Connecting test probes to PCBs can be difficult when the contact points are very small, or when you need to keep the probes in place while using your hands to run tests or use a computer. Normal test probes for multimeters, oscilloscopes, and other equipment have to be held in place.
This amazing 3D-printed PCB workstation uses acupuncture needles as test probes. The test probes are attached to adjustable arms that can hold them in position on the device under test.
You can print the plastic parts yourself using the files provided on Thingiverse, or you can buy a kit from the designer. I printed the parts over the space of a few days while I was working on other things. The base takes a few hours to print and there are many other parts, so don’t try to rush through it. Collect everything you need and lay it out to make sure you have it all.
Probe arms: 3D-printed parts, M4 bolt with hex head, washer, and M4 wing nut
Pack of acupuncture needles (I used these ones in 0.35x40mm size)
3D-printed base plate
PCB mounts: 3D-printed bracket, M5 bolt with hex head, washer, and M5 wing nut
light-weight, flexible hook-up wire
Heat-shrink tubing (I used 3mm on the pin headers, and 1.5mm on the needles)
The Thingiverse project includes both large and small PCB holders. I’ve only printed the small ones so far. Thread an M5 bolt up through the base and a bracket, and put an M5 washer and wing-nut on top. Make sure the bracket can slide along the slot.
Stick a rubber foot under each corner of the base, to help it sit securely on your bench and give the bolt heads enough clearance to slide without sticking.
Assemble probe brackets
Insert the vertical bracket into the mounting base. I used a drop of superglue to lock it in place.
Danger! If you put superglue into the mounting base and then squeeze in the vertical bracket, the superglue can squirt out under high pressure. Be very careful that you don’t squirt it into your eyes!
The handles of the acupuncture probes that I bought are about 1.3mm in diameter, and didn’t fit into the mounting clips. I drilled out the clips with a 1.5mm drill, and used super-glue to attach them in place with most of the handle sticking out the top.
The mounting clips are a press-fit into the horizontal arm. Use super-glue to fix them permanently.
Pass an M4 bolt through the vertical mount and horizontal arm, then put an M4 washer and wing-nut on it.
If the end of the acupuncture needle is plain steel, you can solder the wire directly onto it. My acupuncture needles are all stainless steel so I used a ferrule with the plastic cover removed, and crimped the wire onto the end of the needle.
I put 1.5mm heat-shrink tubing over the needle, with just the end exposed. This is optional but it may help prevent the probes from short-circuiting against each other.
Thread the wire along the horizontal arm. What you put on the other end of the wire is up to you: I soldered on a pin header and then put heat-shrink tubing over the joint. Alternatively, you could put on an alligator clip, a banana plug, a spring clip, or whatever suits you.
With the device under test mounted on the base, press-fit test probes into the base. Use the handles on the test probes to rotate them, and tighten the wing nut when the needle is in position.
The needles are quite springy, so it’s easy to adjust their position with a pair of tweezers after they are approximately right. The heat-shrink on the needle helps with this, because it’s easy to grip with the tweezers.
Every single Sonoff model has used the Espressif ESP8266 / ESP8285 processor – until now.
But now ITEAD has gone in a different direction, and released the Sonoff BasicZBR3 which drops WiFi entirely in favour of Zigbee. It doesn’t even use an Espressif processor: instead it uses a Texas Instruments CC2530, which is based on the 40-year-old Intel 8051 processor architecture.
What is Zigbee, and how does it compare to WiFi? Is the Sonoff BasicZBR3 any good?
Zigbee is a wireless communications system that’s similar to WiFi in some ways, but they are optimised for very different purposes. They both use the 2.4GHz unlicensed ISM band, and they’re both based on standards managed by the IEEE: 802.11 for WiFi, 802.15.4 for Zigbee.
WiFi is optimised for devices with plenty of power available, and that also require very high throughput. It provides bandwidth in the region of hundreds of Mbps. Perfect for laptops, smartphones, tablets, and security cameras.
