Re: Hall Effect Sensors

On Apr 8, 9:36 am, "Michael"
<QmQiQcQhQaQeQlQhQiQm...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Hi,

I'd like to interface Hall Effect sensor to a uC and have picked out the
A1301EUA-T (data***:http://www.allegromicro.com/en/Products/Part_Numbers/1301/1301.pdf) with no
particular reason - just seems easy to get hold off.

Now based on the graph at the bottom left on page 5, am I right in thinking:

Output from HES fed through a non-inverting amp. with gain of 250 would
produce a voltage of 625mV at 1G when the supply voltage is 5.0V? It just
seems a bit too easy (I'm guessing changes in temperature etc are going to
have a significant effect but right now just trying to get hold of the
basics.)

If I told you the application was going to be a motor tachometer - is it
'better' to feed the (amplified) voltage through a comparator and so convert
the analog signal into digital signal (when above a theshold go high, below
or at theshold go low type setup) or feed it into a ADC pin and work out the
digital signal using software? I'm worried that if I tied that to a ADC pin
then it could go over the pin's max voltage (5V) so would I need something
along the lines of a zener diode to dump any 'extra' voltage over say 4.5V
to be on the safe side?

I've only just started learning electronics so don't know if the circuit's
above are 'suitable' and so would appreciate any help. ( It's not a homework
assignment :-) )

Apologies if that's a few too many questions.

Thanks in advance,

Michael

Hi, Michael. In fact, it's not so simple, and unfortunately, I think
you've taken a wrong turn here.

The nominal output of the sensor you're looking at is around 1/2 Vcc
(around 2.5V for a 5V supply). Now apart from any drift caused by
variations in supply voltage, you'll have to apply the sensor output
voltage to an op amp to subtract out the 1/2Vcc.

The data *** says this quiescent output voltage is stable over time
and temp, but considering you're talking about such a small sensing
voltage to begin with, you are heading for problems here.

The good news is that there are hall effect sensors with digital
outputs that react to the presence of a magnet quite nicely, and will
have fast enough reaction times for a tachometer. You can forget the
analog stuff, hang a pullup resistor at the output of the sensor, and
just count the digital pulses. This is how it's done.

If you'd like further information or need help in sensor selection,
please post back with more info.

Cheers
Chris



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