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Topic: Is this right? Counter IC triggered by spinning magnet/hall effect sensor.  (Read 120 times) previous topic - next topic

Johnny010

Hey.

I am planning on making an wind speed measurement device as part of the STEM club at the school I teach at.

I was thinking a magnet could be used to trigger a hall effect sensor...making this relatively low power (no LEDs).

I have quickly scanned this paper Wind Speed Measurement Paper, they have used a similar idea except used an "always awake" MCU to count pulses from an LED being cut off by a vane from an LDR. I want to keep the IC (an ESP8266) asleep for an hour, wake up, get the number of rotations from a binary counter IC.

Essentially I was thinking this:

Vane turns -> Magnet Passes Hall Effect Sensor -> Hall effect sensor increments 16 bit counter -> MCU wakes up -> MCU triggers some parallel to Serial converter ICs to read and send the data serially to the MCU.

Now, the hall effect sensor may "jitter" around the voltage point where a counter IC may register multiple "pulses" on each pass of the magnet. So I was thinking, would a schmitt trigger and a capacitor of some sort be a way to "de-bounce" the signal?

The Schmitt would say only "trigger" once 2.5V out of 5 had been reached and the capacitor "absorbs" any noise/ bounces.

Is this the correct way to do this?

Does the counter Dual 16 Bit SN74lv8154 Counter already have some form of "de-noising"?

Grumpy_Mike

Quote
Now, the hall effect sensor may "jitter" around the voltage point where a counter IC may register multiple "pulses" on each pass of the magnet.
No it won't, hall switches will have hysteresis already.


Quote
Does the counter Dual 16 Bit SN74lv8154 Counter already have some form of "de-noising"?
No.

Sleeping for so long you will miss gusts and it will average out.


 

tinman13kup

How big of a unit are you talking? I'm thinking the reason optical sensors are used is because holes have no weight, unlike a magnet.

Like Mike said, this seems more like a mass airflow sensor rather than a wind speed sensor.
It's not a hobby if you're not having fun doing it. Step back and breathe

Johnny010

How big of a unit are you talking? I'm thinking the reason optical sensors are used is because holes have no weight, unlike a magnet.

Like Mike said, this seems more like a mass airflow sensor rather than a wind speed sensor.
A few grams of neodymium magnet at the end of a steel/wooden shaft shouldnt effect the moment of the shaft that much.

MarkT

The SN74LV8154 is a dual 16 bit counter with 8 bit parallel output which can be married with a parallel->serial shift register such as a 74HC299.

The SN74LV8154 can be configured as a single 32 bit counter if you want - each of the 4 bytes can be
accessed on the output bus using a separate select pin.  I've used it in the past as a frequency counter (since it can go to 40MHz or so), but its CMOS so very low power at low frequencies.  Its also available as through-hole and runs from 2V to 5.5V.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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