ELECTRONICS AND HEALTH

In recent days, there has been an increase in the rate at which some uncommon ailments affect the normal life of people, and even death sometimes. Ailments such as hypertension, hypo-tension and stroke have been on the increase and many lives had been cut short due to sudden seizure of the health and increase in the body’s systolic and diastolic pressures. The victims of these ailments are caught unaware as to when the harmful effects of these ailments would be unleashed on them, and by the time the effect comes, they are put into a helpless condition.

This write up presents the design and development of a micro-controller based health monitoring device that can be used to measure some important health parameters of individuals. The mobile device encompasses a contact-less temperature and a pulse sensor from which the values of the blood pressure can be obtained. These sensors acquire the health beat and the temperature values by making use of the embedded software, save the values on the controllers memory, display the values on a Liquid Crystal Display for the user to see, and sends information about the status of the patient to the mobile number of the caretaker upon the press of a particular button via GSM modem.

This information about the users’ status is arrived at comparing the values read by the sensor with the medical standards.

Heart rate data can be really useful whether you’re designing an exercise routine, studying your activity or anxiety levels or just want your shirt to blink with your heart beat. The major concern is just that the heart rate can be difficult to measure, same thing with the blood pressure. Their values vary depending on the physical needs of the body, such as the necessity to intake oxygen. They also vary with the activity performed such as exercising or sleeping; the psychological state of a person also affects it, for example, if he/she is stressed, anxious, feeling ill, etc.

So, it’s necessary to have a mobile device that will keep track of these health parameters everywhere one is. This would help save the user of the harmful effects of the ailments already mentioned while it also put at ease; the medical prescription by the concerned medical personnel.

SYSTEMS DESIGN

The “Mobile Health Monitor” is classified basically into the hardware and software sections. The hardware section consists of the temperature and pulse detection units, the controller unit, the display unit and the GSM unit.

OPERATION OF THE STAGES

source: flickr

→Temperature Sensor- The MLX90614

is an infrared thermometer that can be used to measure temperature without physical contact with the body. It has within it an IR sensitive thermopile detector chip and signal conditioning circuits, both which are integrated in one TO-39 can. Aside these two, embedded within the sensor are 17-bit Analog-to-Digital Converter (ADC), a noise amplifier and a very powerful Digital Signal Processor (DSP).

This makes the sensor to have a higher accuracy and resolution.
The sensor comes factory scaled with a digital SMBus output thereby enabling the user to have maximum access to the measured temperature in the complete temperature range(s) with a resolution of 0.02°C.The user can configure the digital output to be pulse width modulation (PWM). As a standard, the 10-bit PWM is configured to continuously transmit the measured temperature in range of -20 to 120°C, with an output resolution of 0.14°C.

Interfacing of MLX90614 with the controller is quite easy and the user only needs to place his or her hands near the device to get the temperature values measured. It requires just two pins of the microcontroller: the SDA terminal of the sensor is interfaced with the SDA pin of the ATMEG328 (pin 27) and the SCL terminal is connected to the corresponding SCL (pin 28) of the microcontroller. The other two pins are the power pins: Vin and GND. Vin is given a minimum of 3.3.V and maximum of 5V while GND is connected momentarily to the ground.

flickr

→Pulse Detection- CNY70

Heart beat sensor is designed to give digital output of heart beat when a finger is placed on it. Heartbeat is sensed by using CNY70, a sensor made up of an optocoupler- a light source (an infrared) and light detector (a phototransistor) packed together in a single can. To measure the heartbeat, the user only needs to place his/her fingertip on these optocoupler. The light source in the sensor transmits an infrared signal to the finger, the very minute signal is the received by the light detector and made to pass through a stages of amplification as shown below:

proteus simulation: designed by me

As shown above, the CNY7O is powered by 5V, with a 220 ohm resistor limiting the flow of current entering the anode terminal of the sensor, and a 10kilo ohm resistor limiting the current flow to the collector of the sensor. This is the ideal way of connecting the sensor to voltage source. With this arrangement, one can only get approximately 4V as an output from the collector of the CNY70, which we call the threshold voltage (this is about 70% of the total 5V supplied). If we multiply 70% by 4, we would get 2.8V which equals 600 in analog to digital conversion (ADC). With this, the maximum ADC value the microcontroller can read is 600.
The output is connected to a 4.7uF electrolytic capacitor which helps filter noise components of the signal and the output is fed into a non-inverting LM324 amplifier operating at a gain of 101. The output from this amplifier is also fed to another LM324 amplifier where the final amplification is done. The output is the fed into a LM324 buffer amplifier, and from there to the controller. The whole process helps read the actual value of the heart rate.

credit: Wikipedia

→Microcontroller Stage- ATMEG328

Microcontrollers as the name suggests are small controllers. They are single chip computers that are often embedded into other systems to function as processing/controlling unit. In this project, we made use of ATMEG328, a three 16-bit Timer/Counters, 8K Bytes of In-System Reprogrammable Flash Memory microcontroller from ATMEL Corporation.

→Blood Pressure Formulation

The Blood Pressure measuring device makes use of the signals drawn from the CNY70 sensor. In this case, another sensor which will be positioned around the wrist is used. The circuitry is the same with that of the heart rate (both the finger and the wrist values of the sensors determines the blood pressure value). The blood pressure reading was estimated using the Heart Rate and the Pulse Transit Time obtained from the clock of the ATMEG-328. Using the millis () function, the microcontroller acts as a stopwatch. The millis () returns the value of time in milliseconds since the controller started. When the microcontroller starts receiving pulses from the wrist CNY70 sensor, the time of signal change is checked (from low to high and then from high to low) through a threshold value.

→The Display Stage- Liquid Crystal Display (LCD)

I made use of a 20x4 version of the LCD to show the digital values of the read heart beat rate, temperature and blood pressure simultaneously.

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#### →Sim900 GSM module This makes uses of its AT commands to send message about the health status of the user to the programed care giver’s number upon the press of a particular button in the design. Two of the terminals of the module (Transmitter and Receiver) was interfaced with the receiver and transmitter of the controller using serial communication. The GND terminal is also connected to the GND of the controller. The module requires a minimum of 4V 2A. But because the controller operates on a 5V 500mA which can’t power the module, a LM317 circuitry was designed to get the required 4V 2A as shown below: (

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→Construction

The construction stage involves the use of a printed circuit board designed on Express PCB software. The whole circuit was first simulated on Proteus before being converted to PCB.

All images shown below are my original works