This current sensor from Pololu is a carrier for Allegro’s ACS714LLCTR-05B-T Hall effect-based linear current sensor, which operates at 5V and has an output sensitivity of 185 mV per A. 

The current sensor board features:

• Bidirectional measurement from -5 to 5 V (though the robust sensor IC can survive up to five times the overcurrent condition).
• The sensor's conductive path internal resistance is typically 1.2 mΩ (just over 1/1000 of an ohm), and the PCB is made with 2-oz copper, so very little power is lost in the board.
• Use of a Hall effect sensor means the IC is able to electrically isolate the current path from the sensor’s electronics (up to 2.1 kV RMS). This means it can be used anywhere along the current path, and still offers good electrical isolation!
• 80 kHz bandwidth that can optionally be decreased by adding a capacitor across the board pins marked “filter”.
• High accuracy and reliability. With a typical total output error of 1.5% (at room temperature with factory calibration), an extremely stable output offset voltage, and almost zero magnetic hysteresis.
• Automotive grade operating temperature range of -40°C – 150°C.

The sensor requires a supply voltage of 4.5 – 5.5 V to be connected across the Vcc and GND pads, which are labeled on the bottom silkscreen. The sensor outputs an analog voltage that is linearly proportional to the input current. This output voltage is centered at 2.5 V and changes by 185 mV per amp of input current, with positive current increasing the output voltage and negative current decreasing the output voltage.

The input current can be connected to the board in a variety of ways. For low-current applications, you can solder 0.1" male header pins to the board via the small through-holes on the input-current side of the board. For higher-current applications, you can solder wires directly to the through-holes whose sizes best match your wires, or you can use solderless ring terminal connectors, as shown in the picture to the right. The large through-holes are big enough for #6 screws.

Mounting information

The board has two mounting holes on the logic side of the board. These mounting holes are 0.5" apart and are designed for #2 screws.

Filtering the output

The IC has an internal filter resistance of 1.7 kΩ, and the carrier board includes a 1 nF filter capacitor, which produces a low-pass RC filter with a 90 kHz cutoff. You can improve sensing system accuracy for low-frequency sensing applications by adding a capacitor in parallel with the integrated 1 nF capacitor across the pads marked “filter” on the bottom silkscreen (this capacitor is labeled C2b in the schematic below). The frequency F that the filter will attenuate to half its original power is given by:

F = 1 / (2πRC) = 1 / (11kΩ * (1 nF + Cf))

where Cf is the value of the capacitor added to the filter pads.

• [Data Sheet]: Allegro ACS714 Current Sensor Datasheet