This project provides build instructions and 3D print files for a basic but powerful DIY Meshtastic node with the following features:
- Pocket sized
- Battery powered, ~40 hour run time (Up to 2 weeks with double 18650 version)
- ~1 watt maximum output on internal battery power
- ~2 watt maximum output on USB power
- Based on two easy-to-obtain COTS modules
- Relatively easy assembly and soldering with no custom PCB required
- Optional GPS, OLED display, and Rotary encoder can be added for standalone operation
The castellated edge connections on the E22 module, along with the pin assignment flexibility of the NRF52 MCU, allow most signals to pass between boards with no wiring. Just careful positioning, a little solder, and three header pins connect all signals. Point-to-point wiring is used only for power and peripherals.
The E22 gives this node outstanding performance in a compact package with longer range than most commercially available pocket nodes. The hinged and swiveling antenna matches the physical design of the node, shielding the battery power switch from accidental bumps. This node works well when folded, yet makes no compromises when straightened up at your destination.
The core of this build can also be used in solar nodes; see the note in step 11 and the techincal notes at the end.
These instructions assume you have basic electronics soldering equipment, supplies and tools, and are reasonably competent at soldering surface mount and thru-hole PCBs. If you have no experience soldering, don't give up; you can probably learn to solder in a few hours. There are plenty of tutorial videos out there. But don't do your early practice on this project.
Similarly, it's best if you are familiar with other Meshtastic nodes as this is not an introduction to Meshtastic.
Note: Product links are examples of components with the required specifications and do not imply a recommendation of a specific part or supplier. These are not affiliate links.
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"Pro Micro compatible" NRF52840 dev module
Such as the Teyleten, Tenstar Robot. Some of these can be found for less than $3 each.
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Ebyte E22 900M33S LoRa module
Usually $15-20, available from Amazon or AliExpress.
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1000mAh LiPo cell with protection board or Li-ion 18650 cells
The 50mm x 20mm x 10mm cells from Amazon or AliExpress fits the smallest case design.
Smaller cells can still provide useful battery life, but be sure they are capable of over 1 amp output without significant voltage drop. Higher C cells will produce slightly higher RF output. You may also want a matching JST PH 2.0 socket like this one from AliExpress.
You could try a pre-made protected 18650 battery pack. However, Amazon may not be the best source for high quality 18650 cells; so purchasing 18650 cells elsewhere is recommended if you want the best battery life. You can use protected cells or, you can build your own battery pack with a protection circuit (recommended if you have experience building battery packs using a spot welder).
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Mini micro 3-pin SPDT toggle switch
The battery switch needs to be smaller than is common; I used this one from Amazon which is 8.2mm x 5.1mm and just fits.
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915/868 MHz Antenna
A high-quality hinged dipole fits and works well.
Unfortunately, three out of three different brands I purchased from Amazon did not come close to high quality, and two of the three seemed to be less efficient multi-band antennas.
The one that came with my Station G2 was close, needing only a slightly longer element to bring the resonant frequency down a bit from ~960 MHz. The result looks very good now on the VNA.
The ALFA Network ARS-915P from ROKLAND Should be good quality for US use.
When choosing antennas, be aware of the difference between SMA and RP-SMA. It is, unfortunately, possible to attach an RP-SMA antenna to an SMA jack, but there will be no electrical connection, and you may damage the E22. Always make sure you see a pin on one end or the other when connecting.
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SMA female right-angle 10 or 15cm Pigtail
Like these from Amazon 10cm may not be quite enough for the 2 18650 version of the case.
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Wire
22-24 AWG stranded silicone wire is recommended for power connections to reduce voltage drop and keep RF power output up to spec. 30 AWG silicone wire works well for connecting the optional peripherals.
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Two battery sensing voltage divider resistors
Almost any pair of the same value, axial-lead resistors will work to divide the battery voltage in half so that it can be measured safely by the ADC. 10K - 1M ohm is recommended, as lower values may impact battery life. 1/4 - 1/8 watt will work, but 1/8 watt is easier to fit. 1% recommended, but up to 10% will work. You may need to adjust the ADC multiplier override ratio for accurate battery voltage readings, especially if you don't use 1% tolerance or choose a higher resistance than recommended.
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Common 2.54 mm pin header
These usually come with the NRF52840 board.
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Heat-resistant insulating tape
Every workbench should have a roll of this Stuff. Often called Kapton tape.
