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What is it?
This is Grasshopper, a small (0.71 " x 1.76") development board with Murata's CMWX1ZZABZ-078 FCC certified module containing ST Microelectronics' STM32L082 32 MHz Cortex M0+ MCU with 192 kByte of flash and 20 kBytes of RAM and Sematech's SX1276 LoRa radio. The development board exposes 19 GPIOs to the user as well as 3V3, GND, VIN, and VREF (for the analog sector), has an indicator led on GPIO 13 as well as a power-on led that can be disabled via a solder jumper for lowest power usage, and has an on-board antenna suitable for either 868 or 915 MHz.
In fact, the chip antenna is tuned for a wide band (858 - 928 MHz) which allows the SX1276 LoRa radio to be used in a surprisingly large number of regions of the world including:
- Asia AS923
- Australia AU915
- Europe EU868
- India IN865
- Korea KR920
- US US915 (64 + 8 channels)
The Grasshopper development board is intended to be programmed using an Arduino IDE (just like Ladybug, Butterfly, and Dragonfly, flashing new programs and receiving serial output through the microB USB connector. But we have exposed the SWD port as well for those users who prefer to use traditional tool chains and debuggers.
We have extended our successful STM32L4 Arduino core to the Grasshopper STM32L082 variant to allow all of the usual serial protocols and peripheral utilities expected for an Arduino-programmable development board. First drop of the (alpha) STM32L0 Arduino core is reposited [here](https://github.com/GrumpyOldPizza/ArduinoCore-stm32l0). We have a GitHub repository of Arduino sketches that run on the Grasshopper here. Here(adapted from Simon Levi's LadybugFC tutorial) is how to get started if you are new to Arduino or have forgotten how to set it up.
The board can be powered from the USB connector or from a 1S LiPo battery (3.5 < VIN < 5.5 V). There is a JST port for connecting a LiPo or power may be applied to VIN and GND on the board edge. The Grasshopper LoRa development board uses an NCV8170 3V3 LDO with 150 mA output for power management. This LDO has a quiescent current of just 500 nA allowing the ultra-low potential of LoRa to be realized in this design. When the power-on led is disabled (cut the trace between solder pads on the back), the Grasshopper uses just 2.1 uA in STOP mode with full data and state retention. The LoRaWAN radio API is designed to keep the MCU in stop mode as long as possible. Proper construction of your Arduino sketch will allow the Grasshopper plus sensor add-ons to last for months on a small LiPo battery.
This test has the Grasshopper blinking the built-in led for 100 ms and then stopping for 5 seconds. The average current is roughly proportional to chosen clock speed. Click here for more discussion in Hackaday.
Initial tests show reception out to 150 meters with no direct line of sight (through houses and cars, etc) and >500 meters out in the open. One report shows reception at a 30 meter tower antenna 1.4 km away with RSSI -115 and SNR of -9. This is pretty good performance for this simple pcb antenna! We have added an u.Fl connector so even longer-range can be achieved with an external antenna.
Why did you make it?
BLE and wifi are great and each has its niche. BLE requires low average power (~ 1 mA) and is great for streaming small amounts of data (~1 kByte per second) at short range (<10 meters), while wifi can stream large amounts of data (100s of kBytes per second) at relatively longer range (~100 meters) but at much larger power budgets (10s of mA). LoRa promises the best of both worlds, offering ultra-low power usage (< 1 mA average power) and ultra-long range (> 1 km).
We wanted to get started in this wonderful new radio sector and what better way than with Murata's new LoRa radio module, which offers a compact and complete solution that doesn't require an external antenna and allows a super small development board perfect for remote applications and even for wearable use!