Sensorgnome power
Providing good power to Sensorgnomes and to the radios can be more challenging that it may seem and can result in difficult to troubleshoot issues.
When providing power to a Sensorgnome there are multiple aspects to consider:
Powering the Raspberry Pi, which typically also powers the radios attached via USB.
Ensuring that the Raspberry Pi can indeed power everything attached to the USB ports.
Dealing with power when using Solar and battery systems.
Powering USB devices
While the USB specs have a lot of rules about how much power each device may use there is a simple rule for Raspberry Pis (at least for the 3B and 4B models):
Once the power limit is exceeded the USB power is cut and devices misbehave. FUNcube dongles consume 100mA-200mA, CTT radios less than 30mA. This means that 4 FCDs and 4 CTT radios can be powered by the rPi directly. A USB GPS can also be added. The majority of cellular modems have power consumption spikes that exceed 1.2A or at least come close to it, so they cannot be powered reliably from the rPi ports. To connect a cellular modem use a HAT (printed circuit board that mounts on the rPi's 40-pin connector) or attach the dell modem to a powered USB hub.
Powering the Raspberry Pi
The power consumption of rPis is very spiky, consuming 1A-2A at peak. All the devices attached to the USB ports and potentially a cellular HAT must be powered as well. The result is that you need to use a power adaptor that can deliver more than the typical 2.1A claimed by many power adapters. Most el-cheapo "2A" or "2.1A" adapters lead to problems sooner rather than later.
When a Sensorgnome isn't receiving enough power -- that is, the voltage and/or current is lower than the device is rated for -- it can result in a malfunctioning station that doesn't collect data.
Using Power over Ethernet (PoE)
While Raspberry Pis don't have power-over-ethernet (PoE) built-in it is possible to use PoE with "splitters" that separate the power and ethernet at the device end. For reference, a good page about PoE is https://en.wikipedia.org/wiki/Power_over_Ethernet and it's ... confusing... The table at the end of the page in the Pinouts section is a good summary.
The recommended set-up with PoE is to use a PoE switch (which will most likely use "gigabit mode A" in the table) and a splitter with a built-in voltage converter. The splitter to use depends on the rPi model: for an rPi3 get a splitter that provides 5V on a micro-USB connector (example https://www.amazon.com/gp/product/B07CNKX14C), for an rPi4 get a USB-C splitter (example https://www.amazon.com/UCTRONICS-PoE-Splitter-USB-C-Compliant/dp/B087F4QCTR), for a SensorStation get a splitter that provides 12V (example https://www.amazon.com/gp/product/B0CL2CBS75/). For a rPi4 it may be advantageous to use a splitter that supports PD (power delivery) so it outputs 5.1V, but those are more pricey and possibly overkill. The above links are intended as suggestions not recommendations as the longevity of these devices has not been tested, there are definitely more "industrial" versions available.
Overall, the important part is to ensure that the switch/injector and splitter match. Virtually all PoE switches in 2024 are Gigabit 802.3af (48V) compliant (or more advanced 803.2at/bt) and use "mode A" (see Wikipedia table). Using a "gigabit" and/or "802.3af" splitter ensures compatibility assuming it's properly made.
A common alternative that historically predates 802.3af is to use 2 wire pairs for 100Mbit ethernet and 2 pairs for 24V. This is still common in Ubiquiti equipment as well as that of other vendors, which perpetuates the confusion. In addition, this mode of operation is "covered" by 802.3af mode B, except that 802.3af requires 48V, not 24V. But 802.3af splitters as mentioned above should work fine with 24V too.
One catch with non-gigabit splitters (e.g. the 24V set-up) is that if they are used to connect two gigabit devices (switch and rPi) then it is often necessary to force the use of 100Mbps at one of the two ends, i.e. either using the switch web interface (in the case of a managed switch) or ethtool on the rPi.
Underpowered Sensorgnome - how does it occur?
Underpowered Sensorgnomes typically work fine when set-up and it's later that problem crop up. Sometimes they reboot but more often some peripheral malfunctions. Often USB-attached devices restart on their own. In some situations the Sensorgnome just seems "flaky" and a different problem crops up every time.
The easy cases to troubleshoot are due to inadequate components and installation problems because they tend to show up quickly. Check components, have spares to swap-in to verify against, check all connections and connectors.
The troublesome cases are when general wear and tear triggers the problem. This is because USB cables and power cables experience a fair bit of strain over their lifetime from repeated bending. The following problems have been identified at Motus stations in the past:
The connection to the screw terminals on the DC-DC voltage converter is loose
Individual copper strands within the USB cable are broken. This can occur from repeated bending of the cable.
The microUSB port of the Raspberry Pi is damaged (lifts from the circuit board slightly when force is applied).
Due to nightly deep discharges the off-grid battery can no longer reliably power the Sensorgnome through the night.
Due to humidity and heat-cycling connectors become unreliable.
Identifying an underpowered Sensorgnome
The behaviour of underpowered devices can be inconsistent and hard to diagnose. In some cases, it is not possible to connect to the device because both Ethernet and Wi-Fi are malfunctioning, however it may still appear as though the device is on as the indicator LEDs will be blinking. This can also be due to corrupted data on the SD card or a physical connection problem with the SD card, so it's not always obvious.
Fixing power supply issues
Always keep a spare micro USB cable handy, one that has at least 22 gauge power delivery. See USB Micro B Male cables for power delivery.
In most cases, fixing the issue is as simple as replacing the Micro USB cable which plugs into the Raspberry Pi. It is also possible to swap out the DC-DC voltage converter to a device that is rated for more current and/or voltage (no more than 5.1 V, however!), but these have not been tested. See: DC-DC Voltage Converters for Raspberry Pi (not tested).
USB Micro B Male cables for power delivery
Currently available (as of Nov 3, 2021) cables are listed below:
DC-DC Voltage Converters for Raspberry Pi (not tested)
Currently available (as of Nov 3, 2021) DC-DC converters are listed below. Please note that these models have not been tested, but are expected to perform better the default model.
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