A3144 Hall effect sensor: specs and pinout
The chip is the Allegro A3144, a unipolar Hall-effect switch (Allegro lists it as discontinued); the module chip on the listing board is not verified. The output turns on when a magnet of the right polarity gets close and releases when it moves away.
Specs
| Spec | Value | Source |
|---|---|---|
| Supply voltage VCC | 4.5 V to 24 V (abs. max 28 V) | source Features and Absolute Maximum Ratings (PDF p.2); Electrical Characteristics (p.3) |
| Output | Open collector, sinks up to 25 mA | source Features (PDF p.2) |
| Output saturation voltage | 175 mV typical, 400 mV max at IOUT 20 mA, B above BOP | source Electrical Characteristics (PDF p.3) |
| Output leakage current | 10 uA max at VOUT 24 V, B below BRP | source Electrical Characteristics (PDF p.3) |
| Operate point BOP (A3144) | 70 to 350 gauss at 25 C | source Magnetic Characteristics (PDF p.3) |
| Release point BRP (A3144) | 50 to 330 gauss at 25 C | source Magnetic Characteristics (PDF p.3) |
| Hysteresis (A3144) | 20 gauss minimum, 55 gauss typical | source Magnetic Characteristics (PDF p.3) |
| Supply current | 4.4 mA typical, 9.0 mA max, output off | source Electrical Characteristics (PDF p.3) |
| Operating temperature | -40 C to +85 C (E suffix); -40 C to +150 C (L suffix) | source Absolute Maximum Ratings (PDF p.2) |
Power
| Value | Source | |
|---|---|---|
| Supply | 4.5 V to 24 V (chip) | source Electrical Characteristics (PDF p.3) |
| Current | 4.4 mA typical, output off | source Electrical Characteristics (PDF p.3) |
Chip pins
These are the pins of the chip on the module, from the chip datasheet. The module's own header may label or expose them differently.
These are the 3 leads of the Allegro chip. The module board (any pull-up, comparator, indicator LED, header order) is not covered by an official document; check which rail your module pulls the output up to before connecting a 3.3 V input.
| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| 1 | SUPPLY (VCC) | 4.5 V to 24 V | Pinning shown viewed from branded side | source PDF p.2 |
| 2 | GROUND | 0 V | source PDF p.2 | |
| 3 | OUTPUT | open collector | Sinks up to 25 mA; needs pull-up | source PDF p.2 |
Build with it
Project ideas for the A3144 Hall effect sensor. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.
- Wheel speed counter: A 5 V board meets the chip's 4.5 V minimum supply and counts one pulse per magnet pass.
- Lid-open detector: The sensor module is undocumented, so power it from 5 V and send its output through the 2-channel level converter (5 V side to the module, 3.3 V side to the ESP32) instead of assuming a pull-up level. Learning project.
- Fan speed readout: One magnet gives one pulse per turn; keep the magnet small so the blade stays balanced.
- Magnet-triggered buzzer: The chip's output is open collector and pulls low when a magnet is near. The module is undocumented, so route its output through the level converter before the ESP32 input.
Common mistakes
- Do not run the bare chip from 3.3 V: the sheet says VCC operation starts at 4.5 V. Power it from 5 V and pull the open-collector output up to your logic level (source: link, PDF p.2).
- The output is open collector, so it needs a pull-up resistor; without one it never goes high (source: link, PDF p.2).
- It is unipolar: it is the magnetic field polarity and strength that switch it, so a magnet turned the wrong way may do nothing (source: link, description, PDF p.2). Allegro lists the part as discontinued, so module behaviour may differ.
Not covered by the official source
- Allegro marks the A3144 discontinued (Oct 2005) and recommends the A1104; the module's actual chip is not verified.
- Module board not documented by an official source.
Sources
- link (A3141-A3144 Sensitive Hall-Effect Switches, Allegro 27621.6B; discontinued product)