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Author Topic: Stall warning how to????  (Read 256 times)

Aitch1969

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Stall warning how to????
« on: October 23, 2018, 10:22:11 AM »

Hi all
Any help or advice please

I am trying to make a stall warning device in reverse
I.e. Like an air speed switch that will switch a circuit at a given air speed.

Start point is to use an air pressure differential sensor and pitot tube.

I have found this sensor commonly available
MPX2010DP Differential Air Pressure Sensor
1.45PSI (10 kPa)  Dual Port.

So I will get a variable voltage output according to speed (pressure differential)

What I am looking for is to be able to use this as a switch at a given (variable) output voltage. So I can operate a separate circuit (close switch) at or above a specific air speed. (switching will be at between 20 and 100 Pa)

I am looking for something that will be accurate but use as small a parts count as possible to keep costs and complexity down.

I am sure there's something out there I can use but am. Sfuuering Google blindness trying to find it.

Thanks
Aitch
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Dillwhacker

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Re: Stall warning how to????
« Reply #1 on: October 23, 2018, 10:37:07 AM »

You can easily use an op-amp to make a comparator, like this...
http://forum.arduino.cc/index.php?topic=15001.0
Replace the two fixed resistors with a preset trimmer pot if you want to make the threshold adjustable.
You can put a mosfet on the output of the opamp to switch higher power loads if needed.
HTH
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Aitch1969

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Re: Stall warning how to????
« Reply #2 on: October 23, 2018, 10:46:44 AM »

You can easily use an op-amp to make a comparator, like this...
http://forum.arduino.cc/index.php?topic=15001.0
Replace the two fixed resistors with a preset trimmer pot if you want to make the threshold adjustable.
You can put a mosfet on the output of the opamp to switch higher power loads if needed.
HTH


That goes a little above my head
I am not an electrical engineer by trade acronyms and such mean little to me.

I know what I'm after is a comparator circuit. It's in the name.

Also know I'm looking to switch on very low voltage readings and probably needs to be very fine. I. E. 0v may be 0 kmph and 2v may be 100kmph so variance is little and adjustment needs to be fine

Aitch
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Dillwhacker

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Re: Stall warning how to????
« Reply #3 on: October 23, 2018, 10:59:31 AM »

Using a decent op amp and quality resistors will give you accuracy and repeatability to within a few millivolts.
You can get 15 turn preset potentiometers to allow fine adjustment, or you can add fixed resistors to each end of the pot to expand the range it covers.
I'm not sure you will find what you want off-the-shelf though. I may be wrong....
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Aitch1969

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Re: Stall warning how to????
« Reply #4 on: October 23, 2018, 03:54:51 PM »

Using a decent op amp and quality resistors will give you accuracy and repeatability to within a few millivolts.
You can get 15 turn preset potentiometers to allow fine adjustment, or you can add fixed resistors to each end of the pot to expand the range it covers.
I'm not sure you will find what you want off-the-shelf though. I may be wrong....

So an op amp is a chip like this
N0nA5qM2ZDBG19i2D4fuWTFDjUmCWb5ImwfF6jisEW_kAaAjAIEALw_wcB
??????

Or so Google tells me!?

And then some how or other I have to connect the pressure sensor and a load of resistors and a variable resistor then I can use the whole shebang as a switch.

I'm new to this (seriously) I have a bag of components now but still lack knowledge on how to connect them.

Aitch
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Tim Chambers

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Re: Stall warning how to????
« Reply #5 on: October 24, 2018, 12:08:56 AM »

why complicate things, just use the same system as full size a simple flap on the leading edge of the wing that flicks up near the stall to switch on the stall warning.https://goo.gl/images/PvRuDS
« Last Edit: October 24, 2018, 12:27:21 AM by Tim Chambers »
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Dillwhacker

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Re: Stall warning how to????
« Reply #6 on: October 24, 2018, 12:41:01 AM »

Agreed, but mechanically, it would be hard to implement, adjust & calibrate..
But you are so right - a stall is not airspeed, it is AOA, so yep, that's a better idea.

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Aitch1969

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Re: Stall warning how to????
« Reply #7 on: October 24, 2018, 10:06:46 AM »

I have called it a stall warning as I want to have an indication of a precise airspeed.

Some amount of research into op-amp and I find this is an operational amplifier used to amplify a signal voltage as a voltage range such as the pressure sensor of 0-25mv is very hard to read/calibrate. Then this amplified voltage may now be in range for example of 0-5 volts. And far easier to read/calibrate.

Then what is needed is a voltage comparator to work as a switch.

I have found this
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F192653102914

An LM393 comparator board.
But as with so many of these things origination from China there is very little detail on the specifications so I don't know if it or a version of it would be suitable for the low input voltage range that the pressure sensor would provide.

Although there are several UK resellers they seem to have little to no actual knowledge of the product and just copy and paste the original text from China.

Does anyone have experience of these or know of a proper spec sheet that would indicate the input voltages / sensitivity

Thanks
Aitch

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