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Mike_K
join:2014-03-27

Mike_K

Member

Hall sensor sleep time measure 100Hz battery solution

Hello All,
it is my first time here.
I've got a hall sensor which needs about 5mA, ring with some magnets and I need to have a possibility to count it, it is about 100Hz. I just need to count them and increment in my C programme in uC. According to Shannon's law I should generate minimum 200Hz wave. But I want to reduce current supply, according to this article »www.digikey.com/en-US/ar ··· switches Figure 7 I can switch on/off the voltage supply just to sleep the sensor. In my case 30us should be enough (start-up time and time to read a value), so I should generate 200Hz wave with 30us duty cycle, yes? If I generate 100% duty cycle everything for me is clear, but in my case according to this article would it work? I am afraid to lose samples. Can somebody explain it to me how it works with this sleep time? Any held needed.
Thanks a lot.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

Look at Figure 7 on that page: The typical sample time of 48 us for each 50 ms period reduces the average current draw to 8 uA or even 5 uA.

BTW If typical sample time is 48us, you can't have 30us duty cycle.

Please read the Rohm IC datasheet carefully. It will probably give you ideas for lowering average current using a capacitor which is charged at very low current but can provide the burst power for each sample.
Mike_K
join:2014-03-27

Mike_K

Member

Hey, thanks for answering.
My sensor is another one, this article is just an example. In my situation, there is about 30us just to make the measure. I've got frequency 100Hz, so period time should be minimum 200Hz. So period time=5ms and duty cycle=30us. These are facts. My question is, acording to the article example, if it works or not, as I know it should. Can You explain it to me? How it works that I will not lose any samples?
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

1 edit

lutful

Premium Member

said by Mike_K:

I've got frequency 100Hz

What exactly is the application? Fixed 100Hz frequency or maximum 100Hz frequency?

*** Found a good article for you which explains why in general you need higher than 2X frequency sampling. »www.wescottdesign.com/ar ··· ling.pdf

cowboyro
Premium Member
join:2000-10-11
CT

cowboyro to Mike_K

Premium Member

to Mike_K
From what I read you don't power it with pulses, it wakes up and goes to sleep by itself.

ROHM’s Hall effect ICs typically have a sampling period of 50 milliseconds. As shown in Figure 7, the device wakes up for a 48-µs sample of the magnetic field and then returns to sleep.

Therefore, if I am not misreading this then the best you can do is 10Hz.