I'm building a simulate ECG circuit with this link: https://www.instructables.com/Digital-ECG-and-Heart-Rate-Monitor/
However, I make some changes for the supply voltage: I connect Vee to the ground, Vcc is 15V and I apply the the pulse wave with 1Hz frequency, bandwidth 500ms, Vpp is 10V. However, when I use the oscilloscope to measure the waveform of the output of the Instrumentation Amplifier (pin 6 of the 3rd LM741 from the top to the bottom), I got nothing but a straight waveform. However, in the multisim. the output generate signal waveform. Can someone help troubleshoot my circuit?
Here is my circuit:

 

Hi BC,
Welcome to AAC.
The VEE of -15V is essential for that circuit to work, setting VEE at 0V will give you that problem.
E

 

Why would you change the supply voltages and still think it would work?
You multisim simulation apparently did not use a good model for the 741 if it showed it operating with a single supply.
The ancient 741 cannot operate down to 0V with a single supply (look at its data sheet).
It is designed for ±15V supplies as Eric noted.

You could go to a single supply op amp such as the LM324, but the signal would need to be offset so it never goes below 0V.

 

Hi BC,
Welcome to AAC.
The VEE of -15V is essential for that circuit to work, setting VEE at 0V will give you that problem.
E

Can I supply Vee with +15V?

 

Hi,
No, you will destroy the 741's
What power supply are you using for the project.?
E

 

I'm using Anatek power supply

 

your schematics shows +/-5V while original shows +/-15V.
it is common for OpAmp circuts to use dial supply. this can still be powered from single 30V supply by creating virtual ground.

 

your schematics shows +/-5V while original shows +/-15V.
it is common for OpAmp circuts to use dial supply. this can still be powered from single 30V supply by creating virtual ground.
View attachment 289724

You mean create 30V then create a ground between the positive and the negative?

 

creat

your schematics shows +/-5V while original shows +/-15V.
it is common for OpAmp circuts to use dial supply. this can still be powered from single 30V supply by creating virtual ground.
View attachment 289724

Because from multisim, I saw it works and it has the nice waveform so I believed the actual circuit works also. I tried to make a -15V to supply Vee and when I connect to the Vee, the power supply drops voltage significantly and it sparks. I have separated -15V connection with GND already.

 

You mean create 30V then create a ground between the positive and the negative?

here is an example of virtual ground circuit.
it is just a pair of resistors and capacitors.

one side connects to large supply.
the other side is 3-terminal substitute for split power supply

 

here is an example of virtual ground circuit.
it is just a pair of resistors and capacitors.

one side connects to large supply.
the other side is 3-terminal substitute for split power supply

View attachment 289727

This is voltage divider with 2 equal resistors, right?

 

hi, BC,
Have you read this warning from that site.?
How do you plan to use this device.?
Moderation.

NOTICE: This is not a medical device. This is for educational purposes only using simulated signals. If using this circuit for real ECG measurements, please ensure the circuit and the circuit-to-instrument connections are utilizing battery power and other proper isolation techniques.

 

Why use the very old circuit you copied that has 55 years old 741 opamps and its patient is an antenna who picks up 50Hz or 60Hz from electricity in the air? The circuit has only one probe plus a ground to the patient instead of using two probes for a balanced heart signal plus a right leg connection that cancels any external interference.

The very old circuit uses a 60Hz notch filter to reduce the 60Hz electrical pick up. Guess what frequency is a normal resting heart beat? 60Hz.

An AD620 IC is a modern instrumentation amplifier that has a datasheet showing an ECG circuit with a balanced input and a connection to the patient's right leg to cancel interference.

 

Why use the very old circuit you copied that has 55 years old 741 opamps and its patient is an antenna who picks up 50Hz or 60Hz from electricity in the air? The circuit has only one probe plus a ground to the patient instead of using two probes for a balanced heart signal plus a right leg connection that cancels any external interference.

The very old circuit uses a 60Hz notch filter to reduce the 60Hz electrical pick up. Guess what frequency is a normal resting heart beat? 60Hz.

An AD620 IC is a modern instrumentation amplifier that has a datasheet showing an ECG circuit with a balanced input and a connection to the patient's right leg to cancel interference.

So what is the right solution for this?

 

hi, BC,
Have you read this warning from that site.?
How do you plan to use this device.?
Moderation.

NOTICE: This is not a medical device. This is for educational purposes only using simulated signals. If using this circuit for real ECG measurements, please ensure the circuit and the circuit-to-instrument connections are utilizing battery power and other proper isolation techniques.

It's a school project and I just designed for completion

 

Hi BC,
OK, I have moved the Thread to Homework Forum.

Mod.

 

This is voltage divider with 2 equal resistors, right?

So imagine this is the circuit
The breadboard on the right is to create 15V and -15V
Then I connect the negative voltage to the Vee

Hi BC,
OK, I have moved the Thread to Homework Forum.

Mod.

Where and what is homework forum

 

It is here, and it is for College or Homework Projects.

 

here is an example of virtual ground circuit.
it is just a pair of resistors and capacitors.

one side connects to large supply.
the other side is 3-terminal substitute for split power supply

View attachment 289727

@panic mode

 

Imagine this is the breadboard and the lab power supply with 3 terminal. The virtual ground that you mention is the ground of the entire circuit, right???