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Optional low power GPS module
GPS modules only need power, ground, and two serial connections. This one is relatively low power, fits well and has a small active antenna which fits well in the case.
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Optional passive buzzer/speaker
A passive buzzer can be installed for (quiet) alert sounds and input feedback. These were the lowest profile I could find and they just fit.
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Optional rotary encoder
A small rotary encoder allows control via the Canned Message module. These were the smallest I could find and fits well if the pins are bent carefully.
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Optional 1 inch OLED I2C display
An OLED display is a good compromise with adequate visibility, low cost and reasonably low power. These fit well on the lid of the case.
| E22 Pin Number | E22 Signal | NRF52 Pin | Method |
|---|---|---|---|
| 12 | GND | N/C | No connection |
| 13 | DIO1 | P0.29 | Direct solder |
| 14 | BUSY | P0.02 | Direct solder |
| 15 | NRST | P1.15 | Direct solder |
| 16 | MISO | P1.13 | Direct solder |
| 17 | MOSI | P1.11 | Direct solder |
| 18 | SCK | P1.10 | Direct solder |
| 19 | NSS | P1.09 | Direct solder |
| 11 | GND | GND | Header pin |
| 10 | VCC | B+ | Wire |
| 7 | TXEN | P1.00 | Header pin |
| 6 | RXEN | P0.11 | Header pin |
| NRF52 Pin | Battery sense voltage divider |
|---|---|
| P0.31 | R1 + R2 |
| B+ | R1 |
| GND | R2 |
| Source | Function | Destination |
|---|---|---|
| NRF52 pin B+ | Battery positive | Battery switch common |
| NRF52 pin GND | Ground | Battery negative |
| NRF52 5V USB | 5 volts | Battery switch off |
| Battery switch on | Battery | Battery positive |
| Pin | Function |
|---|---|
| P0.06 | Button Opt |
| P0.08 | Buzzer |
| P0.20 | Rotary B |
| P0.22 | Rotary A |
| P0.24 | Rotary press |
| P1.04 | SDA |
| P1.06 | SCL |
| P1.02 | GPS RX |
| P1.07 | GPS_TX |
Instead of a custom PCB, the castellated edge of the E22 module is soldered on the insulated back of the NRF52 module. Construction time may be 1-2 hours for the basic node or 3-6 hours for a node with a display and 18650 battery pack.
When soldering the castellated edge, be sure not to solder pin 12 of the E22 module. It's an unused ground, and the corresponding pad of the NRF52 module will be used for the battery sense voltage divider.
Strip and tin each wire before soldering it in place.
The OpenSCAD source and STL files are included here. Print the case.stl file for the basic light weight/compact design. Print one of the 18650 files if you plan to use one or two protected 18650 cells for longer battery life. Otherwise, if you want a display, use the display*.stl files. The OpenSCAD source is included if you want to modify the case. If you don't have a 3D printer or a friend with one, some public libraries have them. There are also companies that sell this service.
PLA works great, though PETG or ABS/ASA is better if your node might be left in a vehicle or otherwise exposed to heat. Use your highest strength settings. Supports should not be required. Test fit the cover after printing. It should snap on tightly.
Be sure to perform the initial flash of the firmware on the NRF board before proceeding with the assembly, so that the debug pads on the bottom of the board will be available in case anything goes wrong. This also ensures that the TXEN pad is not driven when it shouldn't be, which could damage the E22.
Follow the Meshtastic instructions to upgrade to the
Adafruit bootloader using
Method 1: UF2.
Download and install the
latest version
of the update nice nano bootloader,
e.g., update-nice_nano_bootloader-0.9.2_nosd.uf2.
If you may later want to use OTA firmware updates, flash the bootloader
included here instead.
Note that since there is no reset button, you need to carefully and briefly short the RST to any convienent GND like the pad next to RST or the USB housing twice within 1/2 second to activate bootloader mode after connecting the USB port to your computer. Be sure you short only the correct pin, 4th from the USB end. A Small tweezers or a stiff wire or even the leads of a multimeter set to measure current works well . It may take more than one try; look for the red LED to remain off or slow "breathing" to show success.
Once the bootloader is installed, you can use the same method to install the Meshtastic firmware. I have provided an older firmware binary, but it is probably best to build the latest firmware using github workflow actions.
