AD8232 ECG front end: specs and pinout
A single-lead heart rate monitor front end built around the Analog Devices AD8232. It amplifies and filters a small electrical signal from skin electrodes. For learning and prototypes only, not a medical device.
Safety note. For learning and prototypes only, not a medical device. Never connect electrodes to a person while the circuit is powered from mains or from a computer plugged into mains; use a battery or USB power bank.
Specs
| Spec | Value | Source |
|---|---|---|
| Supply range | 2.0 V to 3.5 V | source Table 1 System specifications, Supply Range (p.4); features (p.1) |
| Absolute maximum supply voltage | 3.6 V | source Table 2 Absolute Maximum Ratings (p.5) |
| Quiescent supply current | 170 uA typ, 230 uA max | source Table 1 System specifications (p.4) |
| Instrumentation amplifier gain | 100 V/V | source Table 1 (p.3) |
| Common-mode rejection ratio, dc to 60 Hz | 80 dB min, 86 dB typ | source Table 1 (p.3) |
| DC differential input range | -300 mV to +300 mV | source Table 1 (p.3); features accept up to 300 mV half-cell potential (p.1) |
| Operating temperature range | -40 C to +85 C (specified performance 0 C to 70 C) | source Table 1 System specifications (p.4); Table 2 (p.5) |
| Leads-off detection | DC mode (AC/DC pin low) or AC mode (AC/DC pin high), outputs LOD+ and LOD- | source Table 3 pins 11, 12, 14 (p.6) |
Power
| Value | Source | |
|---|---|---|
| Supply | 2.0-3.5 V single supply; designed to run from a single 3 V battery such as a CR2032 | source Table 1 (p.4); Power Supply Regulation and Bypassing section |
| Current | 170 uA typ (230 uA max) | source Table 1 (p.4); Power Supply Regulation and Bypassing section |
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.
The pin table is for the bare AD8232 chip (20-lead LFCSP). The module board's header labels, regulator and electrode connector are not covered by an official document, so no module labels are given.
| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| 1 HPDRIVE | High-pass driver output; connect to the capacitor in the first high-pass filter | source Table 3 Pin Function Descriptions (p.6) | ||
| 2 +IN | Instrumentation amplifier positive input | Typically the left arm (LA) electrode. | source Table 3 Pin Function Descriptions (p.6) | |
| 3 -IN | Instrumentation amplifier negative input | Typically the right arm (RA) electrode. | source Table 3 Pin Function Descriptions (p.6) | |
| 4 RLDFB | Right leg drive feedback input | source Table 3 Pin Function Descriptions (p.6) | ||
| 5 RLD | Right leg drive output; connect the driven electrode (typically right leg) | source Table 3 Pin Function Descriptions (p.6) | ||
| 6 SW | Fast restore switch terminal; connect to the output of the second high-pass filter | source Table 3 Pin Function Descriptions (p.6) | ||
| 7 OPAMP+ | Operational amplifier noninverting input | source Table 3 Pin Function Descriptions (p.6) | ||
| 8 REFOUT | Reference buffer output; use as virtual ground for any point needing a signal reference | source Table 3 Pin Function Descriptions (p.6) | ||
| 9 OPAMP- | Operational amplifier inverting input | source Table 3 Pin Function Descriptions (p.6) | ||
| 10 OUT | Operational amplifier output; the conditioned heart rate signal, can go to an ADC | source Table 3 Pin Function Descriptions (p.6) | ||
| 11 LOD- | Leads off comparator output | DC mode: high when the -IN electrode is disconnected. AC mode: always low. | source Table 3 Pin Function Descriptions (p.6) | |
| 12 LOD+ | Leads off comparator output | DC mode: high when the +IN electrode is disconnected. AC mode: high when either electrode is disconnected. | source Table 3 Pin Function Descriptions (p.6) | |
| 13 SDN | Shutdown control input; drive low for low power shutdown | source Table 3 Pin Function Descriptions (p.6) | ||
| 14 AC/DC | Leads off mode control input; low for DC mode, high for AC mode | source Table 3 Pin Function Descriptions (p.6) | ||
| 15 FR | Fast restore control input; drive high to enable fast recovery, otherwise low | source Table 3 Pin Function Descriptions (p.6) | ||
| 16 GND | Power supply ground | source Table 3 Pin Function Descriptions (p.6) | ||
| 17 +VS | Power supply terminal | source Table 3 Pin Function Descriptions (p.6) | ||
| 18 REFIN | Reference buffer input, high impedance; sets the reference buffer level | source Table 3 Pin Function Descriptions (p.6) | ||
| 19 IAOUT | Instrumentation amplifier output terminal | source Table 3 Pin Function Descriptions (p.6) | ||
| 20 HPSENSE | High-pass sense input for the instrumentation amplifier; connect to the junction of R and C that sets the high-pass corner | source Table 3 Pin Function Descriptions (p.6) |
Build with it
Project ideas for the AD8232 ECG front end. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.
- ECG waveform viewer: Prototype for learning, not a medical device. The chip runs at 2.0-3.5 V, so the ESP32's 3.3 V fits; read OUT on an ESP32 ADC pin and draw the trace. Power it from a USB power bank only, with the laptop unplugged from mains, and never connect a person while any part of the circuit is powered from mains.
- Electrode contact indicator: Prototype for learning, not a medical device. LOD+ and LOD- go high when an electrode is disconnected (DC mode), so two LEDs can show which lead is loose. Each LED needs a series resistor from the resistor pack. Use a power bank or battery only, with no mains-powered equipment connected while electrodes are on a person.
- Pico ECG trace on a small screen: Prototype for learning, not a medical device. The Pico has 3.3 V logic and an ADC for the OUT pin. Power from a USB power bank only; do not connect a person while the circuit is powered from mains or from a mains-powered laptop.
Common mistakes
- Powering the chip above its limit: the supply range is 2.0-3.5 V and the absolute maximum is 3.6 V, so a bare chip must not see 5 V (source: link, Tables 1-2). The module board's regulator is not covered by this sheet.
- Feeding it from a lithium-ion cell without a regulator: the voltage during charging can exceed the absolute maximum; the sheet recommends a power switch or a low-dropout regulator (source: link, Power Supply Regulation and Bypassing)
- Ignoring leads-off pins: in DC mode LOD+ is high when the +IN electrode is disconnected and LOD- is high when the -IN electrode is disconnected, so a flat trace can simply mean a loose electrode (source: link, Table 3 pins 11-12)
Not covered by the official source
- The Analog Devices sheet does not state a rule about mains-powered equipment. The 'battery or USB power bank only, laptop unplugged from mains' caution is a general caution, not sourced to the sheet. The sheet only says its example circuit is battery-powered and that medical safety compliance needs more work.
- Module board (regulator, header labels, electrode cable, filter values) is not covered by any official document.
- Pin numbers are for the 20-lead LFCSP chip, not the module.
- analog.com could not be reached from this machine, so the original maker's copy was used.
Sources
- link (Analog Devices AD8232 data sheet, Rev. A; verbatim copy hosted on a mirror)