Generally, if we purchase 2 identical sensors, they will have identical addresses, so we can only use 1 of these at a time. Some models might require reprogramming the module to change the address, which isn't practical. But other sensors sometimes offer simple ways to set the address.
For example, from Supported Sensors and Inputs, a few temp sensors that are integrated are:
- Digital Matter Temperature Probe
- This sensor can be given 1 of 2 unique addresses by connecting the green wire to either 3V3 or GND (see Falcon - Wiring in DM I2C Sensors) So we can use 2 of these at once
- Digital Matter Temp/Hum Sensor
- This sensor has 1 fixed address, so we can only use 1 at a time
- TMP117 Temp Sensor
- This temp sensor (comes as a chip) - can be given 1 of 4 addresses by jumping pins on the module. So we can use 4 at a time
Equally we could use all of these together, i.e. 2 x Temp Probes + 1 x Temp/Hum Sensor + 4 x TMP117. Given all 7 have unique I2C addresses.
Other Limitations
While we can theoretically be connecting up to 128 sensors to a Eagle, we run into some other limitations that mean in practice we wouldn't really do this.
- I2C stands for Inter-Integrated Circuit - it was designed for low speed communication between components on a circuit board. So it does not work well for long cable runs over a few metres
- Simply attaching lots of sensors is going to become impractical
- There are only 14 available analogue data fields currently on the device to store any sensor readings. So 14 is our upper limit. However if we are approaching this we should consider BLE sensor options.
However it should be noted that for Telematics Guru users, generic tag temp data readings from the tag list data are not integrated - so generic BLE sensors we connect to the Eagle will not be able to have their temp data displayed in TG currently. For the SensorNode BLE, 2 can be used per Eagle on TG . See Connecting a SensorNode Bluetooth® to an Eagle, G120 or Remora2.
When both external power and batteries are installed, the device will use whatever is supplying the higher voltage.
This will prevent set such as installing 4 x LTC batteries (giving ~14V) in conjunction with a 5V external supply. The batteries will always be used in this configuration
When external and battery supplies are used, if there is a power cut, we swap over to batteries, and some capacity is used until external power is restored.
The Eagle uses an internal sticker antenna with a UFL connector, which is attached to the inside of the housing and the UFL connected to the PCB.
If an external antenna is desired, the user can drill a hole in the housing, install a UFL to SMA pigtail, and then connect an external antenna.