How can I slow down the current draw from a battery?

I have a sensor connected to a microcontroller which is powered by some batteries. It is currently drawing about a few milliAmps from the circuit. Is there a way to slow down the current draw?

Disconnect the sensor from power. Folks have success using an IO pin to power low current parts.
I wouldn't go more than 20mA, and not count on more than (Vcc - 0.8) doing that.

Perhaps better is to either disconnect the ground pin with a N-channel MOSFET or the power pin with a P-channel MOSFET. Logic level parts, lowest Rds you can afford because voltage drop across the MOSFET will be current * resistance.

Wow, lot few P-channel parts than N-channel available, and pricier too.

Well, the sensor needs to be always on.

What sensor is it?

Not feasilble to give the sensor its own power supply?

Motion sensor. Would adding a high value resistor to that powers the sensor do anything that could slow it down?

bradley:
Motion sensor. Would adding a high value resistor to that powers the sensor do anything that could slow it down?

No you will only stop it working. Read the data sheet, what does it say the current is?
You are stuck with that if you can't turn it off, or reduce the supply voltage to it. It will say if it can work at a lower voltage and thus current in the data sheet.
However you might then have to do a level shift on the interfacing lines.

Question:

dc42:
What sensor is it?

Answer:

bradley:
Motion sensor.

I think dc was meaning you to be a bit more specific, as to make and model... My experience on this forum is that we get the best assistance when when we give the most info....

Grumpy_Mike:
It will say if it can work at a lower voltage and thus current in the data sheet.

What does the data sheet say? Some are not easy to understand, so post a link to it if it's not helping you.

So current drawn by an object is dependunt upon the voltage applied and the 'resistance' of the object.

Generaly, the lower the voltage the lower the current drawn. ( Ohms Law )

So if a sencor is drawing too much current you only have three options.
a) use a different sencor,
b) run the sencor at the lowest voltage possible
c) turn the sencor off / on

As for C. If the sencor is a motion sencor, and it can take a reading in say 1 ms, and you can cope with not knowing the motion for 100 milli seconds, ( 10 times per second ) then you could save power by turning the sencor off for 99 ms, and on for 1 ms.

You might not says 99 % of the power due to start up current of the sencor, but you will save quite a bit. And 99ms is not long to wait for a reading. If you only need to know motion every 1/2 second, then yo can save even more.