Texas Instruments European Analog Design Contest 2013 ...

Texas Instruments European Analog Design Contest 2013 Project Report

iToilette

Team Leader: Alexander Beckmann,

Team Members:Team Sebastian Peters,
Sabine Wingenbach,
Melanie Schutz,

Advising Professor: Univ.-Prof. Dr.-Ing. Dr. med. Steffen Leonhardt,

University: RWTH Aachen University, Germany

Date: 30.07.2013

Qty. TI Part Number & URL Qty. TI Part Number & URL

1 MSP430 F5437A 1 TPS63001

1 AFE4300

Abstract:
The iToilette is a medical device for discrete, regular and automatic monitoring of a patients
vital signs. When sitting on the toilet, the patient's weight is measured by sensors beneath
the seat. With electrodes on the seat surface, the bioelectrical impedance is measured at
the patient’s bottom. The bioelectrical impedance analysis is a method that has been
gaining importance in recent years. With the measurements it is possible to draw
conclusions on the total body water, the fat free mass, the fat mass and the body cell mass.
The toilet was chosen as the ideal location of this monitoring, as it is already visited several
times a day. The installation of an iToilette into a patient’s toilet is simple, transparent and
provides the patient with a comfortable increase in security. TI low-power components allow
a safe, compact and battery-operating design.

Introduction

We live in a time of increasing cross-linking. The Internet is no longer a second
parallel world, but integrates more and more into our everyday lives. It started with
navigation systems to give us directions and by now it connects our refrigerators,
washers and athletic footwear. Those things save time, simplify our lives and provide
us with many other services.

In our project we dealt with the collection of vital data for the improvement of the
patient’s health and preventive health care. We took the integration into everyday
live very seriously and therefore integrated our measuring device into a toilet.

The collection of vital signs data is a very important field of application in regard of
the increasing world population, increasing numbers of diseases caused by
civilization as well as increasing health care costs.

The project name “iToilette” is derived from “intelligent” and “Toilette”, the German
word for toilet.

Motivation for the project

Bioelectrical impedance analysis is a highly up-to-date and exciting way to constantly
capture a lot of important data on the vital status of a patient by four body contacts.

First, there was an idea followed by the opportunity to realize the construction by
making use of the equipment that the Helmholtz-Institute for Biomedical Engineering
provides and finally the TI AFE4300 that helped integrating our circuit for
measurements.

Theoretical background

Bioelectrical impedance analysis
The resistance of the human body is measured using an alternating current of
375μArms at a frequency between 1kHz and 500kHz. With two electrodes, an
electromagnetic field is built up in the human body. With two other electrodes within
this field, the voltage drop and the phase shift of the signal voltage is measured. One
single measurement of a patient is less significant than a series of measurements
over a longer period of time which shows changes in the body's composition. The
measurement position at the back of the thighs is different from the “official”
measurement position (hand and foot), but works, too. The BIA is affected by
dehydration, sports and food.

Weight measurement
Weight measurement in commercial personal
scales works with a Wheatstone bridge circuit.
Up to four strain gauges (DMS) are connected
in a circle. Each DMS consists of two parts:
Under external pressure one is stretched and
the other one compressed. The orange circles

in the right diagram show the actual components. They have to be connected in such
a way that DMS 1 and 3 are stretched and 2 and 4 are compressed or the other way
around. A typical resistance value for one DMS is at about 1000 ohm. U_bat is
typically at about 1.7V. U_sig is at about 1mV.

Medical background
Patients with right heart failure have a weak right heart. Their blood accumulates in
front of the heart and pushes back into the body circulation. The liquid constituents
of the blood are forced out of the blood vessels in the body tissue. This causes water
retention: edemas.

Sufferers of right heart failure often first notice an increase in weight through the
water in the cells. We distinguish acute from persistent chronic heart failure. The
acute heart failure develops over hours to days, while chronic heart failure develops
over months to years. Both can be detected by regular weight and bio impedance
measurement.

Patients with diabetes or obesity have to stick to strict diet. They need a regular
feedback signal. Changes in their weight or their body composition can be important
clues to the disease running.

Implementation

Toilet seat
The iToilette is based on an inexpensive
wooden toilet seat from retail. We have
extended the seat with a substructure, which
is essential for weight sensors. The sensor
cables are routed to the rear.

Electrodes
The electrodes for bioelectrical impedance
analysis are made by conducting silver
lacquer at four positions around the seat. On the bottom they are connected by
soldered cables. An important advantage of such painted electrodes is that no
bacteria can accumulate in spaces which are inevitable when using electrode plates.
The visible side is galvanically gold plated in the tampon procedure.