Zigbee is optimised for devices that need to run at extremely low power for a long time, and that don’t need to transfer much data. It provides bandwidth of 250kbps, so only about 1/1000th as much as WiFi. It’s suited to tiny devices that need to run on a coin cell for several years, and only pass small amounts of data. Great for temperature sensors and similar IoT devices that only need to send tiny amounts of data every few minutes.
Star topology vs mesh topology
WiFi uses a star topology, with each client device connecting directly to an access point. All communication is arbitrated through the access points, and end devices don’t talk to each other directly. The access points are linked together using some sort of backhaul, usually wired Ethernet. With this topology, you need enough access points to provide coverage of the entire area where you will be deploying devices:
Zigbee is much more flexible in its topology. It can be operated as a simple star just like WiFi, but it can also operate as a mesh because some Zigbee devices can act as relays to extend the coverage of the network:
There are three types of Zigbee device.
Zigbee End Devices (ZED) are nodes that only connect to one other device. They can enter a deep sleep mode to go offline when they aren’t sending data, so they can typically operate for 2 years or more from a tiny coin cell. Typical ZEDs include temperature sensors, light switches, and motion detectors. There can be many ZEDs in a typical Zigbee network.
Zigbee Routers (ZR) are nodes that don’t go into sleep mode. They stay awake continually, ready to pass on messages between other Zigbee devices. They are also functional devices in their own right: they include smart power plugs and light globes, because these typically have mains power available and can remain operating indefinitely. They don’t need to go into sleep mode to conserve a battery. With a few ZRs spread across your coverage area, your network can provide connections for many ZEDs.
Zigbee Coordinators (ZC) are the most important type of node. There can only ever be one ZC in each network. It always takes the first network address, and then it assigns addresses to all the other devices in the network as they join. You can think of it as being like the DHCP server in a typical LAN. Usually the ZC will also act as a gateway to other types of network, such as connecting your Zigbee network onto your WiFi network or wired LAN. Many home automation hubs can act as a ZC.
Pairing with Alexa
The Sonoff BasicZBR3 is wired up the same way as other Sonoff models, with active and neutral coming in on the input side on the left, and then going out to the load (such as a lamp) on the right. Follow the instructions provided by ITEAD and the guides in my previous videos to make the connections.
Once the BasicZBR3 is installed, turn on the power. It will begin in pairing mode, ready to join an existing Zigbee network. Startup is very fast, and it will be ready within a second or so.
You will need a home automation hub that can operate as a Zigbee Coordinator, such as an Amazon Echo Plus.
With the BasicZBR3 turned on and in pairing mode, and within range of your Echo, say “Alexa, discover devices.”
Your Echo will tell you that it is looking for new devices, and the BasicZBR3 will flash its output when it is discovered. The Echo will wait for some time in case there are devices that are slow to respond, so you will have to wait a minute before it will report back that it has found your new device.
That’s it, you’re done! You can now control the BasicZBR3 using commands such as “Alexa, turn on the first plug.”
Customisation of the node names can be done through the Alexa app.
CC2530 processor connections
Programming the CC2530 requires power to the device, plus DD (Debug Data), DC (Debug Clock), and Reset.
In the BasicZBR3, the output relay is controlled by I/O pin P0_7, and it reads the tactile switch using pin P1_3:
The BasicZBR3 provides the debug connections for the CC2530 in a handy 5-pin header, so if you want to mess around with the firmware and load your own code into it, these are the connections on the PCB:
If you write any custom firmware for the Sonoff BasicZBR3, please join the forum or Discord server and share your results.
If you don’t put USB on your project, you have to decide on a programming header to use. But everyone does it their own way: Sonoff has theirs, wESP32 has another, many projects have them and they’re all different!
That sucks, so let’s fix it by deciding what we think should be the conventional programming header format for our projects.
My goals are:
Define a convention for programming headers on ESP8285, ESP8266, and ESP32 boards.
Use that header in our own projects, so that it becomes common and interchangeable.
Lobby ITEAD to use the same header in future Sonoff models.
And the stretch goal: Convince Espressif to document it as a recommended header format for new ESPxx projects.
If we’re super-lucky, maybe we can convince ITEAD to fix the incomplete Sonoff programming header by adding RESET and GPIO0, and make all our lives easier in future.