Meshtastic does not release pre-compiled firmware for this node, but you don't need to setup a full development environment to build the latest meshtastic firmware. Instead, you can use github workflow actions to build the firmware from your own fork on github. Currently only the develop branch and v2.8.0.* tags include support for this node.
To build the firmware on github:
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Login to your personal github account and go to (meshtastic/firmware)[https://github.com/meshtastic/firmware]
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Create your own fork by selecting "create a new fork" from the "Fork" dropdown menu. Be sure to Uncheck "Copy the develop branch only"
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FYI: Since the github web interface only supports syncing existing branches, if you later want to build a tag or branch that didn't exist when you created the fork, you may need to first delete your fork. This can be done under Settings -> Danger Zone on your github fork. There are ways around this if you are a git command line user.
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Click "Actions" at the top of your new branch main page and enable workflows
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Select "Build One Target" and click on the dropdown "Run workflow" menu
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Click on the "Branch:" dropdown and select the Branch or Tag you wish to build; A stable or beta tag is recommended
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Enter "nrf52_promicro_diy-easypromicro" into the target board field and click "Run workfloww"
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You should eventually see the job status change to "Success" which may take several minutes or even a few hours depending on how busy the github workflow runners are
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Refresh the page in your web browser to show the build job Artifacts
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Download the largest artifact which is a zip file containing .uf2 files for the firmware and factory erase images and an ota zip file.
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Unpack the downloaded zip file and flash the firmware-nrf52-easypromicro*.uf2 file using the same method used to flash the bootloader above.
After everything is succesfully flashed, unplug and plug in just the NRF board into USB power and verify you can pair and connect to it with the Meshtastic app.
If you will connect a battery larger than about 500 mAh, you probably want to short the two square "BOOST" pads on the back of the board near the RST and VCC pads to increase the charge current and reduce charge time; Solder stripped wire-wrap wire, or separate a couple of coarse wire strands, or just bridge the pads with solder, keeping it as thin as you can.
A layer or two of polyimide or other high-temperature tape between the boards is recommended to avoid any chance of shorting exposed vias. Leave the E22 pads on the edge with VCC exposed, but cover the back surface of the pads on the other edge.
Cover the entire pin 12 GND pad next to DI01 on the E22 to avoid any chance of shorts when the resistors are later installed.
After applying and trimming the heat-resistant tape, position the boards back to back, such that pads P0.09-P0.29 on the Pro Micro NRF52840 line up with pads NSS-DI01 (pins 19-13) on the E22. Align the boards carefully such that last eight pads on each board are directly opposite, but not quite touching.
⚠️ Warning: Only seven of the eight aligned pads will be bridged, so the NRF board should overhang the E22 enough that you can see the entirety of each pad on the bottom of the NRF board.
Hold or very gently clamp using rubber bumpers the boards in this position.
If you position the boards carefully, with ~.1mm gap between the inner edges of the pads on the NRF and the castellated edge of the E22, you can make the connections with solder bridges and still easily unsolder them to separate the boards later in case you brick it and need to access the programming pads on the bottom.
If you are manually holding the boards in place, it helps to apply solder to a central pad on both boards before you position them so you can make the first connection with out needing a third hand. After that, you can set the boards down to finish the other six connections.
Start by soldering the two connections on each end, 009 to NSS and 029 to DI01. Solder from the NRF board bottom pad to the edge of the corresponding castellated E22 pad. Before proceeding to solder the 5 remaining connections on this edge of the boards, check that the spacing is correct and that each connection is correct as in the table above.
For battery-powered builds, you will want a voltage divider to sense the battery voltage. Solder a resistor between P0.31 and B+ or RAW and an identical resistor between P0.31 and GND on either side of the board.
To reduce power supply noise, you can also solder a ceramic SMD capacitor between the VCC and GND pads on the E22. Note that while this is best practice in general and the E22 data sheet recommends filter capacitors, it does not specify a required value and it is probably OK to leave this out.
On the other edge of the boards, solder short solid conductors from RXEN to P0.11, from TXEN to P1.00, and from GND to GND. Notice the GND connection is offset by one position so it will be at a slight angle relative to the other pins which are straight across. Insulation is not needed here, but the use of trimmed header pins is recommended. The rigid pins help hold the boards together and reduce the chance of breaking solder connections on the first edge.
Next, we need to connect the E22 VCC; Solder a short length of insulated wire from VCC on the E22 to the B+ or RAW pad.
