Abstract—During medical procedures, such as surgery, a
patient's vital signs are typically monitored using a web of
wires connected to adhesive electrodes. The large number of
wires inhibits the medical team's access to the patient while the
adhesive electrodes can detach, fail, or be out-of-stock, causing
delays in the procedure. In order to combat these problems,
we have developed the SmartPad: a system that displays a
patient’s electrocardiogram (ECG) signal without adhesive
pads, wires, or active intervention from a clinician. The system
automatically selects three electrodes from an array of Cu/Ni-
fabric based electrodes patterned on a thin pad on which the
patient lies. The selected electrodes are used to provide a
differential 3-lead measurement of the patient’s ECG, which is
then transmitted wirelessly and displayed on a laptop
computer.
I. INTRODUCTION
n the ambulance, the operating room, and the intensive
care unit, patient vital signs are obtained through various
wires and adhesive electrodes attached to the patient [1].
The large number of wires inhibits the medical team's access
to the patient, and in traumatized or burned patients, the
adhesive pads will not stick to burns or bloody surfaces.
Furthermore, in ambulances or other austere care sites, pads
and leads must be stocked and resupplied.
Previous works addressing the need for unobtrusive ECG
signal acquisition have primarily focused on low-cost
mobile monitoring systems [2-5], and electrode technology
for skinless contacts [6-8]. However, neither approach can
be a low-cost replacement for current disposable electrodes
and both require some level of human interaction to either
place or determine the appropriate electrodes to use. Mobile
monitoring systems still require precise placement of
adhesive pads while skinless contact solutions require

Manuscript received April 6, 2008. This work was supported in by the
Center for Integration of Medicine and Innovative Technology.
F. Chen is with the PhD Program in Electrical Engineering at the
Massachusetts Institute of Technology, Cambridge, MA 02139 USA (e-
mail: fredchen@mit.edu).
H. Wu is with the Master’s Program in Electrical Engineering at the
Massachusetts Institute of Technology, Cambridge, MA 02139 USA.
P. Hsu is with the Master’s Program in Electrical Engineering at the
Massachusetts Institute of Technology, Cambridge, MA 02139 USA.
B. Stronger is with the Department of Mechanical Engineering at the
Massachusetts Institute of Technology, Cambridge, MA 02139 USA
R. Sheridan is with the Shriner’s Hospital Children Boston and the
Massachusetts General Hospital, both in Boston, MA 02114 USA
H. Ma is with the Department of Electrical Engineering at the
Massachusetts Institute of Technology, Cambridge, MA 02139 USA (e-
mail: hongma@mit.edu)
relatively large electrodes that may not be suitable for
certain patients such as children. Although an unobtrusive
ECG measurement through clothing has been demonstrated
[7], it requires active circuitry at the electrode end and does
not address the problem of determining the proper electrodes
to use.
To address these issues, we have developed the SmartPad
system which automatically detects and selects the optimum
electrodes to use from an array of electrodes patterned on a
pad, and thus obviates the need for manual intervention.
This electrode selection algorithm also allows the SmartPad
system to select the electrode contacts as the patient shifts
position or is transported. Combined with a low-cost
electrode interface and wireless data transmission, the
SmartPad system displays a patient’s ECG signal without
the need for adhesive pads, wires or any human intervention.
II. SYSTEM DESCRIPTION
The SmartPad system schematic, shown in Fig. 1, is
comprised of an array of electrodes connected to an analog
multiplexing network followed by a three-lead ECG circuit
consisting of amplifying, filtering, and sampling stages. The
digitized data is transmitted to an application program
running on a laptop. Communication between the ECG
circuitry and the laptop can be either a ZigBee wireless link
or a USB wired link.
Off-the-shelf hardware is used to implement various
components of the system including an MSP430
microcontroller, an INA118 instrumentation amplifier,
OPA340 op-amps, and SN74LVC2G66 analog switches (all
from Texas Instruments). The RS232 transmission from the
MSP430 is handled using either a FT232 chip (FTDI),
which provides USB connectivity, or an XBee radio module
(Maxstream), which provides ZigBee wireless connectivity.

Patient
Sensor 
Multiplexing
Laptop Software: 
Signal Processing and Sensor 
Optimization
ECG
Circuit
Wireless
USB


Fig 1. SmartPad system-level description

SmartPad: A Wireless, Adhesive-Electrode-Free,
Autonomous ECG Acquisition System
Fred Chen, Student Member, IEEE, Henry Wu, Pei-Lan Hsu, Brad Stronger, Robert Sheridan, and
Hongshen Ma
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