We need to decide on a physical format, and also whether to supply 3.3V or 5V to the target board from the programmer. The pins we need are:
Physical format options include:
1×6 0.1″ header
2×3 0.1″ header
1×6 2mm header
2×3 2mm header
Something else? Ideas please!
The design considerations for the physical format include:
Similarity to existing designs including Sonoff, wESP32, ESProg, and ESP32 Programmer
Cheap and easy to use, with easy to source connectors
Small footprint on the target device
Perhaps leverage some existing standard such as P-MOD
Ability to mount permanently as a sub-board in the project if required
Considerations for the choice of 3.3V or 5V include:
Sonoff already requires 3.3V on the header
5V can be useful in some cases
Switchable voltage would be possible, but could be dangerous and would lead to fragmentation of the convention
Connection of programmer directly to VCC on target, compared to input of onboard 3.3V VREG
This has the advantage that it’s well documented, and many people have made adapters for it.
Already implemented on the wEPS32. 5V supply means the input can be diode-isolated from other supply sources on the board. 4 of the pins match the Sonoff header, except that Sonoff requires 3.3V so it’s not a perfect match.
wESP32-Prog header, but with 3.3V
This is the closest we could have to matching the Sonoff header while extending it to add the GPIO0 and RESET lines.
Documented by Espressif. Uses a 2×3 header, which is nice in terms of compact size. Unfortunately there’s no useful overlap with the ESP-01 header.
Doesn’t seem to match up with anything else in terms of pin order, but is perhaps the closest match electrically in a 1×6 format: all the necessary pins, with 3.3V supplied.
ESP32 Programmer by Mike Rankin
Nice 2×3 format header. If power was added this would be a nice format, but it doesn’t have anything to differentiate it from the ESP-Prog format from Espressif.
Other ESP32 Programmer by Mike Rankin
This one has a 1×5 header, which has all the pins we want except power.
Traditional house wiring has an active and a neutral that meander around the ceiling to each light location, with the neutral connected directly to the light. The active comes down through the wall to the light switch, and then the output from the switch goes back up the wall to the active side of the light fitting.
This works well with passive switches, but most smart light switches need a neutral connection to power their own electronics. With only the active wiring going to the light switch, it can be very difficult to replace existing switches with smart switches.
Building codes in many countries now require that all light switches must have a neutral connection, but this is a recent change so most existing houses don’t have a neutral wire at the switches.
Smart light switches that are designed to be installed in place of existing switches and don’t require a neutral connection are generally called “no-neutral” switches.
The Sonoff T4EU1C is a no-neutral smart light switch with WiFi, so it only needs the active-in and active-out connections that are already found at most light switch locations. It operates by drawing a small amount of power through the light even when the light is turned off, so that it can run its own electronics.
The T4EU1C consists of two PCBs joined together by an 8-way header. The top PCB is the low-voltage logic board, which includes the processor, WiFi antenna, 3.3V voltage regulator, touch sensor pad and driver IC, and the programming header:
The bottom PCB is the high-voltage mains board, which includes a 12V-output mains power supply, and a relay and Triac for controlling the active output to the load:
Re-flashing the firmware with Tasmota
WARNING: There are problems running Tasmota on this particular model. It worked for me, but many other people have problems with the touch switch even when Tasmota is installed correctly. The rest of the Sonoff operates properly and it can be controlled by WiFi, but the touch sensor doesn’t work. There are a few people collaborating right now to figure out why this happens. If you’re feeling lucky, you can give it a try. However, it’s possible that you won’t be able to use the touch sensor until this problem is solved. There is ongoing discussion about it on the SuperHouse Discord server so please join in.
Just like all other Sonoff models so far, the firmware on the T4EU1C can be replaced with alternative open-source firmware to add new features such as local-network operation, MQTT, etc.
However, out of all the Sonoff models that have been released this is perhaps the most difficult one to re-flash. It can be done if you have the equipment and ability to make soldered connections to very tiny parts on the PCB, and this particular board also seems to have some strange requirements to force it into bootloader mode.