⚠️ Warning: Never connect USB or power up the E22 without an antenna or 50-ohm load connected, or it may be damaged. And never set SX126X_MAX_POWER define to more than 8 when building firmware for the E22 900M33S, or it will be damaged.
Use a continuity tester to carefully check each soldered connection and also check for any unintended shorts between adjacent pads.
Test fit the board in the case with the USB connector level and inserted into the USB hole. Then, gently press the boards down to seat the edge of the E22 RF shield against the wall in the middle of the case so it can't slide away from the USB hole. If the USB connector won't fit the hole because of filament sag, carefully trim to fit. If the boards won't easily fit down against the wall so that the RF shield is flat against the bottom of the case, carefully remove some material from the wall with a sharp knife or file. If the USB connector is not held firmly in place in the USB hole, add a layer or two of tape to the wall.
Note: If you plan to use this in a 1 or 2 watt output solar node without GPS, you are essentially done with construction of the core part of the node at this point. I don't provide complete build instructions for a solar node here, but you may want to review the remainder of this document for configuration and other useful information. A 1 watt output solar node could be powered by a protected Li battery connected directly to the B+ or raw pad and charged by a 5 volt regulated panel connected to the USB port or the LDO pin mentioned in section 15. Or, a 2 W node could be constructed by connecting the 5 volt output of a more efficient MPPT charge controller with battery to B+ or raw.
Clip all three terminals of the battery switch so they are a bit shorter than the original length of the outside two terminals, and test fit it in the case.
Solder wires to the two farthest terminals, closest to the SMA.
Use a nut or a few washers inside the case to adjust the exposed length of the SMA jack so that the antenna fits properly. Tighten the nut snugly while holding the jack so the pigtail touches the bottom of the case where it connects to the SMA jack to allow room for the battery switch. Test fit the antenna; it should get tight just before it reaches the nut. If it contacts the nut first, adjust the inside spacing.
Carefully connect the pigtail U.FL to the E22, and be careful not to pull or twist it off during the remainder of the assembly.
Never power up the E22 or connect the USB without an antenna or load connected or it may be damaged.
As you make the remaining connections, place the boards and battery switch in position and trim wires close to the required length so they will fit neatly in the case.
Solder the wire on the battery switch terminal closest to the SMA to one of the LDO terminals, which are connected to the USB VBUS pads (You can leave this off if you don't want the option of higher power.) Unfortunately, USB power is not connected to a pad on this board. But, it is easy to use a continuity tester to find a convenient LDO pin that connects to the USB power pins. The USB VBUS pads are the larger pads second from either end of the USB connector.
Move the battery switch toggle to the off position, closest to the case.
Connect the wire from the middle battery switch terminal to the B+ or raw pad, or to the VCC pads of the E22.
If you don't have a jack to fit the battery connector, and you don't need the battery charger that may have come with the battery, you can use its jack and wire for the battery connection. Or, you may carefully solder the battery lead directly if you don't want the battery to be removable.
Connect the remaining (closest) battery switch terminal to the positive (red) battery lead or the correct battery jack wire.
If you purchase a protected 1S2P battery, you may need to remove or reform the heat shrink wrapper to use the existing case design which is intended to fit the cylindrical cells.
If you have access to a battery spot welder (soldering directly to 18650 cells is not recommended), you can build your own high capacity 3.7 volt 18650 1S 2P pack for a more reliable connection than the removable cell method below. Be sure to include a battery protection board if you use unprotected cells.
Insulate the positive terminals with paper disks or heat resistant tape before spot welding .2mm Nickel strips on both ends; positive to positive and negative to negative to form a 1S 2P pack. Be sure to keep the cells perfectly parallel to each other with no gap as the case does not have extra room. Use additional heat resistant tape where the positive terminals of the protection circuit will go.
Solder the wires to the battery protection circuit before welding its tabs over the top of the welded Nickel strips. Observe correct polarity everywhere.
This method can be fiddly and less reliable than a protected battery pack with a connector as above especially if the node is left in a hot environment, but it uses easy to find protected cells and requires no battery pack construction.
Fashion battery holder contact pads from a thin piece of shiny metal which will take solder. I cut small pieces of .2mm Nickel battery welding strip, but a piece cut from the lid of a tin can might also work.
Once you determine where the contact pads will be mounted, test fit the pads with the battery. Solder wire to each contact pad in a location where it will not get caught when the battery is installed. You can use double sided adhesive foam mounting tape to mount the battery contact pads in the battery holder section of the case.
