to the USB serial port, pressing CTRL+C again and typing: PRINT MM.INFO(IP ADDRESS) This should give you an address like 192.168.1.100, indicating that it is connected to your network, which means the device is now working. You can unplug it and proceed with construction. Component selection The assembled board, ready to be mounted in a small plastic case. file, which already has the BASIC code loaded and most of the settings configured. You can download that file from our website at siliconchip.com.au/ Shop/6/260 See the panel on loading the BASIC code and setting the options if you’d prefer to do that yourself. There are a few settings we can’t provide, like the WiFi network credentials, so once the firmware is loaded, you’ll need to open a serial connection to the WebMite to finish the setup. You can use a free program like PuTTY or Tera Term to connect to the WebMite’s virtual serial port at 115,200 baud. Press CTRL+C, and after a while, you should see the “>” prompt (be patient, as it won’t respond to key presses in sleep). Enter the following command: OPTION WIFI “ssid”, “password” 100nF CON2 REG1 VERIFY POLARITY CONSISTENCY COIL 100nF ~ – + ~ COIL 40 30 + ~ – + ~ MOD1 1 38 37 39 36 2 35 3 5 4 34 31 33 7 8 32 6 9 11 28 29 10 12 26 27 13 25 14 16 23 24 15 18 17 21 22 40 38 Silicon Chip Q1 CON3 ALTERNATIVES CON1 D2 Fig.2: the missing parts are for optional features. See the “Component selection” section of the article to calculate the value for R2 and select an appropriate relay. 70 19 20 1 2 37 39 36 R2 The Watchdog PCB layout is shown in Fig.2. Some components may depend on your router’s power supply voltage or are for features that aren’t required for the basic function, so those components are shown translucent, with their values in parentheses. Start by mounting the axial components, such as resistors and diodes; the diodes must be orientated with the cathode stripes facing as shown. Fit the bridge rectifier next, ensuring its + symbol is in the location shown, then the transistor with its flat face towards the top of the board. Now fit the two smaller capacitors, followed by the DC socket; try to make the latter parallel/perpendicular to the PCB edge before soldering it. Then you can install the two polarised headers, the electrolytic capacitor D1 10W B R1 RLY1 3 5 CON1 4 33 220mF 35 470W 34 31 + 32 28 30 Q1 29 CON2 26 CON3 27 23 25 24 21 22 (1kW) Construction MICRO USB–B PORT RASPBERRY PI Pico W SWDIO (4.7kW) 7 8 GN D 6 9 10 13 12 11 14 15 16 18 17 19 20 RP2040 MCU WIFI SWCLK MODULE The only components you may need to change are the relay (RLY1) and its coil’s series resistor (R2). Start by using a DVM to check the output voltage of the plugpack powering your modem or router. Determine whether it is AC or DC and its magnitude. If it’s 12-15V DC or 9-12V AC, you should be able to build the unit as per Figs.1 & 2 and the parts list, with R2 replaced with a wire link. If it’s above 12V DC but below 24V DC, or above 10V AC, use a 1W resistor for R2. For a DC supply with a voltage of Vin, its ideal value is (Vin − 13.4V) ÷ 0.044A. That’s based on the 44mA coil current for the JW1FSN-DC12V relay specified. For example, if the supply is 18V DC, you would use 104.5W ([18V − 13.4V] ÷ 0.044A), which we can round to 100W. For an AC supply above 12V (Vacin), multiply the voltage reading by 1.414, then plug the result into the formula above. For example, for 12V AC, 12V AC × 1.414 = 17V DC, which gives us a value of 81.8W, close to the preferred value of 82W. If your supply is close to 24V DC, you could go back to using a wire link for R2 and substitute a 24V DC coil relay for RLY2. For supplies below 12V DC or 9V AC, use a 5V DC coil relay for RLY1 with a series resistor. The formula for that resistor value is (Vin − 6.4V) ÷ 0.106A; if it’s an AC supply, again multiply the voltage by 1.414 first. For example, for a 9V DC supply, use a 5V relay with a series resistor value of 24.5W ([9V − 6.4V] ÷ 0.106A), which we can round to 22W or 24W. Similarly, for 6V AC, use 19.7W ([6V × 1.414 − 6.4V] ÷ 0.106A), so select either 18W or 22W. Fig.3: the only wiring strictly required is for the output cable that goes to the modem/router, as shown here. An external power input connector can be wired into CON2 if the onboard connector doesn’t suit your modem/router’s power supply. The polarity only matters because it must be consistent between the