WiNode is
the first standalone wireless sensor device from Nanode Ltd. It is aimed at wireless sensing and control
applications, and has a number of features not found on other devices. WiNode
can form part of smart wireless sensor networks and be used in conjunction with
a Wireless - Ethernet gateway such as Nanode RF.
Main
Features
ATmega328
with RFM12B wireless transceiver operating at 433MHz or 868MHz
Motor driver
IC for driving 2 dc motors, 4 relays or even a loudspeaker. Accessible via
screw terminals.
4 general
purpose analogue inputs with voltage scaling networks. Accessible via screw
terminals.
Could be
used for current transformers or opto-reflective pulse counters (gas meter).
microSD card
– for datalogging or file storage. Can be used to store audio files for
playback via loudspeaker.
32K battery
backed SRAM – retains data during a power outage
Real Time
Clock and Calendar with alarm wake-up function
At the core
of Winode is the combination of the Atmel ATmega328 microcontroller and the
Hope RF RFM12B wireless module. This is a tried and tested pair, used in
designs by JeeLabs and Open Energy Monitor.
The code library to support the RFM12 is that written for the Jeenode –
so ensuring 100% compatibility.
The new
WiNode 4.0 design corrects a number of shortfalls in the earlier version and
offers a compact yet versatile platform for wireless sensor application
development.
WiNode is
built on a compact 58mm x 66mm (2.3” x 2.6”) pcb, and retains the Arduino style
shield connectors, allowing expansion by means of Arduino shields. However 100%
compatibility cannot be guaranteed as WiNode uses several of the digital I/O
pins for its own purposes. However for those wishing to add circuitry to
WiNode, a prototyping shield on extended pin headers works well.
WiNode
offers several additional hardware functions, not generally found on other Arduino-like
platforms. These offer a range of functions considered to be useful to typical wireless
sensor, actuator and control applications.
External Connections
Along the
right hand edge of the pcb is a strip of 10 screw terminals. This is where most of the interfacing to
sensors and actuators would be made using simple wired connections. These screw terminals offer four analogue
inputs and four high current (2A max) motor or relay drivers.
Motor Drives
The WiNode
has an on-board dual H-bridge motor driver – which can be driven with PWM for
driving inductive loads such as motors relays, solenoids and even loudspeakers
for audio applications. Up to four
relays, two reversing small dc motors or one stepper motor can be connected to
these outputs. The motor drive outputs
are marked M1 – M4 on the underside of the pcb.
The motor drive channels are Digital 5, Digital 6, Digital 10 and
Digital 11 – however restrictions apply on D 10 and D11 when accessing devices on
the SPI bus.
Relays and
solenoids can be driven, allowing the possibility of using WiNode for
applications such as a wireless central heating controller, garden irrigation
system, or solar PV monitoring system.
The dc motor outputs, used in conjunction with analogue inputs would
allow WiNode to form the basis of a two-axis PV tracking controller – using dc
motors for drive and potentiometers to read off the position.
Analogue
Inputs
The analogue
inputs are fitted with 10K input resistors, and a choice of potential divider
resistor array. Using the 4K7 array
provided allows voltages up to 10.32V to be measured – or almost exactly 10mV
per ADC count. Fitting a 3.3K resistor
array allows up to 13.3V to be read – making WiNode compatible with 12V battery
systems. The choice of this resistor
array is left to the individual user, if the array is omitted, the analogue
inputs will have a full scale of 3.3V – as WiNode operates at 3V3. The analogue
input terminals are marked AI0 – AI3 on the underside of the pcb. Analogue inputs AI0 and AI1 have 160Hz low pass filters fitted (10K
and 100nF) to reduce noise and transients. These may be omitted if not needed
or if fast ADC sampling is required.
Power Supply
The screw
terminals also provide connection to the power supply. This allows a dc supply
of up to 12V to be connected. If
operating at 12V, the 7805 voltage regulator should be fitted with a heatsink –
as should the 754410 motor driver IC. The external voltage input is marked Vin
and 0V on the underside of the pcb.
If an unregulated
external dc power supply is not desired, WiNode may be powered from a nominal
5V supply (eg USB) via pins 1 (0V) and 3 (+5V) of the 6 pin FTDI header. This
supply is further regulated down to 3V3 to power the whole pcb – so WiNode could
be powered from a small solar panel with a nominal 5V 250mA output.
Real Time
Clock
WiNode is
fitted with a Microchip MCP79411 real time clock/calendar. This is a small 8 pin surface mount package
soldered to the underside of the pcb. The MCP79411 also contains an EEprom area
where non volatile data such as Node ID, MAC address etc could be stored. The MCP79411 also has an “alarm” output which
can be used to generate a wake up interrupt or regular square wave output –
interrupting the microcontroller on Digital input 3. The WiNode pcb also allows a DIP version of
the Dallas/Maxim DS1307 RTC to be fitted as an alternative to the MCP79411. The RTC is battery backed by a 0.22F supercapacitor.
32K External
SRAM
This is a
static RAM connected to the microcontroller via the SPI bus. It can be chip selected using Digital output
8. The supercapacitor provides battery
backup for this device. The SRAM can be
used for applications requiring temporary storage of moderate amounts of data,
such as an audio sampling buffer (4 seconds of audio at 8kHz sampling frequency),
or for short term datalogging. The SRAM
can also be used for program storage if the WiNode is programmed using Arduino
TinyBASIC. Library routines to make the most of this external SRAM are
currently under development.
Micro SD
card
For
applications requiring datalogging, or accessing files, a microSD socket has
been included on the underside of the pcb.
One recent application of WiNode was as a programmable sound generator, where
audio files were stored in the SD card, and played back through a loudspeaker,
driven by one half of the motor driver H-bridge IC. If this option is desired,
then additional 10uF electrolytic capacitors and 1 ohm resistors should be
fitted to provide low pass filtering of the audio output.
Unfortunately,
due to hardware restrictions, motor output 3 is not available when writing data
to the SD card.
Summary of
I/O Usage on WiNode 4
Dig 0 Serial Rx
to FTDI header
Dig 1 Serial Tx
to FTDI header
Dig 2 Interrupt from RFM12 wireless transceiver
Dig 3 Interrupt from RTC square wave or alarm wakeup
Dig 4 microSD chip select
Dig 5 PWM_2 output (M2) from motor drive IC
Dig 6 PWM_1 output (M1) from motor drive IC - Green LED
Dig 7 Enable line for motor drive IC – held normally
low to inhibit drive.
Dig 8 Chip select line for 32K SRAM
Dig 9 Unused
Dig 10 Chip select line for RFM12B wireless
transceiver – also motor PWM_4 (M4)
Dig 11 MOSI signal for SPI bus – also motor PWM_3 (M3)
Dig 12 MISO signal for SPI bus
Dig 13 SCLK signal for SPI bus
AN0 Analogue input 0 (filtered)
AN1 Analogue input 1 (filtered)
AN2 Analogue input 2
AN3 Analogue input 3
AN4 I2C data (SDA) for Real Time Clock
AN5 I2C clock (SCL) for Real Time Clock
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