The tampon procedure is a processing
technology to galvanize without using an
electrolyte bath. It uses an anode with an
absorbent sponge full of gold electrolyte. The
cathode is our future electrode. Parts of any
type can be either partially or fully galvanized.

As can be seen in the right picture, the result
was not visually perfect. This was presumably
due to poor gold electrolyte.

Gold was used for the electrodes because it is optimal for medical application. It
does not oxidize like silver or cause allergies like nickel. Contact to a patient’s skin is
totally safe.

Weight sensors
The four weight sensors were placed between the seat and a substructure. They are
strain gauges – resistors that change their resistance to pressure. These metal
flakes are sunk in the wood using a CNC mill. The tape was used simply to protect
the electrodes bottom.

A footboard is planned and sensible to make sure that the entire weight of the patient
is measured. At the institute we were able to borrow a footboard for testing purposes.
It was not developed by us.

Circuit design
The following block diagram shows the structure of our components. The framed part
is optional and solely important for development. It will be eliminated in the finished
product.

UART

USB

PC FT232 MSP430

SPI Power TPS 63001

AFE4300

electrodes weight-measurement
bridge

AFE4300
“The AFE4300 is a low-cost analog front-end incorporating two separate signal

chains: one chain for weight-scale (WS) measurement and the other for body
composition measurement (BCM) analysis.” (Description from www.ti.com)

This chip is the heart of our circuit. It integrates bioelectrical impedance analysis and

weight-measurement. Without the AFE, both measurements could only be

implemented with considerable circuitry overhead.

MSP430
The TI MSP430 (MSP430F5437A) is a 16-Bit Ultra-Low-Power Microcontroller with
16-bit RISC CPU, 16-bit registers, three timers and A/D converter.

In the current revision of the circuit the MSP only passes the measured data from the
AFE to the FT232 USB chip on. For future versions it is planned that the MSP does
the analysis of the data which is currently done by a C# application on a computer all
on its own.

TPS63001
The TPS63001 provides a power supply solution based on NiCd, NiMH, Li-Ion or Li-
polymer batteries. It enables a battery operating and portable system. At the moment
a one-cell Li-Ion battery is used for power supply. The TPS provides 3.3V output
voltage and output current up to 800mA. At first glance it is a little oversized, but a
look at the efficiency chart shows an efficiency of about 70% at 1mA. This is
perfectly fine for our circuit and the Li-
Ion battery. It allows us to expand the
circuit as desired without having to
worry about the power supply.

PC Application
At the moment the computer frontend
is a technically looking graphical user
interface written in C#. It opens a
COM Port and communicates via USB
with the FT232 to get single results of
weight-scale measurement or body
composition measurement.

Patient safety
The norm IEC 60601-1 is necessary for medical electrical equipment transferring
energy to or from the patient. A measurement showed that the AFE measures with
only 250µArms. In the data sheet is written:
“The resistor and the DAC amplitude are set so that the current injected is 375
μArms when all the elements are nominal. With a +20% error, the source is
450μArms, and still below the 500μArms limit.” (AFE4300, page 14)
In addition, the circuit includes DC blocking capacitors, which protect from DC
currents. For the use with patients it needs a safety circuit with emergency shutdown
preventing high currents flow through the patient in case the chip burns out.

Experimental results

Weight measurement
The weight measurement is working properly and the measured data of the first
series of measurements are as follows.

Real weight (kg) measurement without offset scaling factor

0 700 0

2,9 1130 430 0,00674419

1,5 920 220 0,00681818

9,3 1809 1109 0,00838593

4,1 1260 560 0,00732143

6,6 1655 955 0,00691099

12 2222 1522 0,00788436

84,3 6050 5350 0,01575701

0,00854601 (average)

The offset apparently comes from the weight of the seat and/or from the sensors
themselves. The scaling factor can be used for a linear approximation of the form
f(x)= mx + b, but the following graph rather indicates a root curve of the form
f(x)=sqrt(x*340000)+700. An apparent weak point of the measurement is the lack of
results in the range 20kg to 70kg. Nevertheless, we still expect the root curve.

7000 y = 60,262x + 1059
6000 10 20 30 40 50 60 70 80 90
5000
4000
3000
2000
1000

0
0

Bioelectrical impedance analysis
Many problems with the AFE made it hard to capture usable data. In addition, it is
not safe to use humans for testing purposes (see patient safety above).

resistors real value measurement 1kHz measurement 10kHz measurement 100kHz

RP0|RN0 (ohm) value value/real value value/real value value/real
RP0|RN1
RP1|RN0 99,4 214 2,152917505 690 6,9416499 52 0,523138833
RP1|RN1
extern 200 958 4,79 2704 13,52 2336 11,68

700 144 0,205714286 392 0,56 1212 1,731428571

953 4492 4,713536201 13062 13,706191 11400 11,96222455

1000 3192 3,192 7058 7,058 7064 7,064

Impedance analysis is only partly working. While we are able to generate a sine
signal and apply it to the calibration resistors, the results are incoherent. With two of

the calibration resistors, we get the same scaling factor. However, it does not fit the
other resistors. This hints to an issue with the circuits which unfortunately remains
unresolved.

Conclusions/Summary

Specific:
 Weight measurement is working properly and should be implemented next on
the MSP instead of the C# Application on PC.
 Bioelectrical impedance analysis does not satisfy yet, but should work
properly after a day of adjusting.
 One next step is to implement continuous measurement series.

General:
 Dealing with vital data is more exciting than dealing with “dead” things
 Everything took longer than expected
 We hope that we or others at the Institute will find time for further
development of the iToilette

Our vision

In the near future the iToilette will be standard equipment in every hospital and - in
not too distant future - in every household. The iToilette captures all vital data
including an electrocardiogram, blood pressure, body temperature and respiratory
rate. The collected data are transmitted to a medical server, associated with the
correct patient and with the vital data from the sensors in the patient’s clothes and
the patient’s bed.

Diseases and health risks are detected early and can be preemptively prevented!

Bill of materials

Part Value Device Package
PINHD-1X7 1X07
AFE PINHD-1X2 1X02
BATTERY_
POWER 100n C-EUC0805 C0805
C1 100n C-EUC0805 C0805
C2 4.7µ C-EUC0805 C0805
C3 100nF C-EUC0805 C0805
C4 470n C-EUC0805 C0805
C5 470n C-EUC0805 C0805
C6 1u C-EUC0805 C0805
C7 10n C-EUC0805 C0805
C8 100n C-EUC0805 C0805
C9 C-EUC0603 C0603
C10 100n C-EUC0805 C0805
C11 C-EUC0603 C0603
C12 1u C-EUC0805 C0805
C13 10u C-EUC0805 C0805
C14 10u C-EUC0805 C0805
C15 100n C-EUC0805 C0805
C16 100n C-EUC0805 C0805
C17 100n C-EUC0805 C0805
C18 100n C-EUC0805 C0805
C19 100n C-EUC0805 C0805
C20 100n C-EUC0805 C0805
C21 100nF C-EUC0805 C0805
C22 100nF C-EUC0805 C0805
C23 100nF C-EUC0805 C0805
C24 100nF C-EUC0805 C0805
C25 100nF C-EUC0805 C0805
C26 100nF C-EUC0805 C0805
C27 CGRM4001-G CGRM4001-G SOD-123_MINI-SMA
D1 CGRM4001-G CGRM4001-G SOD-123_MINI-SMA
D2 PINHD-1X2 1X02
EXT_POWER FT232RL FT232RL SSOP28
IC1 TPS6300 TPS6300 DRC-S-PVSON-N10
IC2 AK500/2-H AK500/2-H
INM1/GND AK500/2-H AK500/2-H
INM2/GND AK500/2-H AK500/2-H
IOUT0/1 PINHD-1X3 1X03
JP2 PINHD-1X3 1X03
JP4 ML14 ML14
JTAG

L1(COIL_NOT_R) 2,2µH R-EU_R0603 R0603
MSP/USB PINHD-1X7 1X07
MSP430F5437A MSP430F5437 F54XX---PN80 PN80
QG1 XO91 CRYSTAL XO91
25,0MHz RESONATORXO91
QG2 FXO-HC536R- CRYSTAL XO53
1 RESONATORXO53
R1 499 R-EU_R0805 R0805
R2 100k R-EU_R0805 R0805
R3 10k R-TRIMMT93YA RTRIMT93YA
R4 10M R-EU_R0805 R0805
R6 10k R-EU_R0805 R0805
R7 10k R-EU_R0805 R0805
R8 10k R-EU_R0805 R0805
R9 10k R-EU_R0805 R0805
R10 10k R-EU_R0805 R0805
R11 200 R-EU_R0805 R0805
R12 750 R-EU_R0805 R0805
R13 100 R-EU_R0805 R0805
RESET JP1E JP1
U$2 AFE-4300- AFE-4300-TQFP-
TQFP-80S- 80S-PQFP-G80 AK500/2-H
VLDO/INP1 PQFP-G80 AK500/2-H
VLDO/INP2 AK500/2-H AK500/2-H
VSNS0/1 PN61729-S AK500/2-H PN61729-S
X1 AK500/2-H
PN61729-S