Would a sensor like this kill battery life on a Ruuvi tag? Or is this something we could put on the wishlist for 2022?
PT
SCD41 is a very interesting sensor, however the minimum voltage of 2.4 V and peak current of > 100 mA aren’t a good fit for a coin cell battery.
It would work better as a add-on to Ruuvi Gateway, as there’s USB power available
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Yes, not many coincell driven co2 sensors out there.
I’m for the moment testing a japanese co2 beacon sensor BLE Sensor Kanki AirMier – obniz store that also have 5v from usb.
Since the spec sheet of Sensirion SCD40 (https://sensirion.com/media/documents/C4B87CE6/627C2DCD/CD_DS_SCD40_SCD41_Datasheet_D1.pdf) also contains this:
Average supply current for low power periodic measurement IDD:
VDD = 3.3 V typical 3.2 mA, max 3.5 mA
VDD = 5 V typical 2.8 mA, max 3.0 mA
Would it be possible to just have suitable capacitors taking care of peak current and work with a coin battery? Low power mode allows taking one CO2 measurement per 30 second period which should be fine for a device such as ruuvitag. Of course, with a single coin cell battery power source one would still need some kind of DC-DC converter to increase the minimum voltage.
Maybe some future ruuvitag model could use stack of two coin cell batteries to enable sensors like this without DC-DC converter?
However, the data sheet for that sensor also says this (emphasis mine):
VDD and VDDH are used to supply the sensor and must always be kept at the same voltage, i.e. should both be connected to the same power supply. The combined maximum current drawn on VDD and VDDH is indicated in Table 4. Care should be taken to choose a low noise power supply (preferably a low-dropout regulator, LDO, with output ripple of less than 30 mV p-p), which is adequately dimensioned for the relatively large peak currents. Power supply configurations with large transient voltage drops are to be avoided to ensure proper sensor operation.
Powering the peak currents with coin cells is not very practical. Theoretically we could add some supercapacitor to provide the for peak currents, but then we’d need to add circuitry to trickle-charge the supercapacitor and the leakage current of supercapacitor would probably shorten the battery life significantly.
The sensor would be best paired with USB power supply, possibly with a rechargeable battery so the sensor could be disconnected from USB time to time as needed.