Upgrades to the SDI-12 USB adapter

I have been working on some updates to the SDI-12 USB adapter so that it would add more features to a data logging system. So far, I’ve updated the PCB (left board) to include additional connectors. The top of the board will have 4 analog channels. This is not as accurate as the red SDI-12 + Analog USB adapter boards. The SDI-12 + Analog USB adapter has practical accuracy of 20 microvolts and has differential input channels. The 4 channels on the basic SDI-12 USB adapter have accuracy of about 5 millivolts. Also there is not a voltage reference so the measurement will be affected by the USB voltage, which is only nominally 5V. Nevertheless, if there are some sensors that output voltages in 0-5V range you want to log with moderate accuracy, such as a potentiometer, or a thermistor for approximate temperature calculation, you can use these channels. The breakout looks the same as the SDI-12 + Analog USB adapter. There are no serial resistors so you have to add yours if you want to convert resistance to voltage.

I will release a new firmware version on these newer boards. At the same time, I am considering adding digital counting features to these analog channels so if someone wants to count pulses such as flow meters or rain gauges, they can use these channels for such purpose. I plan to develop this part in the summer.

Another connector (bottom one on left board) I have added will connect the adapter to an analog extension board (right board), which sports the same 20 microvolt accuracy as the SDI-12 + Analog USB adapter, in case you want to add these channels say for pyronometers or other low voltage and high precision measurements after initially getting the basic adapter. You can stack up to 4 such analog extension boards. Each board has an address jumper (right board, white rectangle) for one of the four addresses the analog-to-digital converter supports. That gives you a total of 16 high-precision analog input channels. Each extension board also comes with a few additional connectors for SDI-12 sensors as an option. You can more easily wire up more SDI-12 sensors to the adapter. I don’t recommend wiring up more than 6-8 SDI-12 sensors to the same adapter. Some sensors come with strong pull-down resistors. When too many of them are wired to the same adapter, they may prevent some other sensors from correctly communicating on the bus.

The last connector (left board middle) I have added will help developers using MicroPython platforms easily connect to it via serial ports, since most MicroPython boards don’t have USB hosts. I will start shipping these newer SDI-12 USB adapter boards soon although new firmware that makes use of these features will have to wait until later.

Will this affect your existing projects? Very unlikely. The new adapter has all the features of the old adapter. The SDI-12 + Analog adapter will still be around since it is a nice compact form factor. The new SDI-12 adapter plus the analog extension board will be approximately the same price as as the SDI-12 + Analog adapter.

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