The common process for putting a Sonoff into bootloader mode is to hold the GPIO0 pin low (ie: to GND) while powering-up the board. In my testing, I found that this would result in the Sonoff appearing to accept the upload of the new firmware, but a strange checksum error would occur in the flash memory and it wouldn’t boot properly afterwards.
The process that I’ve found to work requires making a connection to the RESET pin as well as GPIO0, so that it can be put into bootloader mode after it has already been powered-up and connected to the programming adapter.
Re-flashing the firmware on the T4EU1C requires the usual connections to the programming header found on the logic board as shown in the picture above, plus connections to GPIO0 and RESET to force it into bootloader mode. Connection to the programming header is easy, because it’s exposed on the logic board in the same format as almost all other Sonoff models.
The difficulty is gaining access to GPIO0 and RESET, because neither of these lines are brought out onto pads for easy connections.
The most convenient place to make a connection to GPIO0 is the very thin track that runs diagonally on the top side of the logic board. Use a scalpel to carefully scrape away some of the green solder mask along the track. Be very careful that you don’t cut the track, and don’t scrape away the solder mask from the surrounding copper areas. If you do, it will be much harder to connect a wire to the track without causing a short circuit to the surrounding copper.
RESET is even harder. The only place it is exposed is on the end of a tiny resistor labelled “R3”, with a very small gap to an adjacent resistor. The connection must be made very carefully and quickly. If the resistor is allowed to heat up for more than about one second, the solder on the other end will also melt, and the resistor will move.
To control the GPIO0 and RESET pins, I soldered a pair of momentary buttons together and connected 3 lengths of very thin wire-wrap wire to them:
The common (blue) wire is soldered to GND on the logic board.
One switched wire (yellow, in my example) is soldered to the GPIO0 track after scraping off the soldermask.
One switched wire (red, in my example) is soldered to the RESET line by attaching it to the bottom end of the resistor marked R3.
Be extremely careful when making these connections to the PCB. It’s very easy to damage the tracks or the parts, and if you don’t have the necessary equipment and skill to rework the board you may destroy your Sonoff.
Programming header connections
Use a USB-to-Serial adapter and jumper wires to connect the Sonoff to your computer. Make sure the USB-to-Serial adapter supports 3.3V mode, because the ESP8285 can be damaged if you connect 5V to it. The connections are the same as explained in previous videos:
In this case the power switch doesn’t matter, because we will use GPIO0 and the RESET line to force the Sonoff into bootloader mode.
The connections can be made with loose jumper wire, or you can use my Sonoff Programming Adapter which does the same thing.
The T4EU1C has the same pin assignments as a Sonoff Basic, so download the generic pre-compiled Tasmota binary.
Install the “Esptool” program, and open a terminal in the same directory as the Tasmota binary.
With the Sonoff connected to your computer as described above, and the buttons ready to assert GPIO0 and RESET, run Esptool as below:
You may need to adjust the serial port address to match your computer.
Immediately after you press “enter”, follow this sequence:
Press and hold both buttons that you have attached to the Sonoff.
Wait about 2 seconds.
Release the RESET button.
Wait about 2 seconds.
Release the GPIO0 button.
You should see Esptool immediately identify the processor on the Sonoff and begin uploading Tasmota. This entire process will take about 30 seconds. You should see output similar to this:
Serial port /dev/tty.SLAB_USBtoUART
Detecting chip type… ESP8266
Chip is ESP8285
Features: WiFi, Embedded Flash
Configuring flash size…
Auto-detected Flash size: 1MB
Compressed 515872 bytes to 355877…
Wrote 515872 bytes (355877 compressed) at 0x00000000 in 31.3 seconds (effective 131.7 kbit/s)…
Hash of data verified.
Hard resetting via RTS pin…
At the end of the upload, Esptool will report 100% completion and say that it is resetting the board. However, it can’t actually reset the board because it doesn’t have any connection to the RESET line. You can press the reset button yourself, or disconnect the Sonoff from the programmer and re-connect it to cycle the power.
