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Hall Sensor A3144, additional information:

 From a previous Blog Post on the A3144 Hall Sensor, the Hall Sensor device cannot directly switch a large electrical load as its output drive capabilities is limited to 25 mA. 

For large current loads an open-collector (current sinking) NPN or PNP Transistor is added to the output.

Test PCB built to understand correct operation of the A3144 Hall Senor.

When activated, Negative output to a LED, shunt jumper to transfer the output to further building blocks, for testing with devices requiring a Negative input.

Enhanced test PCB. 
Top left, 2N3906 PNP transistor, inverts the  Hall Sensor output, and reinforces - amplifies the output, the  A3144 Hall Sensor is limited to 25 mA, the transistor provides power for higher load devices.

Shunt jumper transfers the NEG output to the middle of the three screw terminals, device then needs a connection to the top screw terminal to the board +5V supply voltage. 

If a NPN transistor was placed here for the Hall Sensor output, refer to end of  this Blog Post, Hall Sensor toggle On - Off with a CD4013B 'D' type Flip - Flop. 

Hall Sensor output inverted and provides a POS input to the CD4013B.

Bottom right, 2N2222 NPN performs the similar function as above, reinforced and inverted POS output.

Shunt jumper transfers the POS output to the middle of the three screw terminals, device then needs a connection to the bottom screw terminal to the board  GND supply voltage. 

Hall Sensor, in the majority of cases, the preferable action is for the Hall Sensor output to be OFF until activated with a magnet.

Hall Sensor activated, NEG supply to LED.

Hall Sensor activated, POS supply to LED.

Building Blocks:

SN74HC04N, Hex Inverter, for converting the Hall Sensor NEG output to a POS output for connecting to other building blocks. 

Top Board, Test PCB, shunt jumper in place for NEG output.
Second from top, SN74HC04N Hex Inverter, NEG input from the Hall Sensor NEG output, converts to a POS output.
Third from top, POS output from the  SN74HC04N to the POS input of the CD4013BE  'D' Type Flip-Flop configured as a Toggle On/Off.
Bottom Board, reinforced/amplified output, LED to prove circuit.

First pass with a magnet over the Hall Sensor, the CD4013BE output will 'latch ON', LED will stay in this state indefinitely,  UNTIL, a second pass of a magnet over the Hall Sensor which will now turn the 'latch OFF', LED now OFF.

Multiple Hall Sensor can be connected in parallel, using two for example in different locations, one to turn the circuit ON, another one to turn the circuit OFF.

Normal non latched DPDT Relay, working as a latched DPDT Relay.

Numerous ideas, circuits and off the shelf modules can be found in other Blog postings.

The 'building blocks' are tried and tested, and their origins were thought through for multiple types of input, Servo, Reed Switches, Hall Sensors etc.........., and POS or NEG outputs.

By using a variety of 'building blocks', the only limitation is one's lack ingenuity!

Hall Sensor toggle On - Off with a CD4013B 'D' type Flip - Flop.

3D printed housings, purely functional, testing to find optimum for reliable operation.

For outdoor use, covering in Spray on Liquid Electrical Tape over the PCB and components, 3D printed parts to be sprayed will Filler Primer then a top coat black paint.