i have an arduino with hc-12 , mq-5 gas sensor and dht11 and i am powering the arduino with a 9v battery through the power jack. and it runs for 15 minute and i noticed the buit in led of the arduino start to fade so i decided to measure battery voltage and i found it 7.8 volt.
how to explain that and how to solve that?
That one apparently draws something like 200mA when transmitting. Are you transmitting all the time with your device? That might drain a battery quite quickly.
That shouldn't make the onboard led fade since there would still be ample headroom for the onboard regulator to work with.
Are you using the onboard regulator to power all the modules you mentioned? Might not be a good idea; a separate DC-DC converter is a better solution.
Maybe it's also a good idea to revisit your choice to use a 9V battery for powering this project if it needs to be transmitting a lot of the time.
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No surprise if the 9V battery is a PP3 type intended to provide low current to devices such as smoke alarms
Use a 9V supply with a higher current capacity such as 6 AA cells in series
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Yep. See e.g. here: Battery Capacity
Typical drain (conservative estimate) 15mA. Trying to power a 200mA transmitter with it will give disappointing results.
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yes , i am transmitting each 2 second and i am using the onboard regulator.
now i am powering arduino from usb with a phone charger (5v dc 700ma) is it a good or at least sufficient? did it pose any threat for the circuit?
It's not ideal, but if it works, it's OK.
In general, don't try to power external modules apart from the Arduino itself through its onboard regulator. It's not designed to handle a lot of current. Usually when powering from USB it's not so much of a problem since the regulator is bypassed in that case and the only limitation you have is whatever the USB port can supply.
A 700mA supply will work OK, but it's a bit on the weak side. 2A USB chargers/supplies are common these days and would be a better idea. However, again, if it works the way it is now, then live with that.
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USB power does not go through the regulator so is perfectly OK.
That should be OK. I might have missed which Arduino you're using; e.g. an Uno has a resetable fuse rated at 500 mA; if you exceed that, it will disconnect the power.
Exactly, I included that in m post you quoted.
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