Category: How To

Flashing Tasmota over serial

In my previous post on Tasmota I was able to make use of tuya-convert which supports over the air (OTA) updating a ‘smart wifi’ device to the Tasmota firmware. Tuya-convert relies on exploiting a defect in the firmware, Tuya has patched this bug and some (many) device manufacturers have started to ship updated versions of the software – and in some cases new, non-ESP based hardware. Thankfully many devices are still based on ESP hardware and many of the circuit boards even have test points exposed that make hooking up a serial adapter possible for someone comfortable with a soldering iron.

The Tasmota doc is a great place to start. The device I’m working on is a Gosund Smart Light Switch SW5. I did try tuya-convert on this and got the id2 response which indicates that there is a newer firmware. Opening up the lightswitch was easy, but you will need T6 torx screwdriver. Once the circuit board was out I could take a close look.

We can see that the chip is an ESP-8285, that will let me find the data sheet and figure out the pin outs. We can also use the Tasmota doc on pin outs as a reference. Right at the top of the image you can see test / solder pads on the edge, these are going to be useful.

I’ve annotated the chip diagram to show the pins I’ll need to flash the device. It’s hard to tell from the photos I’ve shown so far the scale of the chip, but I can tell you that I don’t have the skills to solder directly to the pins of the chip – I’ll need to use the break out pads on the side of the circuit board. Even those solder pads are very small.

I confirmed based on the data sheet that the break out pads mapped to the pins I had identified on the chip using a multi-meter. The pins on the chip are very small and I was working by feel mostly, but it gave me enough confidence that I could use the break out pads to do the connection.

It is very important to only power the ESP-8285 with 3.3V. If you use 5V you are very likely to break things permanently. Off to eBay I went to pick up what I thought was one of the recommended CH340G serial adapter boards. I later learned that the one I bought did not have a voltage regulator making it unable to supply enough power for the ESP-8285.

You can see that while this board supports 3.3V or 5V – you must modify the board to break the solder bridge to the 5V and add one to the 3.3V. I was able to verify the voltage was 3.3V after my modification with a multi-meter.

At first I had decided because the break out pads were evenly spaced and about the same spacing as a pin header. I did try this – but got stumped by the fact that if I did hook it up correctly the LED on the CH340G adapter would go out and things didn’t work. This turned out to be due to the fact that this adapter would not supply enough power to the ESP-8285. This approach might work, but soldering to the pads was easy enough and that’s the path I ended up taking.

I decided to use Linux and the esptool to do the flashing. It turns out that I could just use pip to install the esptool.

On Linux, if you haven’t modified your user to be in the right group you may not be able to use the /dev/ttyUSB0 device. There may also be additional things you need to do in order for the adapter to be recognized by the OS. I’ll leave these challenges up to the reader to overcome with some creative use of a search engine.

Here are the results of my soldering job – along with a micro-SD card for a sense of scale. This is very small but it’s not too difficult if you use a few tricks. Solder paste on the pads applied with a toothpick are a big help to get the solder to flow. Pre-tinning the wires helps. Working under magnification helped my aging eyes. Make sure the soldering iron is completely warmed up. Also add a little solder to the tip of the iron (pre-tin the tip). With these preparation steps, it should be easy to just touch the iron and the wire to the pad and the solder will flow and you’re good.

Initially I had wanted to avoid soldering, but it turned out to be very quick and easy to do. The reliability of the connection is also superior to trying to press fit the wires – and creating a jig would take a lot more time. In future when I need to flash over serial I’ll just go warm up the soldering iron.

I then decided the correct wiring to perform. Note that TX/RX are swapped. IO0 is pulled to ground to force the ESP into programming mode.

It was here where I ran completely into the wall trying to use my cheap eBay CH340G adapter. I did find someone else who’d succeeded flashing the SW5, which gave me hope that I could succeed. It turns out there is a friendly community you can connect with on Discord to talk about Tasmota things. I started a conversation in the #flashing-issues channel and after a short while got some helpful advice.

