I am making a simple burglar alarm that uses a PIR sensor to detect an intruder and sound an alarm buzzer. I would like to make this use as little power as possible so that it can last a long time on batteries.
The Arduino must supply constant current to the PIR sensor. However, it only needs to read from the PIR sensor, via a digital pin, once per second.
Apparently the sleep states available on the AT chip are:
Will all of these allow the chip to continue supplying current via its output pins?
Is there significant overhead to entering and exiting sleep states?
Is it hard on the chip to go in and out of sleep states?
I've also read that the voltage regulator has high overhead and consumes a good bit of power even when the processor is sleeping.
Would it be dangerous to bypass the voltage regulator with unregulated current from AA batteries? And would the board function correctly with 4.8V? Does anyone know of a lower overhead external voltage regulator that I could buy?
Think you will find the PIR will draw whatever it needs to run it's internal circuitry and there would be no difference when it gives an output.
Don't believe that the PIR would need any constant current as you suggested.
Battery supply is esentially a voltage regulated supply in that they output a steady voltage over the range of their life(dry cell) and nicad or NiMh are similar with their output voltage fairly constant over the discharge time.
Usually what is referred to as an unregulated supply would be a transformer with rectifiers and smoothing capacitors or some switchmode supplies.
Not sure about the Arduino regulator supplying your PIR, I wouldn't do it that way.
Depends on the Arduino type as to what voltage it will run on, some will work on 3.3v as far as I know.
Hi, I would be investigating how much power it takes to power up the PIR each time, most of these can now come with their own battery.
Powering up a device usually takes more energy than the device consumes when it is running, powering up every second may not be power saving.
The arduino running in its minimum physical setup and sleep would possibly be an advantage.
As bluejets has said you need to get your understanding of voltage and current correct.
Do you know OHMS LAW?
Do you have a meter to help your measure your project?
bluejets:
Think you will find the PIR will draw whatever it needs to run it's internal circuitry and there would be no difference when it gives an output.
Don't believe that the PIR would need any constant current as you suggested.
Battery supply is esentially a voltage regulated supply in that they output a steady voltage over the range of their life(dry cell) and nicad or NiMh are similar with their output voltage fairly constant over the discharge time.
Usually what is referred to as an unregulated supply would be a transformer with rectifiers and smoothing capacitors or some switchmode supplies.
Not sure about the Arduino regulator supplying your PIR, I wouldn't do it that way.
Depends on the Arduino type as to what voltage it will run on, some will work on 3.3v as far as I know.
Thanks for the reply I guess by constant current what I meant is, constantly available to supply current as needed and constant voltage. Do you know if sleeping leaves it in such a state? Or are outputs disabled? I think I will just try it and find out, that is simple enough to check.
TomGeorge:
Hi, I would be investigating how much power it takes to power up the PIR each time, most of these can now come with their own battery.
Powering up a device usually takes more energy than the device consumes when it is running, powering up every second may not be power saving.
The arduino running in its minimum physical setup and sleep would possibly be an advantage.
As bluejets has said you need to get your understanding of voltage and current correct.
Do you know OHMS LAW?
Do you have a meter to help your measure your project?
Thanks. I am not so concerned about specifically how much power start-up requires but about power usage more holistically. I think I will run some trials and see how long it takes to drain batteries in certain configurations. Also I believe I can use the PIR sensor output as an interrupt so the Arduino only has to wake up when the sensor picks something up.
As bluejets has said you need to get your understanding of voltage and current correct.
Do you know OHMS LAW?
Do you have a meter to help your measure your project?
What do you mean exactly? Yes & yes but I think I will do some trials rather than trying to extrapolate from what the dmm says.
The state of the output pins is not affected by sleeping, so you can supply power to the PID through a sleep.
There is overhead associated with sleeping, but compared to other stuff you're likely doing it is minimal.
I have never read anything that hints about shortening device lifespan by repeatedly sleeping/waking up. I don't think it's hard on the microcontroller to do that.
There are low quiescent voltage regulators. Many LDO regulators report less than 100 uAmps quiescent current these days.
If you're thinking of doing a bare bones version, you can skip the regulator altogether and just power it with the batteries straight. As long as you don't need precision timing, the difference between full battery and almost empty battery isn't that big a deal. See Nick Gammon's Low Power page for excellent information.
TanHadron:
The state of the output pins is not affected by sleeping, so you can supply power to the PID through a sleep.
There is overhead associated with sleeping, but compared to other stuff you're likely doing it is minimal.
I have never read anything that hints about shortening device lifespan by repeatedly sleeping/waking up. I don't think it's hard on the microcontroller to do that.
There are low quiescent voltage regulators. Many LDO regulators report less than 100 uAmps quiescent current these days.
If you're thinking of doing a bare bones version, you can skip the regulator altogether and just power it with the batteries straight. As long as you don't need precision timing, the difference between full battery and almost empty battery isn't that big a deal. See Nick Gammon's Low Power page for excellent information.
