I’ve been working on a school project which is a wireless carbon monoxide detector that activates a servo motor on the other wireless circuit. I will attach the circuit diagram I came up with below.
For the CO sensor circuit, I will be using a CO sensor that draws 32 mA, a wireless transceiver that draws around 12 mA (nRF24L01 transceiver), and an arduino nano that draws 5 mA (?). That would be 49 mA in total. If I were to use 4 AA batteries that are rated for 2800 mAh, would that mean I would be able to run the circuit for 228 hours before the battery dies? (11200 mAh / 49 mA = 288.57 hours).
I haven’t created the second circuit yet but it will use the same wireless transceiver (12 mA) and a 9g servo motor (5 mA - 700 mA). This will also hopefully be powered by 4 AA batteries but the servo will only need to turn once when the sensor detects a certain level of carbon monoxide. So if the servo never needs to activate, would that mean this circuit would run for 509 hours? (11200 / 22 = 509). These seem like very high values but the circuit doesn’t seem to draw too much power. Is that all the information I need or am I missing something?
Any suggestions for the circuit diagram would also help!
Your calculations are wrong;
Your batteries will be in series, the same current flows through all of them so you don't add the capacities, the capacity is as per 1 battery, so 2800mAh.
Are the currents you quoted measured or from the data sheet? Measure the actual current.
I don't know how accurate specified battery capacities are, but you can expect that what manufacturers quote are in Ideal conditions, real life capacity will probably be lower.
You also need to know at what voltage your devices stop working; the batter voltage will drop slightly as it discharges, you need to see if this will be a problem.
So does having 4 batteries increase the voltage? Would that be a problem for the arduino?
2800 mAh would be enough anyways because the circuit only needs to run for a few hours. I'm hoping we return to school soon so I could actually measure the current and these calculations are just based off of datasheets and assumptions.
4 in series increases the voltage, 4 in parallel increases the current capability.
If you have to ask this then please get hold of a multimeter and some batteries and connect them together in different ways and see what effect it has on the voltage.
You could look at whether you can switch the radio and sensor off to save power .
For example turn the CO sensor and transmitter on did say for only 5 seconds in every minute - you’ve then reduced consumption by a factor of twelve . You’ll need to look at whether this is workable for the transmitter /sensor , but an option to look at .
hammy:
You could look at whether you can switch the radio and sensor off to save power .
Just a caution here ... this is a great idea but powering down the nRF24L01 radio may not be as straightforward as it should be. Actually, powering it down is easy, but waking it back up is not. See this thread and other links within:
Ah I would only be getting 1.5 volts if the battery was wired up in parallel.
The sensor I'm using is a MiCS5524 compact MOS sensor. The sensor datasheet does not list a preheat time, the only downside is that it measures multiple gas types including propane and iso-butane.
