There is now a Moteino 8Mhz variant. This has no LDO and hence allows to harvest the lowest power modes from the Atmega328p MCU. It has the following differences to the regular Moteino:
- no LDO linear regulator
- the VIN and 3v3 pins are connected by a 0ohm resistor (bridge)
- must be powered from 3.6v or less when RFM radio and/or FLASH-MEM are installed. The RFM radio and FLASH-MEM are damaged by 5V. Without these components the board will work up to 5V.
- 16mhz resonator is still installed but not used with the 8Mhz fuses. This means you can change the fuses yourself and run the board at 16Mhz it if you’d like, but this will only be safe down to about 3.3V
- fuses are: LOW: 0xD2, HI: 0xDC, EXTENDED: 0xFE
- even more ultra low power – 2uA less current than the regular Moteino
- runs DualOptiboot compiled for 8mhz
- 57600baud upload programming speed (vs. 115200)
- you will need to install the latest Moteino definition (v1.3 or newer) in your Arduino IDE Board Manager to gain the new Moteino (8Mhz) target board:
These types of Moteinos are ideal for ultra low power coin cell and other micro power powered nodes – power them from 3.6V or less. Of course, when you have such tiny power supplies, you must choose your transceiver carefully, as you likely cannot transmit at full 20dBm power from a tiny coincell. The W/CW 13dBm radios running the auto-power-dial RFM69_ATC library extension would be recommended for running on coin cells or small solar cells.
To program this Moteino the FTDI-Adapter offered in the shop can be modified to pass a safe 3.3V to the 8Mhz LDO-less Moteino – cut the *5V Output Voltage jumper and solder the 3.3V one:
Alternatively, you can build a dedicated adapter that takes the 5V from the USB and regulates it to 3.3v, here’s such an example which uses the LDO from the Moteino itself (MCP1703) along with a 1uF and 0.1uF caps, all other connections are passed through and assumed to be 3.3v levels:
You would then use it in between your stock unmodified FTDI-Adapter (or equivalent board, providing 5V VIN power and 3.3V TX/RX/DTR signals), and the no-LDO Moteino which requires 3.3V when radio/flash are present: