Hi everyone,

I am currently working on building an ECG simulator based on a reference design I found online.

Here's the link to the project: https://mauriciopagano.wixsite.com/ecgprojectsimulator

The question is: I want to simulate the circuit in LTSpice prior to building it. However, it is not very clear to me what should the input for Pin 14 be.

According to the datasheet of the CD4046 and HEF4046 it should be a digital input. Would I need to use a 555 timer to generate such signal?

From my understanding, it seems the input to pin 14 is an external input through the header pin attached to the PCB.

The layout and schematic are available below.

I would appreciate any clarification on this matter.

Thank you for reading.

Giovanne Lucas Barreto

 

hi gio,
Please post your LTSpice asc file.
E

 

Hi Eric,

I am attaching two files. The 002 is the one I need help with.

The 001 one is another circuit I simulated. But it is limited as it does not output RA, LA and LL. Just an ECG form wave.

I am planning on building 002 to test my ECG reader.

Thank you for the reply.

 

According to the CD4046 datasheet, pin-14 input is 180mV AC coupled, 360mV max @ VDD = 5V.

 

A 55 years old 741 opamp does nothing with a supply that is only 5V. Almost all its specs are with a 30V supply (+/-15V).

 

Hi MrChips, I checked the datasheet and added a 180mV AC senoid to pin 14 and tried to simulate it.

However, I don´t know why but my computer is taking about 2-3 hours to simulate the circuit.
Plus, the wave form was not correct. I have seen that before, it might something about the OpAmp gain.

Hi Audioguru again, yes I know they are quite old. Instead should use something like an OPA333 right?

I am attaching the updated asc file here.

 

I do not know if the simulator software knows that an old 741 opamp has no output when its supply is only 5V or 9V.
The OPA333 opamp has a maximum allowed supply of only 5.5V, it is very slow and its maximum output current is so low that it might not be able to drive your low resistances.

 

The datasheet says pin 14 on the 4046 is self-biased. Instead of adding a biased input, just connect a 100nF cap between your input source and pin 14, just like Mr Pagano did with C10 on his PC board.