I would like to present my project which I made four years ago. It was wireless electrocardiograph which work with mobile device.
Main presumptions of project:
- simple analog front-end working with ARM device and responsible for data collection and transferring,
- mobile device with android system as receiver which was responsible of data presentation,
- Bluetooth connection via BTM-222 module.
As device responsible for data collection and pre-processing I had choose STM32F0Discovery board with custom ECG module
Analog front-end had simple instrumentation amplifier with low-pass amplifier as second stage. Additionally it contained also boost-converter which was responsible to provide 5V supply for board from 3,3V battery. Here is schematic of ECG amplifier:
At input we have high-pass filter with cutoff frequency set to 0.15 Hz it is instrumentation amplifier with gain set to 13 Second stage it is non-inverting amplifier with gain set to 69 This amplifier is also low-pass filter with cutoff frequency set to 106 Hz This analog-front end have band 0.16 Hz 106 Hz and total gain equal to 59 dB Here is photo of this ECG amplifier
This board contains also BTM-222 Bluetooth module and it was connected to STM32F0Discovery board Here is photo where this board is connected to STM32F0Disocvery
STM32F0Discovery was responsible for following things
- conversion of ECG signal from analog-front end to digital data,
- digital processing of data: averaging, normalization, digital filtering (50 Hz notch filter and down-pass filter),
- connection and transferring data to mobile device.
Program was written in C language. Here is diagram with flow of application:
Mobile device with Android system was responsible for receiving and data presentation. Application was written for Android in version 2.3.5 and used graphic library called: achartengine. Here were responsibilities of mobile application:
manage connection to STM32F0Discovery board via Bluetooth
- presentation of received data: (ECG wave and heart rate variability),
- data collection to file.
Here is example screen-shoot of application:
In attachments there are source code for both applications. It was really nice project where I learned a lot of about analog and digital electronic.