In the developing world, engineers do not have adequate resources to properly repair medical equipment. The development of a low cost electrocardiogram (ECG) tester would greatly enhance an engineer's ability to debug problems in current ECG machines. This project seeks to create a low cost alternative to current ECG simulators that, despite its low cost, is compatible with the interface of different ECG machines.
Because of the poor economic situation and lack of medical resources in the developing world, this device must cost less than $4 in quantities of 500, achieve minimal maintenance and considerable longevity. Specifically, this device must output a normal sinus rhythm waveform including the P wave, QRS complex and T wave at varying heart rates as well as a 1 mVpp sine wave in order to test the function and the frequency response of the ECG machine. The target heart rates for the device are 40, 70, 130, 190 bpm and the target sine frequencies are 1, 5, 10 and 50 Hz. The main goals of this project are to create a safe, reliable, low cost device which can simulate the normal sinus rhythm of the heart. Addition of the sine wave output and varying pulse rates would improve the product and are desired, but will be completed if time and resources permit. Through the development of this device, engineers will have a more effective way to identify problems with ECG machines and subsequently test repairs made to malfunctioning ECG machines.
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Step 1: Specifications
- Output various waveforms
- Sine Waves
- 1 mVpp4 @ 1 Hz, 5Hz, 10Hz, 50Hz
- Normal Sinus Rhythm Waveform
- Include P wave, QRS complex, T Wave
- 40, 70, 130, 210 bpm5
- Mimic the impedance of the chest cavity at device outputs.
- Cost less than $4 in quantities of 500.
- Blink an LED that corresponds to the frequency or rate of device when it is on.
- Achieve minimal maintenance and considerable longevity.
- Maintain functionality for 10 years.
- Switch contacts
- No encapsulation will be used because of the complexity of the switch.
- Last for at least 1 year on 3 AA batteries, assuming a sporadic 20 hrs per year of usage.
- Measures less than 4" x 4" x 1" when stored.
- Three alligator clips on the test will clip to the positive (right arm), negative (left arm) and ground (left leg) leads of the ECG machine.
Step 2: Materials
1 Battery Pack
3 Alligator Clips
1 330K Ohm Resistor
3 560 Ohm Resistor
1 33 uF Capacitor
Small Phillips Screwdriver
Step 3: PCB Layout
Step 4: Install the 330k Ohm Resistor
Be sure to save the lead from the resistor, as it is reused as a jumper.
Step 5: Jumper Wire
Use the lead from the 330K resistor.
Step 6: Install the 560 Ohm Resistors
Step 7: Insall the LED and Capacitor
Make sure to install the LED with the longer of the two leads facing towards the left.
Step 8: Install the Alligator Clips
Step 9: Install the PIC
Make sure that the semi-circle indicating the top of the chip is facing the left when installed in the PCB. Also, be careful not to put too much solder on and short two pins together.
Step 10: Install the Battery Pack
Note, while the battery pack is located on the back of the device, its actually soldered on the PCB the front of the device.
Step 11: Drip Solder on the PCB Pads
This is done to increase the longevity of the device, be sure not to get the pads too hot, or the PCB may be damaged.
Step 12: Testing the Device
If the batteries are installed the LED will light up. If a clip is used to short any one of the 8 pads, the LED should blink.