The main advantage of the TinkerSend-Mobile board is that you can avoid having to build and operate your own base station while still being able to operate independent of any WiFi network. This is a great option if your rover is going to be operating in remote areas. As long as you have reception on the 4G network of your choice, you can receive RTK correction data.
Mobile Data and RTK Correction Data Sources
Subscriptions that support mobile data are remarkably inexpensive. We use the Tello 1GB per month data subscription, which currently costs $6 per month and a 2 GB subscription costs $10 per month. Continuosuly downloading RTCM correction data at 1 Hz takes about 60 MB per day, or 1.5 GB per month. In most cases it is not necessary to download RTCM data continuously, so one of these inexpensive plans is more than sufficient for data.
Free public sources of RTK correction data vary considerably around the world. RTK2GO may provide correction data in your area (see this map), in the western united states UNAVCO has good coverage, or state and federal governments in other locations may provide correction data. There are also paid subscription services for correction data via NTRIP Casters. Note that some correction services provide L1/L2 corrections, which do not fully support the PX1125R L1/L5 bands.
TinkerSend-Mobile is built around the SIM7000G module from SIMCom and uses the same RT6154A power supply as the TinkerNav base board. A separate power supply and larger capacitors are needed for TinkerSend-Mobile since the transmit cycle of the SIM7000G requires 2 amps and also a slightly different voltage of 3.8 volts, vs 3.3 volts for TinkerNav. TinkerSend-Mobile draws its power from the VCC pin on TinkerNav, which can be between 1.8V and 5.5V. A total of 500 uF of capacitance is provided after the power supply, with 300 uF near the power input for the SIM7000G.
Only 4 logic pins are needed to communicate to TinkerSend-Mobile; transmit and receive pins plus a power key, and reset pin. The power key must be cycled after the board is powered before it will begin operating. This is normally done by the RP2040 through the power key pin, but a physical button is also provided for the power key if needed. The reset pin resets the SIM7000G. A RS0102YH8 level shifter is used to translate logic signals from the RP2040, which are at 3.3V, to the required 1.8V logic level for the SIM7000G.
TinkerSend-Mobile has two status LEDs, a status LED on the left side and a network LED on the right side. The LEDs operate as follows:
On indicates that the device is powered and ready.
- Blinking 64 ms on; 800 ms off: No registered network
- Blinking 64 ms on; 3000 ms off: Registered network
- Blinking 64 ms on; 300 ms off: Data transmit
- Off; Power off or PSM mode
There are U.FL inputs for both a main antenna (left top) and a GNSS receiver (top right)
Schematics and KiCad Files
The TinkerSend-Mobile is built to run connected to the TinkerNav base board, but is also breadboard compatible. The diagram below shows the pinout for the TinkerSend-Mobile board.
See our TinkerSend Mobile <Getting Started> page for example software.