hello, am new here, studied digital electronics 40 years ago, then became a programmer instead, am very rusty.

my application is a number of IOT sensors to be hand made using raspberry picoW boards.

bought a pack of A3144 hall effects without properly researching, these require 4.5v minimum, i should have ordered something 3.3 volt capable, however am wondering if i can still make these things work for me, with careful circuitry.

my application is various 24v and 12v boat engines, i need to monitor rpm and float position, etc, in various situations.

the 24v system will suffer peaks of up to 28v under charging conditions, and up to 16v in the 12v system.

the picoW boards will be powered from 3.3v buck converters tied to the battery rail, and will not have the 5v needed to power the hall effects.

can i just wire these transistors as open collector, and use a large enough pull up resistor, to the battery rail, as is commonly described for 12v systems?

can this work at 24v to 28v on the rail, or should i have more protection on the GPIO pins?

have seen advice on this forum to use one or more diodes in series to protect the GPIO, is this correct?

my hope is that, being open collector, the pullup power trick will not draw current when the transistor is quiescent - am i thinking correctly?

do i have any of this right, at all?

could anyone spare the time to help me work out a safe circuit for this?

i would not hold you responsible, i just do not want to have to blow up any boards, working out how to do this.

any advice very much appreciated, i hope i am explaining properly.

 

I'm not sure exactly what a "hall effect transistor" is. I will download the datasheet and have a look. A schematic or block diagram of the power connections available would be helpful. Can you do that for us?

 

hi,
This PDF will provide some additional background information for your database.
E

 

Wow. The part went out of production in 2005 and is no longer being made. I strongly suggest you dump those parts and look for an alternative. You may be making devices that cannot be serviced or maintained. The datasheet note says to consider the A1104 as a replacement. An EOL from almost 2 decades ago is not something I would ignore.





The datasheet shows CLEARLY that the device can be powered from any voltage in the range of [4.5v, . . ., 24V]. It has an internal voltage regulator to do what it needs to do. Since the output is open collector pulling it up to +3.3V will work just fine.

 

thank you everyone for your comments.

i presume this part was cheap online because it has been discontinued.

am sort of stuck with what i ordered, at the moment, and generally i would sooner return to reed switches, which i understand, and are passive, so will not draw power when idle, however i really would like to understand what i have bought, what i might be able to do with it, and now also - why it went out of production.

at the moment i do not understand most of the rest of the advice you have given, and i am studying carefully, will answer when i can.

in the meantime, attached is my reference circuit, where +5v is actually between 22 and 28 +ve, or between 10 and 16 +ve, and i would expect to need a much larger value for R1 and, i presume, other components to protect my GPIO pins?

 

thank you everyone for your comments.

i presume this part was cheap online because it has been discontinued.

am sort of stuck with what i ordered, at the moment, and generally i would sooner return to reed switches, which i understand, and are passive, so will not draw power when idle, however i really would like to understand what i have bought, what i might be able to do with it, and now also - why it went out of production.

at the moment i do not understand most of the rest of the advice you have given, and i am studying carefully, will answer when i can.

in the meantime, attached is my reference circuit, where +5v is actually between 22 and 28 +ve, or between 10 and 16 +ve, and i would expect to need a much larger value for R1 and, i presume, other components to protect my GPIO pins?

You have a serious flaw in your design concept. If you use that circuit, you will FRY whatever microprocessor you connect it to.
You want to connect R1 to whatever voltage is providing power to the microprocessor. I'm also not sure the capacitor is a good idea either. This is a switching circuit, not an analog circuit. The value of R1 should be made small enough to allow for it to provide a reasonable rise time when the transistor turns off, but not so small that it draws excessive current when the transistor is on. The capacitor will just make the rise time worse, and it provides no conceivable benefit.

 

yes, i know that will fry my board, that is why i made this post.

at the moment my project has only a 3.3 volt supply, from a bucking supply board on the battery rail.

have been rooting around looking for other hall effect transistors, and so far i cannot find anything that will accept less than 3.8 volts operating voltage.

the boards will accept up to 5v power, and i could replace my power boards to do this, in order to get a Vsys that i can run the halls on, however that means bucking the battery rail twice, to power the project, and this does not seem efficient, to me, since my project is parasitic, and must draw the least possible current from the battery.

will continue to hunt for hall effects that will work on 3.3v, however in the meantime am becoming more and more convinced that reed switches are the best answer, in this case.

thank you very much for all your advice.

 

yes, i know that will fry my board, that is why i made this post.

at the moment my project has only a 3.3 volt supply, from a bucking supply board on the battery rail.

have been rooting around looking for other hall effect transistors, and so far i cannot find anything that will accept less than 3.8 volts operating voltage.

the boards will accept up to 5v power, and i could replace my power boards to do this, in order to get a Vsys that i can run the halls on, however that means bucking the battery rail twice, to power the project, and this does not seem efficient, to me, since my project is parasitic, and must draw the least possible current from the battery.

will continue to hunt for hall effects that will work on 3.3v, however in the meantime am becoming more and more convinced that reed switches are the best answer, in this case.

thank you very much for all your advice.

I gave you the solution to your problem. Power the sensor from any convenient voltage allowed by the device datasheet in the range of 4.5 volts all the way up to 24V. IT HAS AN INTERNAL VOLTAGE REGULATOR FOR ITS OWN PURPOSES. Connect the output to your micrprocessor powered from 3.3V and connect the pullup resistor to the very same 3.3v power source. The value of the pullup resistor will be a compromise between a small value for a rapid risetime and a larger value to limit the current the transistor must sink when it is turned on.

 

Do it like this:

I hope this provides some clarity.

 

oh, yes, i think i get it now, the output transistor pulls low.

thank you very much, very much appreciated.

 

oh, yes, i think i get it now, the output transistor pulls low.

thank you very much, very much appreciated.

And when the transistor of OFF, resistor R1 pulls the GPIO.1 line high. This is a passive pullup and the rise time will depend on the total capacitance to ground.