Now it turns out, I’d been hasty. If I’d done more research I would have found that having a stable 3.3V power supply wasn’t a given for all of the adapters. While the golden CH340G can be had for a few dollars – many of the CH340G adapters do not have a voltage regulator on them and will not work with the ESP devices. Once the Discord folks had kindly educated me on this – I created a pull request to add some additional warnings to the doc (which has been merged).

Fellow Canadians might be able to grab one of these CH340G adapters from Amazon, it has the required voltage regulator. In my case I dug through my pile of electronic projects and  came up with a Circuit Playground Express, it has an onboard voltage regulator and will easily deliver the ~150mA that the ESP needs (as long as I’m not trying to drive the onboard LEDs).

This changes my wiring diagram. I’ve abbreviated Circuit Playground Express (CPE).

By connecting all the GND lines together I ensure both devices are using the same reference. I’m pulling the 3.3V from the CPE, but the CH340G adapter is being used for the programming. This worked like a charm, but was a mess of wires.

Now that I have stable power, I can follow the steps.

1. Backup firmware

Unplug the connections and do them again – (power cycles the setup)

2. Erase flash

Again, reset the world

3. Upload tasmota.bin – make sure you get the right firmware.

Now you can test your work by providing only power (GND and 3.3v) to the SW5 device to see if the Tasmota firmware starts up ok and offers a WiFi access point (tasmota_XXXXXX-####). You can even go through the initial setup and get it connected to your network.

After I’d gotten my SW5 running Tasmota, I then re-assembled the actual light switch. I found that you had to carefully tighten the screws to avoid binding the switching action. I then temporarily wired this to house wiring to confirm that all of the functions worked as expected. Once things were good, I could permanently install this in my desired location.

I’d referenced flashing Tasmota over serial as the ‘hard way’ – but as long as you can disassemble the device to get to the circuit board, and there are test points you can solder to – it isn’t all that hard. You do need to be comfortable with a soldering iron, and have the right gear to program 3.3V serial.

Ubuntu adding a 2nd data drive as a mirror (RAID1)

Over the years I’ve had the expected number of hard drive failures. Some have been more catastrophic to me as I didn’t have a good backup strategy in place, others felt avoidable if I’d paid attention the warning signs.

My current setup for data duplication is based on Snapraid, a non-traditional RAID solution. It allows mixed sizes of drives, and the replication is done via regularly running the sync operation. Mine is done daily, files are sync’d across the drives and a data validation is done from time to time as well. This means while I might lose up to 24hrs of data if the primary drive fails, I have lower usage of the main parity drive and I get the assurance that file corruption hasn’t happened.

Snapraid is very bad when you have either: many small files, frequently changing files. It is ideal for backing up media like photos or movies. To deal with the more rapidly changing data I’ve got a SSD drive for storage. I haven’t yet had a SSD fail on me, but that is assured to happen at one point. Backblaze is already seeing some failure rate information that is concerning. Couple this with the fact that my storage SSD started throwing errors the other day and only a full power cycle of the machine brought it back  – it’s fine now, but for how long? Time to setup a mirror.

For this storage I’m going back to traditional RAID. The SSD is a 480GB drive, and thankfully the price of them has dropped to easily under $70. This additional drive now fills all 6 of the SATA ports on my motherboard, the next upgrade will need to be an SATA port expansion card. I’ve written about RAID a few times here.

I’ve moved away from specifying drives as /dev/sdbX because these values can change. Even this new SSD caused the drive that was at /dev/sdf to move to /dev/sdg allowing the new drive to use /dev/sdf. My /etc/fstab is now setup using /dev/disk/by-id/xxx because these are persistent. Most of the disk utilities understand this format just fine as you an see with this example with fdisk.

Granted, working with /dev/disk/by-id is a lot more verbose – but that id will not change if you re-organize the SATA cables.

