Hall switch not producing low output

ZOR

Senior Member
I have been through 4 devices type A3213eua-t hall switches. Aail to go down to ov output, typically 0.04 volts. The datasheets show a 50k resistor going from 5v supply pin to the output pin. I used to get away with 10k resistors, however to get as near to 0 volts I had to use 100k resistors. Has anyone else had these issues. Thanks
 

rq3

Senior Member
I have been through 4 devices type A3213eua-t hall switches. Aail to go down to ov output, typically 0.04 volts. The datasheets show a 50k resistor going from 5v supply pin to the output pin. I used to get away with 10k resistors, however to get as near to 0 volts I had to use 100k resistors. Has anyone else had these issues. Thanks
The datasheet shows the output as an open drain N-channel mosfet with an absolute maximum current rating of only 1 milliamp! It also says that at a drain current of 1 mA, the output voltage may be as much as 0.300 volt. They appear to imply that the output is strictly ON-OFF for logic purposes, so I'm not sure why you need the output to get so very close to zero?

The higher the output resistor, the lower the voltage will go, within the limits of the logic gate or other device the output is attempting to drive.
 

erco

Senior Member
For a Picaxe, anything below 1.2V is low. Who cares about a scrappy little 0.04V?

 

ZOR

Senior Member
Thanks rq3. I have used this switch with no problems, going from almost 5v to 0 volts. I was beginning to wonder if this device was a sensor and not a switch. I might have to rewire the device to an analog pin and use it's voltage. Just seen erco's reply, thanks. Will try another device when received (on order) and see what happens.

EDIT:
I forgot to say, I have read that the device is normally off until a magnet is next to it. Mine is high all the time until going low with magnet. ??
 
Last edited:

hippy

Technical Support
Staff member
I forgot to say, I have read that the device is normally off until a magnet is next to it. Mine is high all the time until going low with magnet. ??
That would seem to be correct; "off" is the MOSFET not activated, which with a pull-up will present a logic high to the input pin, when "on" the MOSFET is active, will pull the input pin signal down to low.
 

rq3

Senior Member
Thanks rq3. I have used this switch with no problems, going from almost 5v to 0 volts. I was beginning to wonder if this device was a sensor and not a switch. I might have to rewire the device to an analog pin and use it's voltage. Just seen erco's reply, thanks. Will try another device when received (on order) and see what happens.

EDIT:
I forgot to say, I have read that the device is normally off until a magnet is next to it. Mine is high all the time until going low with magnet. ??
Yes, it is normally off, meaning that the output mosfet is in a non-conducting state, so that the mosfet drain (the "output" pin) is pulled up to the supply voltage by the resistor you choose. When the device is ON (a magnet near it), the mosfet conducts, and "shorts" the output pin to ground to the best of its ability. The higher the resistance you choose, the closer to ground it will get, because the mosfet doesn't have to shunt as much current to ground.

Open drain and open collector outputs are very common. You just need to reverse the logic in your own head. You are probably used to thinking that "off" is "low", and "on" is "high". This is just the reverse, that's all.

To interface the output to a Picaxe, you would use, say, a 100Kohm resistor between the output pin and the +5 volt supply. The output pin would then go to any Picaxe digital input (NOT an ADC input).
Your Picaxe code would then ask that pin what it was seeing. If there is no magnet, the Picaxe would see a "high". If there is a magnet, the Picaxe would see a "low". The output voltage does not vary with the magnetic field strength, it only switches from off (high) to on (low) when a sufficiently strong magnet is near.

If that's not what you are after, there ARE hall effect sensors that DO output a variable voltage with varying magnetic field intensity.
 
Last edited:

ZOR

Senior Member
Thanks hippy and rq3, now I understand how it's on/off state is. I have alternative devices to these coming soon so I can compare them to these ones. Maybe I should have gone for sensor types as they are to be used for setting rotational limits on geared stepper motors. Using the switch versions makes it tricky mounting the devices in exactly the positions required to stop the rotational position whereas I could have used the voltage level in addition to position to fine tune limits. Thanks again
 

Goeytex

Senior Member
I have used Honeywell SS413 (bipolar) and SS441 Hall sensors with excellent results. These will easily pull down a 10K resistor as they can sink up to 20 ma. I used the SS441 as a crankshaft/flywheel sensor for a Picaxe based ignition system on a two cylinder mower engine. Nice clean pulses.

Correction:
The ignition uses a Honeywell SS441R
 
Last edited:
Top