The Sonoff will then begin the normal Tasmota setup process, creating a WiFi network and opening a serial connection through the programming header. Follow the usual steps as shown in the Tasmota documentation to set it up, selecting “Sonoff Basic” as the module type.
The T4EU1C should then behave as expected, with control using the touch sensor on the front panel and also via WiFi.
ESP8266 / ESP8285 boot messages
If the ESP8285 didn’t enter bootloader mode properly, the Tasmota upload may have appeared to work in the previous step but the Sonoff still won’t boot. Esptool can show its normal upload progress, ending with the message saying it is 100% complete and resetting the board. But then when you power cycle or reset the board, it never comes online and you can’t tell why.
While booting, the ESP8285 outputs debug information to the programming header at the unusual baud rate of 74880bps. Most serial terminal programs can’t operate at that speed, because it’s not a standard baud rate.
The “CoolTerm” serial console is available for Mac, Linux, and Windows, and can be configured to support 74880bps.
Download and install CoolTerm following the instructions on its site.
After it has been installed, find where the binary is located on your computer. On a Mac, it’s typically inside the “/Applications” directory.
In that same directory, make a text file called “baudrates.ini” and put in the number “74880” without quotes or any other characters. Save the file, then start up CoolTerm.
You should now find 74880bps listed as a supported baud rate in the “Options” menu.
Select 74880 as the baud rate, select the serial port for your programming adapter, and click “OK”:
Click the “Connect” button to open the connection to your Sonoff, and then press the reset button on the Sonoff to force it to reboot.
If the ESP8285 has failed to boot, it will display an error similar to this:
The original Sonoff Basic didn’t have any provision for an external button or switch. One of the most common hacks is to add a switch, so ITEAD decided to make it easy and put screw terminals right there on the Mini.
The Mini is also the smallest Sonoff model so far, which makes it ideal for retrofitting behind an existing switch. Combined with the screw terminals to connect the switch, the Mini is probably the best general-purpose Sonoff for anyone wanting to retrofit home automation to an existing home.
The S55 is an exterior-rated GPO (General Purpose Outlet) or power point. It allows you to have both local control of the power point using a button, and also control from your home automation system.
Both are nice devices, but they become even better when the amazing Open Source Tasmota firmware is installed on them.
Over the years there have been many methods developed to do OTA (Over The Air) replacement of the existing Sonoff firmware with an alternative such as Tasmota. However, I’ve found that these methods are either frustratingly complex or just stop working because ITEAD change things with new releases. I don’t even bother trying these methods anymore: I just go straight to connecting a USB-to-Serial adapter to the programming pins on the Sonoff’s processor. It can be tricky to get the connections sometimes, but it’s guaranteed to work every time single time.
Warning: Do not attempt to connect a programming adapter to any Sonoff model while mains power is connected. ALWAYS disconnect the Sonoff and power it ONLY through the 3.3V connection.
Install Tasmota on Sonoff Mini
The programming connections for the Sonoff Mini are provided on tiny flat pads on the bottom of the PCB:
The button on the top of the PCB is connected to GPIO0, so if you connect to GND, 3.3V, TX, and RX, you can put the Sonoff Mini into programming mode by holding down the button while connecting power from the programmer.
Unfortunately the pads on the PCB are very small, so soldering jumper wires onto them is tricky. If you have a small soldering iron and good eyesight (or magnification) you can solder wires directly onto the pads.
Just be careful you don’t apply too much heat, because the pads can come away from the PCB!
To get around that problem I used my 3D printer to make a programming jig using a design published on Thingiverse. This programming jig uses “pogo pins”, which are spring-loaded pins that can make temporary connections to a PCB. Pogo pins come in a variety of sizes and shapes. I used P75-B1 pins, which means they have a 0.75mm diameter pin with a simple conical point:
This design has 3 parts: a base that holds 4 pogo pins, a small spacer that slips over the pins to help keep them aligned, and a top that goes over the pins and then provides alignment guides for the Sonoff Mini.