input socket and output plug if using a DC supply. Australia's electronics magazine siliconchip.com.au and the regulator. The electro has its longer (positive) lead towards the top of the board and the stripe on the can, indicating the negative side, towards the bottom. The regulator shouldn’t need a heatsink but its tab is near the edge of the board, so you can fit one if you want to. There are a few different ways to mount the Pico W. You can mount it horizontally or vertically; either way, you have three ways to solder it: solder the two boards directly to each other, use a header to join them, or use a header and socket, allowing you to easily unplug the Pico W. In our prototype, we mounted it horizontally into a socket so we could unplug the Pico W during development if necessary. However, it’s much easier to solder it directly using a header (straight or right angle), depending on what will fit in your box best. Therefore, the kit will include headers but no socket. Before soldering it, check if it will block access to two of the PCB mounting holes. If so, you’ll have to attach spacers to them first, and you might want to use Nylon screws to ensure they can’t short against the Pico W. We’ll leave the choice to constructors, but regardless of your method, check that you’re connecting it the right way around. Only half the pins of the Pico are soldered to the board, with pin 21 on the connector end of our board and pin 40 at the regulator end. If in doubt, check Fig.2. If mounting it horizontally, it will hang off the edge of our board. Finally, fit the relay. It will only go in one way. Ensure it is pushed down fully before soldering its pins. Then attach tapped spacers to the corners of the board using machine screws. Wiring For the power supply cable to the router, you will need a length of twin lead with a suitable socket on the end, as shown in Fig.3. We will supply a USB-to-barrel-socket cable in the kit, with the reasonably common 2.1mm inner diameter plug type. It will suit many routers but probably not all. The idea is to cut off the USB plug and crimp and/or solder it to a polarised header plug, then plug that into the output header, CON3. If the supplied cable is no good, you’ll need to find or make one with the correct plug for your router. siliconchip.com.au Parts List – Modem/Router Watchdog 1 double-sided PCB coded 10111231, 51 × 42mm 1 Raspberry Pi Pico W microcontroller module (MOD1) 1 12V DC coil 5A+ SPDT relay (RLY1) ● [Jaycar SY4050, Altronics S4197 or JW1FSN-DC12V] 1 PCB-mounting barrel socket, 2.1mm or 2.5mm inner diameter (CON1) 2 2-way vertical polarised headers with matching plugs (CON2, CON3) 1 20-way straight or right-angle header (for mounting the Pico W) 1 20-way female header socket (optional; to socket the Pico W) 1 barrel plug and cable from a disused plugpack or USB to barrel plug cable 8 M3 × 6mm panhead machine screws 4 10mm long M3-tapped spacers Semiconductors 1 7805 5V 1A linear regulator, TO-220 (REG1) 1 BC547 100mA 45V NPN transistor (Q1) 1 W02M/W04M/2W02/2W04 bridge rectifier (BR1) 2 1N4004 400V 1A diodes (D1, D2) Capacitors 1 220μF 50V electrolytic 2 100nF 50V ceramic or MKT Resistors (all 5% unless noted) 1 470W ¼W 1 10W 1W 1 1W 5% resistor (value depends on supply voltage and relay used; see text) ● a 5V or 24V relay might be required if the router power supply is unusually low or high MMBasic Code Listing WATCHDOG 65000 PRINT “Watchdog initialising” SETPIN GP22, DOUT PIN(GP22) = 0 SETPIN GP28, AIN ON ERROR IGNORE CPU SLEEP 60 DO WATCHDOG 65000 CPU SLEEP 60 WATCHDOG 200000 PRINT “Checking NTP” WEB NTP -10 IF MM.ERRNO THEN PRINT “Checking Google” WEB OPEN TCP CLIENT “google.com”, 80 IF MM.ERRNO THEN PRINT “Checking Microsoft” WEB OPEN TCP CLIENT “microsoft.com”, 80 IF MM.ERRNO THEN PRINT “Rebooting router” PIN(22) = 1 WATCHDOG 10000 CPU SLEEP 5 PIN(22) = 0 WATCHDOG 200000 CPU SLEEP 180 CPU RESTART ELSE PRINT “OK” WEB CLOSE TCP CLIENT ENDIF ELSE PRINT “OK” WEB CLOSE TCP CLIENT ENDIF ELSE PRINT “OK” ENDIF WATCHDOG 65000 CPU SLEEP 60 Australia's electronics magazine LOOP November 2023  71 Silicon Chip Binders REAL VALUE AT $21.50* PLUS P&P Are your copies of Silicon Chip getting damaged or dog-eared just lying around in a cupboard or on a shelf? Can you quickly find a particular issue that you need to refer to? Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of S ilicon C hip . They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. H 80mm internal width H Silicon Chip logo printed in goldcoloured lettering on spine & cover Silicon Chip Publications PO Box 194 Matraville NSW 2036 Order online from www. siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *see website for delivery prices. 72 Silicon Chip It doesn’t matter which way you wire it to header CON3, except that it needs to be consistent with the input connection to CON1 or CON2. To check this, ensure the output is not connected to anything and plug the power supply into CON1 or CON2. Use a DMM to check for continuity between the outer barrel of the power supply’s plug and the outer barrel of the plug that will go to the router. If not, swap the connections at CON3, then check again. We don’t want to reverse the polarity of the power applied to the router (although that won’t matter if it’s low-voltage AC). It’s a good idea to double-check this by plugging the power supply into a mains GPO and using a digital voltmeter to check the polarity of the Watchdog’s output plug. Make a note of whether the inside of the socket is positive or negative relative to the outside, then unplug the supply from the unit and verify that its output polarity is the same as what you measured coming out of the Watchdog. You can also check the sticker on the back of your router to verify it’s expecting the same polarity. Housing it The board is unfortunately too large to easily fit into the smallest Jiffy box (UB5), although it will fit comfortably into the next larger one (UB3). You could put it in just about any enclosure, or even use it as a bare board, as long as you’re careful that it can’t short against anything! If the onboard barrel socket doesn’t suit your router power supply, you will probably have to put it in an enclosure so you can wire up an appropriate chassis-­mounting socket via CON2. Testing Connect the output power plug to your router, along with all the other cables the router needs to operate. Power the whole thing up and check that the router lights come on and your internet connection is working after a few minutes. Leave it for 15 minutes to verify that the Watchdog relay does not trigger, causing your router to reboot. If it does, it probably can’t connect to your WiFi network, so connect the Pico W back to your computer and correct the WiFi credentials. Assuming it’s working, disconnect the internet cable from your router (from the NBN box or whatever is upstream). Wait a few minutes; you should hear the Watchdog relay click, and the router will reboot. Plug the internet cable back in, as it is all working as expected. If that doesn’t happen, you might not have loaded the firmware correctly. If you can’t figure out what has gone wrong, you might need to load the Pico W firmware again from scratch. That involves holding the white button down on the Pico W while plugging it into your computer via a USB cable so that the virtual flash drive SC appears again. Loading the firmware manually Start by loading the WebMite firmware onto the Pico W. You can refer to the August 2023 article on the WebMite (siliconchip.au/Article/15897). However, the procedure is basically the same as mentioned in the article; you just load the WebMite .uf2 file rather than the one specific to this project. It is also available to download from our website (siliconchip.au/Shop/6/230). The next step is to connect to the WebMite using the USB virtual serial port (as described in the article text), then load the BASIC code and set up the options. The BASIC file is called “ModemWatchdog.bas” and is part of the download package linked in the article text. Open the BASIC file in a text editor like Windows Notepad. Connect to the WebMite using Tera Term or PuTTY, then in Notepad, press CTRL+A (to select the whole program) and CTRL+C (to copy it). If using PuTTY, right-click in the windows to paste the program, then press CTRL+Z. If using Tera Term, go to that window, press CTRL+V (or ALT+V) to paste the program, then press CTRL+Z. You should be back at the MMBasic prompt with the code loaded. You can check it has been loaded by running the LIST command. Now set up the options as below. Note that you’ll probably need to reconnect to the WebMite between some of them: OPTION WIFI “ssid”, “password” OPTION TELNET CONSOLE ON OPTION AUTORUN ON Australia's electronics magazine siliconchip.com.au