IOT version.

Communicates through a nRF24 module with my raspberry pi server. The server is running the nRF24_MQTT bridge.

Install platformio, then:

$ pio run -t upload -t monitor

You can turn on UART prints in the platformio.ini file to see what's going on.

build_flags =
	; Debug prints on UART: 0 = None (fastest!) 1 = Some, 2 = A lot
	-DDEBUG_LEVEL=2

a little more info on the hardware can be found in this old blog post.

• A large jam jar (Ikea)
• Mini USB Nano V3.0 ATmega328 5V Microcontroller Board (eBay)
• FTDI serial cable for flashing (eBay)
• Solar cell, 5.5 V, 50 mA or larger (eBay)
• Lipo - battery cell, 100 mAh - 600 mAh (eBay / old laptop / old cellphone, etc.)
• 12 x tiny LEDs, different colors, the smaller the better, with ~80 - 200 Ohm series resistors, depending on how bright you want it (kit from eBay)
• Very thin magnet wire from the coil of a miniature relais
• SMD resistors with 1 % tolerance: 2 x 560 kOhm, 2 x 160 kOhm. For two voltage dividers to sample the solar cell and battery voltage
• SMD ceramic capacitors, 2 x 100 nF, to stabilize the analog inputs of the AVR
• Some circuit board, glue, prototyping wires, sticky tape

The AVR board has been modified in the following way for very low power operation:

• The voltage regulator has been removed and VCC has been connected directly to the battery
• The Schottky diode, which is already on the board, has been rewired to be in series with the solar cell. It only has 0.2 V forward voltage drop, which is excellent!
• 2 Voltage dividers with the 560k and 160k resistors and 100nF capacitors have been made and connected to Vsolar and Vbattery. The AVR uses the internal 1.1 V reference voltage for the ADC, which allows to measure voltages up to 4.95 V

The fuses have been reprogrammed to use the 8 MHz internal oscillator instead of the 16 MHz onboard crystal. This significantly speeds up the processor wake up time from sleep and hence saves power.

Buspirate connection

Check current fuse settings:

cd ~/.platformio/packages/tool-avrdude
./avrdude -C avrdude.conf -p m328p -c buspirate -P /dev/ttyUSB0

AVR Fuse Calculator

Switch to 8 MHz internal oscillator

• no startup delay
• with 1.8 V brown out reset
• flash the bootloader for 8 MHz (only needed if previously running at 16 MHz)

# to use bus-pirate, uncomment the upload_flags and upload_command
# overrides in platformio.ini
pio run -t bootloader

Note that this pinout allows to connect an optional nRF24 module to PORTB.

Silkscreen, Firmw. Ch.    AVR               (*) = on LED board
2,          6             PD2   LED   y      *  + GND pin
3,          7             PD3   LED   o      *
4,          8             PD4   LED   r      *
5,          9             PD5   LED   w      *
6,          10            PD6.  Led   g      *
7,          11            PD7.  Led   b      *
8                         PB0   Rf ce        *   (No LED)
9                         PB1   Rf irq       *   (No LED)
--------------------------------------------
10                        PB2   Rf csn
11                        PB3.  Rf Mosi
12                        PB4.  Rf Miso
13                        PB5.  Rf Sck
A0,         0             PC0   LED   w      *
A1,         1             PC1   LED   r      *
A2,         2             PC2   LED   y      *
A3,         3             PC3   LED   g      *
A4,         4             PC4   led   w      *
A5,         5             PC5   led   b      *
A6                        ADC6  Vbatt
A7                        ADC7  Vsolar