HiLetgo 2pcs NJK-5002C Hall Effect Sensor Proximity Switch NPN 3-Wires Normally Open

It requires a magnetic field to change state. If a magnetic field is not involved -- NO WORKY PEOPLE! Magnets work well!

I'm currently using one of these to sense the state of my overhead garage door. It is behaving and functioning as a Hall Effect Proximity Sensor should. Each one comes with a small magnet for activation. I found a location where I could mount the sensor on a bracket the holds the garage door tracks. I just needed to enlarge a hole a bit to hold the sensor. I epoxied a magnet to the edge of the garage door where it would be aligned with the sensor when the door is closed. I have about 3/8" (about 9 - 10 mm) air gap between the magnet and sensor, and it is working fine.I have the sensor connected directly to the Raspberry Pi as follows:The sensor's brown wire connects to pin 2 of the GPIO header for the +5V supply.The sensor's blue wire connects to pin 6 of the GPIO header for the ground connection.The sensor's black wire connects to pin 8 (or any input of your choice -- configure your software to match.)The black wire/Pin 8 also needs to connect to a resistor (2200 - 4700 ohm is fine) and the other side of that resistor connects to pin 1 (3.3 V) of the Raspberry Pi GPIO connector. The black wire in the sensor provides an open-drain output, which means that it can provide a ground-level signal to pin 8 in one state, but to provide a voltage to pin 8 in the other state, you need to use the resistor (pull-up resistor) that connects to the Pi's 3.3V The Raspberry Pi inputs cannot tolerate more than 3.3 volts on an input pin.The specifications state that it has an NPN transistor output, and that configuration would be called open-collector, which in this application, works the same as the open drain output on what is clearly a FET: The on-state (conducting) voltage drop from black to blue wire was measured at about 20 millivolts.

I like these sensors because they are sealed hall effect sensors. The cylindrical shape makes them easy to mount with just a drill. They respond to the south pole of a magnet.However, if you need to interface them to 3V logic, you need to level shift, current limit, or use a blocking diode.

No where in the product description does it state that it requires a magnet to work. It will not work with just ferrous metal, like I need it to. It does come with a magnet, but that won't help for my application.

Works great. Heavy duty stainless steel body. Comes with a magnet and has a LED light indicator that turns on when the sensor detects the magnet. Wires are little thin but should withstand medium duty use.

Advertised as a Hall effect. It is not.Will not work without a magnet.(A.K.A reed switch)Works perfect as a reed switch.2 stars because of bogus description.

These hall sensors perform as well as sensors costing much more.

This is a hall effect sensor, just not the kind some of the other commenters were looking for. A reed switch is not going to operate at the ~4kpps that I'm using mine for. This one requires an external flux source (magnet) rather than containing one internally that any ferrous object will interrupt. Thus the reason that it can detect at up to 10 mm, the other kind generally must be much closer, like ~2 mm.