About: Jim Lynch lives in Grand Island, New York normal ecg reading pdf is a software developer for Control Techniques, a subsidiary of Emerson Electric. He has two grown children, Liz and Chris. Jim lives alone with his dog Comet.
This instructable describes in detail the steps required to create an Arduino-based ECG simulator. This ECG signal is only a few millivolts in amplitude. The finished project is shown in the first photograph below. The project was built using an Adafruit Menta kit plus a few additional parts. The Menta kit includes a Arduino ATMega328P microprocessor with 32K of Flash memory and 2K of RAM memory plus an Altoids-type metal case which has enough room to fit a small numeric display, a potentiometer to adjust the heart rate, and three banana receptacles for the patient leads. The waveform was created by first doing a screen capture of a suitable waveform image from the Internet.
This picture file was then digitized using the open source Engauge program from Sourceforge. The resulting text file was further processed by a custom Python program that used linear interpolation to space the samples 1. 0 millisecond apart followed by formatting the digitized table into a C Language array construct that could be pasted into the Arduino sketch. To output an analog waveform on the Arduino Menta, an inexpensive Microchip 12-bit digital-to-analog converter was soldered to the Menta prototyping area. A signal to the required millivolt levels. The TI software that shipped with the Demonstration Kit was used to display the incoming ECG signal from the ECG simulator which agreed closely with the shape and amplitude of the ECG waveform captured from the Internet document.
While this project was directed solely at generating an ECG signal, the methodology could be used to create just about any waveform you can draw or extract from a document! The project also shows just how useful the Adafruit Menta kit can be when used as a starting point for a custom, one-off embedded micro-controller design. Twenty six years ago, I was in charge of of software development for the world’s first color heart monitor, the Mennen Medical Horizon 2000. The CRT display for this instrument was the first to make use of color for alarm conditions, alerts, and so forth. I wrote the software for the signal collection board and my astute and industrious office mate, Linda, wrote the software for the board supporting the menus and displays.
In a design feature rarely seen today, the 68000 boards communicated via a shared, arbitrated dual-port RAM memory. These ECG simulators can be bought on Ebay for a couple hundred dollars. As I near retirement, I’m interested in building a heart monitor for myself, you know all DIY and open source. These days you can get the entire analog front-end for an ECG monitor as an inexpensive integrated circuit from Texas Instruments. The ECG leads are wired through a 9-pin D-connector and a USB cable connects this board to the PC and TI supplies a sophisticated Windows application that lets you modify all the chip’s control registers, view the signals, and so forth. The first step in learning about any sophisticated chip is to get a data sheet and an evaluation board.
TI evaluation board there must be an ECG signal. Why not just hook yourself up with some ECG leads and those conductive pads they use in hospitals? First, Texas Instruments would totally freak out since there are no protection circuits on this evaluation board. By this I mean the isolation circuitry, the Zener diodes, the neon-lamps, current-limiting resistors normally used to protect the patient are not present on this board. Obviously I could buy a used ECG simulator, but that wouldn’t be any fun. How about building one from scratch? I looked at possible solution platforms and a nice starting point is Adafruit’s Menta kit.
ATMega328P 8-bit microprocessor with 32k of Flash memory and 2k of RAM. Notice that Lady Ada designed it to fit into a metal Altoids-style case. Looking at the Menta and applying a little arm chair engineering, we’ll need to fit three banana receptacles on the top to attach the three ECG leads, a pot with a knob to adjust the heart rate, and a small 4-digit 7-segment numeric display to show the dialed-in heart rate. A converter down to a couple of millivolts, which is the amplitude of a human ECG signal detected via chest electrodes. The Menta can be powered via a cheap 9-volt Wall Wart using the power connector on the left.
00 Adafruit Menta is a kit that you must assemble. In the spirit of and even better than Heathkit, Adafruit has a detailed tutorial on their web site that shows how to assemble the Menta. In my case, it took less than an hour to solder the kit together. A chip, which communicates via the SPI interface. SPI 8-bit transmissions to send the 12 bits plus four configuration bits. A converter will operate at a rate of 1000 updates per second, or in other words 1.
A signal will be updated as part of an on-board Timer2 interrupt handler. I’m sure that this device would be also perfect for this application. The pin layout for the MCP4921 is given below. For the 4 digit heart rate display, I considered three possible solutions.