Nodes
Sensor nodes, typically consist of some combination of
- An off the shelf development board (aka dev-board) which includes communications (WiFi, LoRaWan, or GSM)
- One or more sensors for example for temperature & humidity, or light
- One or more actuators - such as a relay or a light
- A way to power them
- An enclosure (box) of some sort.
For example this simple node, consists of:
- a D1 Mini Pro dev board with an ESP8266 processor and WiFi (~€2.80)
- An SHT30 temperature and humidity sensor (€2-3)
- A cable that plugs into a USB power supply
- In a cheap ABS box €0.35
So overall cost about €6
A more detailed list of supported hardware has its own page; but in summary.
We have focused on two processors - ESP32 for power; or ESP8266 for price. Both come in a range of options, and our preference so far has been those in the D1 format as it makes development of sensors cheaper. The code is also running on a Wvroom at Kopernik, and is expected to port fairly easily to any board with built in WiFi.
Sensors are added, typically these either use one of the encoded interfaces (I2C or OneWire) or are attached to an Analog or Digital pin. We currently support several Temperature & Humidity sensors (SHT30; DHT11; DHT22); Capacitive Soil Sensors; Light Sensor (BH17550); and generalized analog or digital devices or buttons. These sensors are sending results via MQTT to other devices via the cloud.
Actuators do something - they may or may not be required in any system, but the most common is a relay which is supported. Monochrome LEDs are currently supported with RGB LEDs to come soon.
Some off the shelf consumer hardware is easily re-programmable, and so the devices can easily be included in the Frugal IoT system, and appear on dashboards etc. A couple of examples are:
The Sonoff is a simple relay for mains power, and is easily reprogrammed .
A combination temperature / humidity / light / soil sensor with a couple of buttons, and a motor control. We can program it, and replace most of the functionality. More details to come.
Any node can also run control software, or this can be on a separate node. There is currently basic support for a control, which incorporates hysterisis to avoid lamps etc flashing on and off near the set-point.
The trick with getting cost down, is always to use an existing enclosure - one can see, for example with the LilyGo Higrow where a small 3D printed case costs €7. At the moment we are using any of a range of ABS boxes, ABS is in the middle in terms of UV stability, so alternatives may be preferable for exposed situations with a long lifetime expectancy. These boxes typically run under €0.50 so can be replaced if required. The goal is to minimize work needed to them - our favorite design just cuts a couple of notches with a sharp knife for cable in/out, and (if required) drills a hole for the antenna.
There are four likely communications modes for nodes.
- WiFi - either to an existing network, or bridged to the cloud via a WiFi/GSM Modem.
- LoRaWan - via a Lora/GSM gateway
- GSM
- Offline - data transfer via SD card
WiFi is build into many dev boards and has been used for early tests.
LoRa is more reliable, uses less power, and has longer range, however the gateways are expensive - from €200-600 so can only be justified for projects over a wide range with lots of sensors.
GSM may be appropriate for remote single sensors, but has not been tested yet.
SD card storage is under development, but not complete yet.