TeleHealth Hardware

  This page is part of the OLPC Health Project. Hardware | Software | Content | Health Jam

Introduction

There are currently several groups working on Health sensors for the XO. Some are a simple as a temperature gauge that can be plugged into the audio-in port and used with Measure. But the eventual goal of Health Hardware is a $10USD USB device that can act as a full TeleHealth remote sensor package for pulse, temperature, blood oximeter, and many other simple sensors. This along with built in tools like the Webcam and Microphone it will allow doctors and Health Professionals to diagnose patients from hundreds of miles away. This would greatly stretch the abilities of limited resources for healthcare.

Three main use cases are envisioned for the project.

1. Stationary medical monitoring - in an impoverished ICU, Hospital, or as part of a check-up in a doctor's office
2. Remote checkups, multiplexing doctors' labor via non-realtime data viewing and allowing for simple algorithm sieves to be applied to parameterized data to flag individuals with higher needs
3. Real-time checkups following a discharge from a medical institution where on-site checkups are prohibited or made difficult via distance; 2 weeks, 4 weeks, 2 months, 6 months....

Sensors

EKG

Simple 3 lead EKG for arrhythmia and trauma diagnosis. Also facilitates pedagogical exercises into

• Four parts:
  • Connection: Electrodes connecting device to person
  • Amplification: Multiplies the voltage of the heart's electrical signal into something computer-usable
  • Opto-Isolation: Protection circuits
  • USB ADC: Inputs data to the XO

• Main Chipset : The AD8541/2/4 series op-amps fulfill the target specs perfectly.

Target Specs

• Low frequency: -3 db @ 0.1 Hz
• High frequency: -3 db @ 45 Hz
• Patient leakage current: <10 µA with acquisition module connected (meets AAMI standard SCL 1278)
• Chassis leakage current: <100 µA (meets AAMI standard SCL 1278)
• Common mode rejection: 130 dB minimum with balanced leads. With 5Kohm imbalance 100dB

• A/D conversion: 10-12 bits
• Impedance: 100 Mohm, defibrillator-protected (optional for the XO)
• Signal Dynamic range: 10 mV
• Electrode offset tolerance: + - 320 mV dc (this is due to the fact the electrodes get polarized)

• EKG Schematic Tentative design similar to the above specs
• EKG Circuit A photo of the initial circuit.

Status

• Current problems include tuning op-amps and prototyping.
• Determine efficient alternatives to the classical electrodes.

Pulse Oximeter

An invaluable piece of medical equipment relaying information about pulse and oxygen saturation by analyzing the output of two filtered photo-diodes in two different frequencies. The pulse oximeter operates on the theory that oxygenated and deoxygenated hemoglobin have different absorption and reflection frequencies. The same principle can be applied to any other small organic molecule with identifiable spectra, with proper calibration.

Hardware

Currently nonfunctional design consists of a MAX4006 photodiode signal amplifier connected to a photodiode. A red and IR Led are driven by the MCU alternately. The data from the photodiode will be transmitted to the XO and collated, where, after calibration, it will provide information in both graphical waveforms and numerical statistics.

• Main Chipset: MAX4006 Op-Amp

Problems

• Working with a SOT23 part with less than optimal tools

Stethoscope

A simple microphone and audio amplifier to pick up heart, lung and bowel sounds.

Hardware

• Button Mic
• Audio amplifier
• Shielded twisted-pair cable
• Mic plug

Status

• Requirements Identification

Thermometer

A small temperature monitor with accuracy of plus or minus half a degree Celsius will, with calibration, provide information about the body's natural temperature fluxes as well as alerting a monitoring individual to dangerous extremes.

Hardware

• MCP9700A Temperature Monitor in TO-92.
• Non-insulative casing for probe.

Status

• Prototyping

MCU + ADC

Following information may be obsolete - the ATtiny461 may be used instead, specs to follow

• The PIC18F4553, a derivative of the PIC18F4550, a commonly used MCU, is likely going to be used. Our current design borrows heavily from the CREATE USB Interface.
• The '18F4553 provides the following:
  • USB
  • 13x12b ADC
  • I2C
  • 40 pin DIP
  • 32KB of Flash Memory
  • Socketable DIP
• Design / Programming goals
  • Total of 7 digital outputs; 1 IR LED, 1 Red LED, and 5 Indicator LEDs
  • More than 6 analog inputs, voltage input ranging from 0-5v
  • Real-time reading of analog inputs via USB
    • Python or shell
  • Real-time reading of digital inputs via USB
    • Python or shell
  • Minimize number of unused pins / maximize hackability.
  • Firmware Bootloader supporting flash update via USB.
    • Software controlled? (Two digital outputs trigger reset and program buttons via transistor switching?)

• User:Mchua will likely be handling the /Programming.

Power Supply

Due to the nature of medical instrumentation as necessitating high-precision power supply, some combination of a regulator chip, fuse, and smoothing capacitor are needed. If the power supply of the circuit is connected to the electrical net, this has to be carefully isolated form the electrical connections that provide the biomedical signals. A bad isolation can put the patient at risk for electrical shock.

Hardware

• Main Chipset: LP2982
• LP2982 5, 4.5, or 3v regulator
• Over-voltage protector
  • Fuse
• USB Connector
• Shielding

Get Involved

Your help is very welcome in this project. If you would like to participate in the Health Jam in Seattle around early April we are looking for organizers and participants. Contact Ian Daniher if you're interested.

Help wanted

• Provide talent, time, or treasure:
  • If you have experience designing medical instrumentation, and are willing to mentor or assist high school age students...
  • If you have extra time and are able to send emails, track down sample components, or raise awareness...
  • If you don't know what to do with your old soldering iron, oscilloscope, or components collection...
• Program! We're in need of interested Python programmers.
• Provide expertise! Provide a critique of the procedure and component selection outlined above. We can always use an extra head, especially if you have any experience in the fields of telehealth or telemedicine
• Come to the Health Jam in Seattle, or help us plan it.

Parts needed to start developing

If you want to contribute to hardware or firmware design, you'll need the following to get started.

• Pre-Alpha BOM
• PIC Programmer

People

Ian Daniher has been working on designing (and learning everything needed to design) a TeleHealth Module for several months. He is doing parts selection, circuit design and layout, and general coordination type things.

Mel Chua is the firmware coder, and is organizing a Health Jam in April to complete the project

Seth Woodworth is the man on the ground in Seattle getting resources organized for the upcoming Health Jam

Similar Projects

• http://reza.net/cms/index.php?page=HealthMonitor
• http://www.thinkcycle.org/tc-notes/?topic_id=39823
• http://web.media.mit.edu/~msung/vitamon.php

P.S. and random thoughts

• Optimize design for low part count, reducing complexity, allowing for field repair.
• Multipurpose chips? Potentially share op-amps between EKG and Pulse ox.
• Water and sterilizer proof case - allow for submersion in alcohol to sterilize?