The first of the main PCBs has now been soldered up and is ready for testing. This is happening a lot later than we’d have liked due to supply chain issues. However, the initial testing of the power supplies seems to be positive.
Category Archives: Technology
First custom designed sensor
This project has required the design and development of several custom sensors. This is the first one to have been built. It uses 5 one-wire temperature sensors attached to an AVR. The AVR then runs code to interface with the sensors. In order to connect to the main sensor node the AVR uses RS-485. This means that it can be away from the main node, and because of the multi-drop nature of RS-485 multiple such devices could be attached. The other sensor nodes also interface using RS-485 so each node could have different types of remote sensor attached.
CC1120 Contiki port
The first batch of PCBs to be used in the project have been created. These boards will take a 12V input and give a 5V 2A output. These will be useful for powering devices in the first tests that are carried out. There are a few more boards on the way including 5V 250mA boards, which will also be used for testing and powering external peripherals.
Range testing 868MHz radio links
I just did a quick range test with the CC1120 transceivers (our favourite for range):
at 2.2km it is easy to link even with omni antennas (-99dB) but a yagi was excellent (-89dB).
At 3.3km (not in good line of sight and grazing wet ground) Yagi to omni was starting to loose packets (-106dB) and yagi to panel antenna was not much better but still communicating. This bodes well for a low power 868MHz network over the whole field site including our 3km link up from the valley.
This was at 50kbit/s using the CC1120DK TI test boards.
big round Omni was 4dBi gain
Yagi tested was 9 dBi gain
Panel was 7dBi gain