I used super-glue to attach the top to the base, once I’d checked everything was aligned:
The Sonoff Mini can be attached using an elastic band:
The pogo pins push against the pads on the PCB:
Hold down the button on the PCB while plugging in the programming adapter to force the Sonoff to go into programming mode, then you can use Esptool or whatever other method you prefer to load the Tasmota binary. In my case I used Esptool, and the command looked like this:
However, this command is specific to the USB port that I used on my computer. You may need to adjust the command to suit your needs. This is all documented well on the Tasmota site.
Because the Sonoff Mini has different pin arrangements to a normal Sonoff Basic, and it’s designed to use a normal switch instead of a button, you need to load a special configuration for it.
After you’ve been through the normal Tasmota setup process and connected it to your WiFi as described in the Tasmota docs, go to the Tasmota templates site at blakadder.github.io/templates/ and search for “Mini”. You’ll find a template that looks like this:
In the Tasmota interface, go to Configuration -> Configure Other and paste the template into the “Template” field.
Make sure the “Activate” check-box is ON, then click “Save”.
Your Sonoff Mini will now operate as expected, with the external switch operating in the normal way.
Install Tasmota on Sonoff S55
The Sonoff S55 doesn’t have a “DIY mode” jumper, so that’s not an option. Luckily, the usual programming header is provided on the PCB ready for you to solder on wires, solder on a header, or just press connections against it. The button for external control is linked to GPIO0, so it’s very easy to put it into programming mode.
The header is in the normal 0.1″ pitch so it’s large enough to solder on a header directly. There’s no need to use a complex pogo pin programming jig.
Solder some hookup wires directly onto the pads, or solder on a header:
I soldered a 4-way 0.1″ header socket onto the pads, with the pins bent a little sideways to make the head sit almost horizontal with the PCB. This makes it easy to plug in a Sonoff Programming Adapter, or use jumper wires to your own USB-to-serial converter.
Hold down the GPIO0 button while you connect the programming header to put it into programming mode, then follow the normal instructions for installing Tasmota. This is very well documented on the Tasmota site.
There’s no specific device profile for the S55 in Tasmota, but it uses the same pinouts as the Sonoff S26 and other mains-plug adapters. Simply select “Sonoff S2x” as the module type in the configuration interface, and it will work as expected.
I’ve resisted for ages, so viewer Lorenzo took matters into his own hands and set up a Discord server for SuperHouse 🙂
Within 24 hours of being announced, there are now more than 200 people on the server! To join the discussion about SuperHouse projects, home automation, MQTT, Home Assistant, OpenHAB, Tasmota, and many other things, go to this link for an invitation:
Livestreams are back! My new Internet connection is working, so it’s time to warm up the camera and get back into live-streaming.
EAGLE’s “managed libraries” feature and its Fusion 360 integration are two of the biggest and most important changes to EAGLE in years, but they’re still very frustrating to use and a bit rough around the edges. The first time I tried using managed libraries I almost rage-quit in frustration, but now that I’ve figured out the magic workflow I’ve come to love them.
To demonstrate both managed libraries and Fusion 360 integration, I’m going to take one of my older designs (the Freetronics EtherTen) which hasn’t been touched in years, and give it a major makeover:
Replace all the parts in the design with parts in managed libraries
Make sure all the parts have associated 3D models
Sync the design with Fusion 360 so it can be used as the basis of a 3D design
Come and join me at 9am Saturday morning (Melbourne time, GMT+10) to see how badly I can stuff this up! Subscribe and click the bell icon on my channel to be notified when the livestream starts:
My original design for the Sonoff Programming Adapter had a power switch on it, but the switches turned out to be rubbish quality so I put on pin headers instead.
Now I’ve updated the design based on feedback in the forum, so they’ll have a normally-closed button in the power line and will ship with both a socket and a pin header so that you can decide which one you want to install.
Colin Hickey has an interesting YouTube channel that features some of his cool home automation projects. What I like about his videos is that he doesn’t just show the end result: he goes through his setup step by step so that you can do the same thing yourself.
If you go back through his videos you’ll find plenty of fascinating information about his home-made PowerWall and battery management system.
His latest video should be interesting to anyone who has an iLife robot vacuum cleaner, so check it out and make sure you subscribe to his channel:
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