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One Technology Way · P.O. Box 9106 · Norwood, MA 02062-9106 · Tel: 781.329.4700 · Fax: 781.461.3113 · www.analog.com

Rev 03 Jan 2013 19:42 | Page 1

AD8232 EVALUATION BOARD

DOCUMENTATION

FEATURES

Ready to use Heart Rate Monitor (HRM) Front end

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Accepts 2 or 3 electrode options

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Directly interface to data acquisition or ADC

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Access features with switch jumpers

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Allows various circuit configurations

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Figure 1.

GENERAL DESCRIPTION

The AD8232-EVALZ contains an AD8232 Heart Rate Monitor Front End conveniently mounted with the

necessary components for initial evaluation in fitness applications. Inputs, outputs, supplies and other

circuit test points have been routed to vector pins to simplify connectivity to test clips and probes.

Switches and jumpers are available for setting the input common-mode, shutdown (SDN), fast-restore

Summary of content (10 pages)

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One Technology Way · P.O. Box 9106 · Norwood, MA 02062-9106 · Tel: 781.329.4700 · Fax: 781.461.3113 · www.analog.com AD8232 EVALUATION BOARD DOCUMENTATION FEATURES ● ● ● ● ● Ready to use Heart Rate Monitor (HRM) Front end Accepts 2 or 3 electrode options Directly interface to data acquisition or ADC Access features with switch jumpers Allows various circuit configurations Figure 1.
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(FR), and AC/DC leads-off detection. QUICK START The board ships with a default configuration for three-electrode systems connected to the hands. Ensure that the switches and jumpers are set to the default values shown in Table 1. For two-electrode configurations, the settings are shown in Table 2. TABLE 1.
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Note that the electrode interfaces +VIN, -VIN and RLD are equipped with 180kΩ and 499kΩ (R6, R7 and R1 respectively) resistors to limit current injection to the subject in the event of fault or overload. Please note that these will not protect against supply line transients coming through the system. Isolation from the power line is always required when connecting to a live subject.
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Figure 3. AD8232-CHARZ Board Simplified Schematic (Refer to Figure 12 for complete version) Right-Leg Drive Amplifier The integrated right-leg drive (RLD) amplifier senses the common mode voltage present at the signal inputs and can drive an opposing signal into the patient. This driven electrode functionality maintains the voltage between the patient and the AD8232 constant, greatly improving the common mode rejection ratio.
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FILTER DESIGN The resistor and capacitor values for the filters were selected to provide effective noise rejection in applications that involve pulse detection while the subject is in motion. The filter parameters can be adjusted to fit other applications. High-Pass Filters The instrumentation amplifier in the AD8232 applies gain and high pass filtering simultaneously. This capability allows it to amplify a small ECG signal by 100 while rejecting electrode offsets as large as ±300 mV.
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subsequent low pass filter. The component values selected on the evaluation board yield good results without the need of a buffer. Keep this in mind when changing component values. Low-Pass Filter The internal uncommitted op amp is used to build a two-pole low pass filter with gain, using a Sallen-Key configuration. The following design equations set the low-pass cut-off frequency, gain and Q.
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Additional Low-Pass Filters The components R14, C13, R19 and C15 offer additional filtering options. The pin labeled VFILT is located after the first filter (R14 and C13). The pin labeled VFILT2 is located after both filters. LEADS-OFF DETECTION The AD8232 includes leads off detection features. It provides modes optimized for either two or three-electrode configurations. DC Leads-Off Detection To use this mode, the switch position must match the text labeled as “DC” on the silkscreen.
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and therefore take valid measurements soon after connecting the electrodes to the subject. To access this function, set the jumper P2 connection between pins 1 and 2. To disable, connect pins 2 and 3. BOARD SETTINGS FOR TWO ELECTRODE CONFIGURATION The AD8232-CHAR-Z can be configured to suit two-electrode applications, as shown in Table 2. TABLE 2.
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does not create resistive parasitic paths In-Amp High Pass Filter: C6, R9 The cutoff frequency is set to 7.2Hz. Refer to the High-Pass Filters section for more information AC-Coupling: C9, R11 The cutoff frequency of this high-pass filter is set to 7.2Hz. Because this is a DC-blocking circuit, connecting R11 to the REFOUT voltage is necessary to allow negative signal swings.
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Differential signal cutoff frequency: 1/(2πR(2×C4 + C)) Lower common mode signal cutoff frequency will improve RFI rejection, but may increase the risk of instability with a right leg drive feedback loop After any solder work in the RFI filter area, the board should be thoroughly cleaned so that residual flux from the soldering does not create resistive parasitic paths. EVALUATION BOARD SCHEMATIC CLICK ON THE PICTURE TO SEE A LARGER VERSION © Analog Devices, Inc. All rights reserved.