Actually, these features have been there for a while now. I didn’t mention them just to make sure that the older PCB revisions are sold out and if you’re making new purchases, you’ll get the new PCBs with these features.
One of the features is a 5-pin USB header. You already have a microUSB connector so why another USB? This is because you can more easily route cables. A microUSB connector requires a microUSB plug, which requires about 2 inches or 5cm of space beyond the board’s edge. A 5-pin female header to USB-A cable with the 5-pin male header requires zero inches or cm. This makes the board fit inside smaller enclosures or leaves more space for other devices inside the enclosure.
Have a look at the following photo for a comparison:
Another feature is a header near the analog/digital input terminal block header. This header is a reorganized header from the analog/digital input terminal block. It brings out 5V, channels 3,2,1,0, and GND. This header makes it easier to connect these channels to a 4-relay module to control relays like this one (header on bottom right):
Even though these 4 channels are advertised as input channels, there are actually commands to use them as output channels! This way you can read your SDI-12 sensors and then actual relays to do irrigation or fan control all on this one board!
Recently a customer asked me whether there can be a UART interface to integrate the SK-16 adapter with an ESP32 adapter. I thought, why not? So, after some soldering, I modified a regular SK-16 USB adapter into a UART adapter. It has 5V, GND, TX at 5V, TX at 3.3V, and RX, all brought out on the expansion port.
Here is a photo of the modified adapter with an ESP32-WROVER dev board and an old Decagon soil sensor. I tested the whole thing first with a USB-UART adapter and then with the ESP32 running MicroPython.
This modification took a while so it’s ok if it’s just once in a while. But if you want a few of these, I may consider making a version of the board. Leave me some comments.
Here is a tricky thing I had to do to make this modification:
What we are looking at is a slotted screwdriver. The blade rested on a very tiny piece of wire I had to solder between the square IC and the rectangular IC. The pitch of these ICs are less than 0.05″ or about 1mm. If I went ahead to solder one side, then soldering the other side will cause the soldered side to melt and I ended up desoldering the wire because it’s so small. So I used the screw driver to both pin the wire down and provide thermal relief to the soldered side.
Here is another idea. What if I added female headers so I can just drop an ESP32 dev board on to the SK-16 board? No soldering and no wiring, great!
The above is just a mock-up. But the only problem is that there are so many ESP32 dev boards and they all have slightly different pinouts and spacing between the rows of pins. This will have to be custom-made to fit the ESP32 dev boards you use. If you are interested, leave me some comments what ESP32 boards you use. The one photographed is an official Espresiff dev board, ESP32_Devkit_V4. It has wider spacing between the two rows of pins but the pins are clearly printed next to the pins.
Every time I type a question into Google AI, I wonder if that caused a tree in the Amazon or something. AI is very hardware and resource intense to run. I read about how the skyrocketing RAM price from the AI boom is causing Apple to quietly discontinue their top-tier local-AI-running desktop with 512GB of RAM and bumped up prices for lower tier ones with 256GB and 64GB RAM. People trying to run their own AI models are scrambling to find those top-tier Macs whole some are price gouging, sometimes $10K more than the price just last year!
Here is how that apocalypse might be affecting us. Enter, 2025 vs 2026 May chart. I know that many of us use Raspberry Pi 5 computers to run data logger routines, which is fine, but the price hike has changed the overall behaviors of my customers for sure. I plotted out the price of RPI5-8GB May 25 vs May 26, a whopping $120 increase from the $80 price that I personally paid last May for a couple of them! See the blue line.
Now, also see the orange line of SDI-12 microUSB units sold, about a 50% decline! I bet that was related to the rarity and high price of RPIs! But at the same time, the miniUART module sales really took off! See the green line. From not selling much at all to overtaking microUSB units! I bet more and more customers are using microcontrollers like Arduino, or ESP32, or Raspberry Pi Pico (not Pi, Pi Pico), to make their data loggers to save cost!
So, I am inclined to use this summer to release more videos and sample code to aid the transition from microUSB adapters to miniUART modules, targeting the three most common microncontrollers, Arduino nano ESP32 with C/C++, ESP32 dev board with MicroPython, and RPI PicoW/Pico2W with MicroPython. If you think this is a good idea and it helps your, please put in some comments so I know I’m headed in the right direction.
After some requests from customers, I have decided to design a small module that can help everyone prototyping and embedding SDI-12 in their own designs. Enter, mini (rewind! I should have posted this piece last year but forgot it was still in draft mode!)!
This mini module measures only 1″ by 1″ (2.54mm*2.54mm) and is a quarter the size of the regular adapter:
mini vs regular
The immediate advantage is you can easily place it on a breadboard for prototyping like this, with an ESP32 dev board:
mini with ESP32 dev board on breadboard
The size of the mini is designed so that there is one hole on the breadboard for each connection. Some dimensions in mm. Notice there are two mounting holes in case you wish to mount this on your circuit board securely:
mini dimensions
The relative locations of the 6-pin ICSP header, the bottom-right mounting hole, and the top right SDI-12 bus hole are unchanged from the regular board so I can still flash firmware on this board using my existing programmer!
Here is how I connected the module to my ESP32:
breadboard for mini
So I first put my ESP32 on the breadboard, with 5V connected to to top red and gnd to top blue. I also connected 3.3V to bottom red (not used) and gnd to bottom blue.
Then I connected 21 to 5V and 25 to gnd, both to top power strips. I also placed a 0.1″ jumper between 21e and 22e, another one between 24e and 25e. This is to make 22 5V and 24 GND, to match the module, and also keep the 22a-24a available to connect a TRS adapter to connect to an SDI-12 sensor.
Also, I connected 22j to gnd on bottom, and 23j (orange wire) to module TX3 which connects to my ESP32 serial port 1 RX, and 24j (yellow wire) to module RX which connects to my ESP32 serial port 1 TX.
mini with ESP32 dev board hooked up
Notice that because of the 0.1″ jumpers, my 22a is 5V and 24a is GND. The original pin on the module for this pin is NC or not connected, so you can jump GND to it with no issues. That also leaves 23a as SDI-12 signal. I then placed a TRS adapter in pins 22a-24a, with tip connecting to 22a (5V), ring connecting to 23a (SDI-12 signal), and 24a to GND:
mini with ESP32 dev board trs adapter and sensor
You can’t really see which pins I connected to ESP32 because my ESP32 dev board doesn’t have silk screen on top. I was using pin 13 for serial port 1 TX and pin 34 for serial port 1 RX. You can use what fits you.
If you want to use a raspberry pi pico instead of an ESP32, here is how I wired them together.
Here is a screen recording on my computer. You can see how I was reading from the mini module and SDI-12 sensors. It’s very similar with both pico and ESP32 dev boards because I am using micropython on them both.
