electromagnetismhall-effectmagneticssensor
Would there be any possibility to convert a three-wire hallsensor to a 2-wire equivalent.
The connections are a V+, GDD and OUT.
The voltage between V+ & GDD would be 24V and the OUT port would reflect the influence of a magnetic field on the sensor.
I assume that if one would connect the wires in the correct way you could get an sum or subtraction hence enabling a 2-wire circuit.
Thank
The measured current has to flow through the package to produce any result.
Therefore, you have to cut the wire, and solder one end to one of the terminals, and the other end to the other terminal.
The nominal output is 1/2 Vcc, assuming you are using the birirectional variant. The datasheet states:
Datasheet, page 15
Quiescent output voltage (VIOUT(Q)). The output of the device when the primary current is zero. For bidirectional devices, it nominally remains at VCC ⁄ 2. Thus, VCC = 5 V translates into VIOUT(QBI) = 2.5 V. For unidirectional devices, it nomi- nally remains at 0.1 × VCC. Thus, VCC = 5 V translates into VIOUT(QUNI) = 0.5 V. Variation in VIOUT(Q) can be attributed to the resolution of the Allegro linear IC quiescent voltage trim, magnetic hysteresis, and thermal drift.
QUNI means Quiescent (e.g. no current flow), unidirectional variant. QBI means Quiescent, Bi-Directional variant. VIOUT is the name of the output pin. See the pinout on page 1.
Since you say you are getting ~1.6V, I would guess you're using the bidirectional variant, and powering it from 3.3V.
I don't know how you're having trouble figuring out the current, it's very simple:
Datasheet, page 15
Sensitivity (Sens). The change in device output in response to a 1 A change through the primary conductor. The sensitivity is the product of the magnetic circuit sensitivity (G / A) and the linear IC amplifier gain (mV/G). The linear IC amplifier gain is pro- grammed at the factory to optimize the sensitivity (mV/A) for the half-scale current of the device.
There are multiple versions, with different sensitivity.
From page 2 of the datasheet:
The sensitivity is given in mV/A. Therefore, with a device with a 40mV/A sensitivity, 1A of current through the device will result in the output voltage increasing by 40mV.
The overall equation is:
$$V_{IOUT} = ( Vcc * OffsetScaling ) + ( Scaling Factor In Volts * Amps ) $$
\$OffsetScaling\$:
\$Scaling Factor In Volts\$:
Therefore, for the bi-directional variant, with 40mv/A sensitivity, the output voltage will be: $$V_{IOUT} = Vcc*0.5+ 0.040 * A$$ The uni-directional variant with 40mv/A sensitivity would be: $$V_{IOUT} = Vcc* 0.1 + 0.040 * A$$
0.040 is 40mV in Volts. Change to match your device sensitivity.
The HAL508 and Optek OH180U are both Hall Effect SWITCHES with hysteresis. The HAL has an open drain output ant the Optek has an open collector output, both on pin 3. When you look at the magnetic specs in the data sheets, after converting Gauss to milliTeslas, you'll see that the two sensors are very compatible.
Since switches are on/off, I assume that the function is to say whether the Hi Hat is open or closed, not to read out the linear position of the hi hat.
The circuit is rather confusing. Why you would tie an open drain high using the output of an op amp is simply beyond me. It's hard to believe that anyone would want to handle a switch in this fashion, even if you need to do inversion and/or level shifting. I suppose its possible that this funky circuit forms some sort of oscillator that when low pass filtered gives you a distance measurement, perhaps explaining the capacitor, but we'd really need to know what is being used as the output of this circuit to know.
Is it possible that the ORIGINAL original circuit used some sort of ratiometric Hall sensor, and not a switch?
Best Answer
A two wire sensor surely implies that the device becomes one that operates as a current device. The current would vary between two levels depending upon the magnetic field sensed by the Hall device. You have not indicated if the sensor is an on/off type detector of if it is an analogue device intended to show the relative strength of the magnetic field detected. In either case your target implementation could be designed to work as a 4-20mA type device. For the on/off type design the circuit could simply switch between 4mA and 20mA. The analogue implementation would vary continuously over the 4 to 20mA range. You can find various 4-20mA circuit designs on the web but the easiest is to deploy an IC chip that performs the 4-20mA driver function. Two possibilities to use for this are the Analog Devices AD5750 or the Texas Instruments XTR117.