When installing the battery for the first time, work slowly to allow the foam tape to compress and be careful not to apply too much pressure at the negative contact wall; this part is easy to snap off. If the battery does not fit snugly, add a second layer of mounting tape. If it is too tight, use less mounting tape. If the battery does not make solid electrical contact at the negative side, you can add a bit of solder to create a bump near the middle.
Connect the remaining (closest) battery switch terminal to the positive contact pad at the switch end of the case.
Tighten the battery switch nut snugly while preventing the switch from rotating.
The off position of the battery switch is towards the case, and the on position is towards the SMA jack. Note, however, that the node will also be powered on when the switch is off if USB power is connected.
Check that the battery switch is in the off position and that the antenna and U.FL are still connected.
Solder the negative (black) lead of the battery, contact, or jack wire to a GND pad.
If you used a connector for the battery, connect it. Arrange wires and place the battery in the case. Hints for 18650 cells: Install the one on the longest side first. It may be easier to insert the positive end of cells first. Observe battery polarity, there is no reverse voltage protection!
When used with a mobile device, no GPS is needed as the mobile device can be configured to provide it's location. If, however, you want to use this node as a tracker, a GPS can easily be added.
The NRF52840 dev module includes a switched 3.3V power output which we take advantage of to extend battery life by powering the GPS module only when needed. When the GPS is enabled, battery life will be reduced, especially inside buildings where a fix is harder to obtain. You can still expect the battery recommended here to last a full day.
If you use the recommended GPS module or one with the same form factor and pin out, you can connect the Rx and Tx pads via header pins and use wires only for power and ground. If you use a different GPS module, be sure to connect Rx to Tx and Tx to Rx.
First, solder two header pins, long side down to the P1.02 and P1.07 thru holes on the NRF52840 module and then remove the plastic spacers.
Trim the pins to fit the GPS module and place it on the pins with it's metal shield flat against the NRF chip as shown.
Solder the GPS module in place and solder wires to connect the 3.3V and GND pads from the NRF52840 module to the GPS module as shown.
Insulate the back and sides of the GPS antenna with tape and connect the U.FL. Position it in the case as far away from the other boards as possible so that it faces up and away from obstructions. If you attach it with double sided tape to the exposed portion of the E22 module, the extra ground plane may help with reception.
The buzzer leads can be soldered directly to the output, P0.08 (+) and a ground. If you bend the negative pin, it can be soldered directly to the USB connector housing; providing ground, correct placement and a good mechanical attachment.
Solder 4 short light gauge wires from the appropriate display module pads to ground, B+/raw, P1.04 (SDA), and P1.06 (SCL). Power on and test the display, then carefully place it in position on the corner pegs on the inside of the lid with the top of the display towards the longest edge.
Tape the display in place from the back with heat resistant tape, being sure to cover the heat steaks. Then while holding the display in place, carefully apply heat with a very low temperature flat soldering tip to melt the corner heat stake pegs and fasten the display to the lid.
Carefully bend the pins over the back of the plastic encoder body so as to keep the pins where they exit the plastic as tight as possible to allow them to fit in the case.
Strip a longer than normal portion of a short light gauge wire and solder it from one pin on the 2 pin side to the middle pin on the 3 pin side and continuing on to a ground pad on the NRF or E22 module.
Solder a wire from the remaining pin on the 2 pin side to P0.24. Solder two wires from the remaining pins on the 3 pin side to P0.20 (B) and P0.22 (A).
Ensure no pins are shorted except the two ground pins and cover the back of the rotary encoder with tape.
Install the rotary encoder as shown above.
Enable the Canned Message module with Rotary encoder #1 enabled and GPIO pin 22 and 20 for the A port and B port and GPIO pin 24 for the Press port.
If you haven't already, slide the board assembly fully into place.
Carefully install the case lid, taking care not to pinch wires. You may want to use some tape to keep the longer wires in place at the side of the case, away from the protruding parts of the lid.
