I fairly new in this arduino hobby. I am developing an automatic pets feeder that will run on batteries. I've done researches on minimizing power consumption.
I've successfully done the coding to sleep the board and to detach a mini servo when sleeping. Now, it is time for me to actually read the power consumption draw of the board to really see how low the current can go.
For this I am using a multimeter to read the amp while the board is running. However I am not sure about the connection to place the multimeter.
Measuring the current when powered by USB is not simple unless you can make up some connectors to allow a multimeter to be put into the power line.
It would be very straightforward to put a multimeter between a battery and the power jack very similar to the diagram you posted.
When you run power through the power jack there will be more energy wasted in the step-down to 5v.
I sometimes power my Uno from a pack of 3xAA Alkaline cells (4.5v) connected to the 5v pin. That would be very similar to the arrangement in your diagram.
I think I will give a try using the similar configuration with 4 AA batteries via the barrel jack. Yes, the power regulator via the jack is not energy efficient, but this is for temporary only. I will migrate my project to pro mini later, when I got all the concepts proven to my eyes.
I will also give a try on 3 AA battery into the Vin with maximum attention to the polarity. I never played with 5v and Vin pins as power input before. But I know they are so sensitive.
The power consumptions of an Uno and Pro Mini are very different, because the Uno includes 2 controllers and more. For lowest consumption use the Mini at 2.8-3.3V, i.e. from 2 batteries. Make sure that the Mini supports 3.3V operation, better both 5V and 3.3V for comparison. But check the voltage drop on the DMM before measuring current at low supply voltage.
Because the current is not constant when sleep modes are used, add a big cap (100-1000µF) to the multimeter, and/or to the board's inputs. Or use a scope instead of the DMM.
faztech:
I will also give a try on 3 AA battery into the Vin with maximum attention to the polarity. I never played with 5v and Vin pins as power input before. But I know they are so sensitive.
Vin is essentially the same as the barrel jack (but with a little less protection, IIRC) and I do NOT connect my 3 x AA cells to Vin. I connect them to the 5v pin. The fact that the voltage is a little below 5v does not matter. But you must never connect anything higher than 5v to the 5v pin.
Robin2:
Vin is essentially the same as the barrel jack (but with a little less protection, IIRC) and I do NOT connect my 3 x AA cells to Vin. I connect them to the 5v pin. The fact that the voltage is a little below 5v does not matter. But you must never connect anything higher than 5v to the 5v pin.
...R
Sorry my bad. I really meant 5v pin as per your advise.
I try to relate this diagram:
with this:
the difference is the former one connects the DMM's "Amp in" to GND/- of the power supply, and GND on ardunio to DMM's COM "port"
while the latter, connects the power supply's + to DMM's "Amp in" and DMM's com to the circuit input.
Hmmm... things get a bit more complicated (for me) to implement it, because I have one 9G servo in place which currently is taking power source from the 5v pin.
If I were to supply 3x AA cells into the 5v pin, meaning the servo is no longer able to directly draw power from the 5v pin.
So I did a bit of experiment using circuits.io and it works. But I am not sure if this can work on real circuit.
What voltage range can your servo accept? I have seen 9g servos with minimum voltage of anything from 3.5V to 4.2V. The servo may turn out to be the component that determines your battery life.
With just one servo to control, you could look at using an attiny85 for the final circuit. I have one running in a project of mine that is running in a low power but not a sleep mode (it needs to monitor several inputs) that consumes only 0.5mA. This is at 1MHz. Others more expert than me have made the tiny run at significantly less current than that, down to a few uA.
In terms of batteries, if you are using NiMH cells, you can use 4 cells connected to the 5V pin. When fully charged, that will be a little over 5V, for a little time, but I have never known this to cause a problem with the Nanos I use.
PaulRB:
What voltage range can your servo accept? I have seen 9g servos with minimum voltage of anything from 3.5V to 4.2V. The servo may turn out to be the component that determines your battery life.
I'm using Tower Pro SG90 9g micro servo. Based on some reference, the operating voltage range is 3.0 - 7.2 v and some reference ~4.8 v. This servo will be running only 4 times a day at most, and when running, it will run no more than 5 secs. The rest of the time it will stay idle, or I will program to detach the servo to further save more power. So it is not going to drain the battery power that fast. That is why I am metering the whole amp draw to calculate how long this project will last on AA alkaline cells.
Could be the servo still determines your battery life. The other components continue to run even when the servo is detached, draining the battery, but at a slow rate. They may continue to run OK even when the battery is down to 2.8V, but when the servo is next needed, there is insufficient voltage for it to run. What I am saying is that the component that needs the highest minimum voltage that can also determine the battery life, even if that component has not consumed very much of the energy from the battery. Does that make sense?
Let me clarify. The battery life is determined by two things. The rate at which current is consumed, and the lowest voltage at which the circuit can perform it's function. By minimising the current consumption, you can extend the battery life. But the component with the highest minimum voltage determines when the battery is effectively "drained".
