This product is for development and learning purposes only, not a consumer product, electronic purchase for use, requires microcontroller or FOR R3 development experience.

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AD8232 Sensor Module

Single lead heart rate monitoring front end

The AD8232 is an integrated front-end for signal conditioning of cardiac bioelectric signals for heart rate monitoring.

The AD8232 is an integrated front-end for signal conditioning of cardiac bioelectric signals for heart rate monitoring.

An integrated signal conditioning module for ECG and other bioelectric measurement applications. The device is designed to extract, amplify and filter weak bioelectric signals in the presence of noise generated by motion or remote electrode placement. The design allows the output signal to be easily captured by an ultra-low power analog-to-digital converter (ADC) or embedded microcontroller.

The AD8232 uses a bipolar high-pass filter to eliminate motion artefacts and electrode half-cell potentials. The filter is tightly coupled to the instrumentation amplifier structure, allowing for single-stage high gain and high pass filtering, resulting in space and cost savings.

The AD8232 uses an unused constrained operational amplifier to create a three-pole low-pass filter, eliminating additional noise. The user can select all filter cut-off frequencies to meet the needs of different types of applications.

To improve common mode rejection performance at system line frequencies and other undesirable interference, the AD8232 has a built-in amplifier for driven lead applications such as right-hand drive (RLD).

The AD8232 includes a fast recovery feature that reduces the otherwise long build-up long tail of the high-pass filter. If there is a sudden signal change in the amplifier rail voltage (e.g. a lead disconnect situation), the AD8232 will automatically adjust to a higher filter cut-off state. This function allows the AD8232 to achieve a fast recovery and therefore a valid measurement value as soon as possible after the lead is connected to the electrode of the measurement object.

The performance is guaranteed over a nominal temperature range of 0 °C to 70 °C and an operating temperature range of -40 °C to +85 °C.

Applications

Fitness and sports heart rate monitoring

Portable ECG

Remote health monitoring

Gaming peripherals

Bioelectric signal acquisition

Pin No. Pin Name Description

1 HPDRIVE High-pass driver output. The HPDRIVE should be connected to the capacitor in the first high-pass filter.

The AD8232 drives this pin to keep the HPSENSE at the same level as the reference voltage.

2 +IN Positive input to the instrumentation amplifier. +IN is normally connected to the left arm (LA) electrode.

3 -IN The negative input of the instrumentation amplifier. -IN is normally connected to the right arm (RA) electrode.

4 RLDFB Right leg drive feedback input. rldfb is the feedback pin for the right leg drive circuit.

5 RLD Right leg drive output. The drive electrode (usually the right leg) should be connected to the RLD pin.

6 SW Fast recovery switch pin. This pin should be connected to the output of the second high pass filter.

7 OPAMP+ Operational amplifier in-phase input.

8 REFOUT Output of the reference voltage buffer. The output of the instrumentation amplifier is referenced to this potential.

REFOUT should be used as a virtual ground for any point in the circuit where a reference signal is required.

9 OPAMP- Inverted input of the operational amplifier.

10 OUT Operational amplifier output. This output provides a fully conditioned heart rate signal.

OUT can be connected to the input of the ADC.

11 LOD- Lead-off comparator output. In DC lead off detection mode, when disconnected from the -IN electrode

LOD- is high when disconnected from the -IN electrode and low vice versa. In AC lead-off detection mode, LOD- is always low.

Lead off comparator output. In DC lead-off detection mode, LOD+ is high when the +IN electrode is disconnected and low when the +IN electrode is disconnected.

LOD+ is low when the +IN electrode is disconnected and vice versa. In AC lead-off detection mode, LOD+ is high when the -IN or +IN electrode is disconnected and low when both electrodes are connected.

When both electrodes are connected, LOD+ is low.

12 LOD+

13 SDN Off control input. Drive SDN low to enter low power shutdown mode.

14 AC/DC lead off mode control input. For DC lead off mode, the AC/DC pin should be driven low.

For AC lead off mode, the AC/DC pin should be driven high.

15 FR Fast Recovery control input. Driving FR high enables fast recovery mode; otherwise, it should be driven low.

16 GND Power ground.

17 +VS Power supply pin.

18 REFIN Reference voltage buffer input. REFIN (high impedance input pin) can be used to set the level of the reference voltage buffer.

19 IAOUT Instrument amplifier output pin.

20 HPSENSE High-pass detection input of the instrumentation amplifier.

HPSENSE should be connected to the R and C junctions that set the turn frequency of the isolation circuit.

EP Exposed pad. The exposed pads should be connected to GND or left unconnected.

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