In addition to the normal Region and LoRa preset, some hardware features of this node need to be setup after the initial firmware flash using the CLI or Meshtastic phone app:
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Voltage sense: Device configuration -> Power -> ADC multiplier override ratio
For the recommended 10K to 1M ohm resistors, 2.0 should be close; for a more accurate reading, let the reported voltage stabilize for several minutes, then measure the battery voltage with a multi-meter and calculate a new ratio as current_ratio * measured_voltage / reported_voltage
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Optional GPS: Device configuration -> Position -> Device GPS -> GPS Mode
Set to "ENABLED" if you wish to use your GPS or "DISABLED" to save power
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Optional display and rotary encoder: Module configuration -> Canned Message
Turn on "Rotary encoder #1 enabled"
Set "GPIO pin for rotary encoder A port" to 22
Set "GPIO pin for rotary encoder B port" to 20
Set "GPIO pin for rotary encoder Press port" to 24
Set "Generate input event on Press" to "SELECT"
Set "Generate input event on CW" to "RIGHT"
Set "Generate input event on CCW" to "LEFT"
After saving the rotary encoder configuration, use the rotary encoder and display to select the "System" page, press the encoder and set "Notifications" to "Notifications" or anything other than "All enabled"; this will improve response time for the encoder by disabling buzzer sounds when the encoder is rotated.
If built as described here, this node can be powered by either USB or the internal 1 S Lithium battery.
When the battery switch is on (towards the SMA jack), the battery is connected to both the battery terminal of the NRF board and VCC of the E22. If the USB port is plugged in when the battery switch is on, the onboard charger will charge a 1000 mAh battery in about 3 hours, assuming you shorted the square pads as suggested.
When the battery switch is off (towards the case), the battery is completely disconnected, and the USB voltage is connected to the B+ pad and VCC of the E22. This means that the battery will not charge with the switch off, and that the node will operate only from USB power.
| Battery Switch | USB Power | Node On | Charging | TX Power |
|---|---|---|---|---|
| On | Connected | ✅ | ✅ | ~1 watt |
| Off | Connected | ✅ | ❌ | ~2 watts |
| On | Not connected | ✅ | ❌ | ~1 watt |
| Off | Not connected | ❌ | ❌ | none |
⚠️ Warning: The antenna MUST be connected anytime USB power is connected or the battery switch is on, including when charging, to avoid damaging the E22 module.
When the antenna is installed, it helps protect the battery switch from being inadvertently changed. The 3D design files include an optional safety device which, when screwed onto the SMA jack, will prevent the battery switch from accidentally being turned on. Use this in case you wish to carry the node with the antenna detached. If you really must charge the battery without an antenna connected, connect a 50-ohm load.
When operating on battery power, the voltage supplied to the E22 module is between 4.2 and 3.0 volts. The maximum output power of the E22-900M33S will vary from about 1.2W to about 0.5W as the battery voltage drops.
When operating on 5-volt USB power with the battery switch off, the E22-900m33S is
capable of a maximum output power of about 2 watts. The Meshtastic firmware
variant easy-nrf-pro-micro_e22 is configured to expect battery
voltage, thus, when powered via 5-volt USB, configuring the node for 30 dBm
(1 watt) output should produce about 33 dBm (2 watts).
Because they are designed for higher current applications, many cheap battery protection boards are set to cut off at less than the safe minimum of 3.0 volts. To avoid damaging your battery or reducing its service life, it is recommended to monitor the battery voltage and turn off or charge your node before the battery is exhausted.
When charging, the blue LED will remain lit until the battery is 80-90% charged. Then it will cycle on and off at various intervals while the charge is completed and maintained.
When running from battery power, the red LED closest to the USB connector will periodically flash very briefly. When running from USB power, it will flash every 2 seconds.
If you installed and enabled the GPS, its LED will light while looking for a fix. It will flash at 1 Hz when a fix is obtained and turn off when when idle. Note that when the GPS is configured as "not present", the power will remain on, but no fix will be used. If you install a GPS, be sure to enable or disable it.
This style of construction can also be used in a solar node. The E22 ground plane does reduce the Bluetooth range and makes it more directional which is usually not a problem for a pocket node, but if you need to update a solar node OTA, you may want to remove the red chip antenna and solder the coax to an external antenna in it's place. Note that the second pad which the chip antenna is soldered to is not a ground, so you will need to find another ground, perhaps by carefully removing some solder mask from the ground plane in a convenient location.
When used with a solar power manager which provides a 2 amp 5 volt regulated output, you can connect it to the B+ pad. In this case wire the resistor voltage divider to the lithium battery positive terminal instead of the B+ pad.
A big thank-you to Bob Van Valzah for testing the node and reviewing and improving this document!