Let’s get going on setting up the new drive as a mirror for the existing one. Here’s the basic set of steps

  1. Partition the new drive so it is identical to the existing one
  2. Create a RAID1 array in degraded state
  3. Format and mount the array
  4. Copy the data from the existing drive to the new array
  5. Un-mount both the array and the original drive
  6. Mount the array where the original drive was mounted
  7. Make sure things are good – the next step is destructive
  8. Add the original drive to the degraded RAID1 array making it whole

It may seems like a lot of steps, and some of them are scary – but on the other side we’ll have a software RAID protecting the data. The remainder of this post will be the details of those steps above.

Continue reading “Ubuntu adding a 2nd data drive as a mirror (RAID1)”

OpenWRT Guest Network (and beyond)

As my kids get to the age where both they and their friends have devices, this means granting access to our internet to a growing circle of people. OpenWRT has the ability to support guest networks and I’ve been meaning to set this up for some time.

Beyond simply having a guest network, I also want to setup an IoT network where I can isolate some of the network enabled things but not give them wide access to the rest of my internal infrastructure.

Let’s start with a simple guest network setup. This is well documented on the OpenWRT site. I’ll be using the CLI instructions to make these changes. FWIW this is based on the 21.02.0 version of OpenWRT.

The first part of this will be pretty much copy and paste from the OpenWRT instructions:

I of course modified the ipaddr for my setup, but pretty much used the command as is.

On the Web UI (LuCI) you should now see under Network->Interfaces a new Guest network. All of the changes landed in the /etc/config/network file.

Now we setup a wireless network configuration with the first radio

Again, I’ve pretty much followed the directions but have customized the SSID and not shared the password. I’ve rolled in the extras to isolate guest users and use encryption.

The LuCI web UI now looks a little more concerning (Network->Wireless)

But.. the previous Network->Interfaces now seems to have come to life.

Still the expected changes are reflected in /etc/config/wireless.

It took a bit of head-scratching, but I figured out what was wrong. I had not specified a wireless.guest.key that met the minimum length (8 to 63 characters) – this apparently caused everything to go sideways. Once I fixed this my new wireless interface came to life.

Let’s continue on with the DHCP configuration

And the Firewall

Now not only should you be able to see the new WiFi SSID available to connect to, but when you do you will be isolated from all other devices on the network and only able to see the internet. A network scan will turn up the existence of the router, but attempts to connect the web UI fail – that’s pretty cool isolation.

Devices connected to the guest network still show up in the OpenWRT status page. They are assigned a DHCP address from the network.guest.ipaddr subnet, which is distinct from my normal network.

Apparently I do give up a little performance having two (or more) networks hung off of the same radio, but the utility of having a restrictive guest network is pretty cool.

The Archer C7 has two radios, and we’ve not configured the guest network on the second radio. Let’s do that now.

Cool – now I have a guest network that is on both radio bands. You’ll note that I run both access points with the same SSID, this mostly just works and devices figure it out. I even run my dumb AP with the same SSID. This is one approach that works and let’s people move around the house with seamless connections.

I do know that some people try to force a device to a particular radio type, and will run their legacy network on a different SSID. This is of course also valid, it really depends what you’re looking to achieve. I’m taking the simple to configure devices approach, and giving the devices the responsibility to work out which radio band and which access point to connect to.

Now let’s create a second ‘guest’ like network for IoT devices. This time I’ll just combine all of the steps together

Nice – now I have a third subnet which will hand out DHCP addresses valid for 24hrs. The devices are all isolated from each other.

For devices on the IoT network, while I don’t want the device to be able to see anything other than the internet – for my own monitoring and use, I’d like to be able to see the devices on the IoT network from my normal lan network. This turns out to be very easy.

Connecting to the IoT network and doing as scan, shows me that I can only see myself and the router (because the device has to send traffic somewhere). Again, with the isolation I can’t connect to the web interface of the router. However, with this new “zone->forwardings” I can from my lan network see devices on the IoT network. Super cool, and actually very easy.

There plenty more tweaking we can do here, but to avoid going too far down the rabbit hole we’ll stop here.