Ecg Heart Rate Monitor Design

keane2097 · 2009-02-19T05:08:22+00:00

I'm currently building a heart rate monitor based on the MSP430 from Texas Instruments. This is the schematic I'm basing my preamplifier design on, it's a TI design with some electrical isolation added: I've built a test version of the circuit on breadboard and I want to check that I've done it properly without attaching it to myself... Unfortunately I'm not sure what input signals I should apply to test it suitably. Basically, can anyone tell me what kind of signal I should apply to the right-leg driven circuitry and to each of the inputs that will be connected to the patient's arms? Thanks

Ecg Heart Rate Monitor Design

keane2097
@keane2097-lj8VzD

Updated: Oct 26, 2024

Views: 1.2K

I'm currently building a heart rate monitor based on the MSP430 from Texas Instruments. This is the schematic I'm basing my preamplifier design on, it's a TI design with some electrical isolation added:

I've built a test version of the circuit on breadboard and I want to check that I've done it properly without attaching it to myself...

Unfortunately I'm not sure what input signals I should apply to test it suitably.

Basically, can anyone tell me what kind of signal I should apply to the right-leg driven circuitry and to each of the inputs that will be connected to the patient's arms?

Thanks

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keane2097

Member • Feb 19, 2009

Could somebody possibly explain this section of the schematic to me specifically please?

I can't really understand what it's telling me to do here with regards to the connection of + and - Vcc, seemingly to the Vin+/- pins?

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keane2097

Member • Feb 23, 2009

So I've gotten the circuit in the schematic built on breadboard and I'm now happy enough that all the connections are correct.

I'm having a problem with the supply voltages though.

I'm using a power supply to generate a +5 to -5 voltage. The +5 is being used to provide the instrumentation amplifier with its positive supply. I'm then using two voltage dividers from the +5 and -5 signals to get the 2.5V supplies for the OPA2335 op-amps.

Unfortunately when I connect the op amps to the voltage divider the voltage drops considerably and the amps aren't therefore supplied with the desired +/-2.5V.

I've tried buffering the two signals with voltage followers. Again the output from the voltage followers are the desired +/-2.5V but when I connect to the op-amps the voltage drops again and I don't get the supply I want.

Clearly I'm absolutely hopeless with analog circuitry. Can someone please give me an idea of how I can drive the desired voltages into my op-amps so i can get back to the land of 1s and 0s asap!?

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Kaustubh Katdare

Administrator • Feb 23, 2009

Guys, no response here? I'm sure lot of electronics engineers are reading this thread!

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keane2097

Member • Feb 23, 2009

The_Big_K
Guys, no response here? I'm sure lot of electronics engineers are reading this thread!
I hope it's ok if I keep replying with my progress in the hope that somebody joins in at some point if they can help? Anyways...

I think part of the problem was that I was trying to supply the op-amps with a duel supply of +/- 2.5V as I didn't really understand the function of the pedestal reference voltage.

The setup i now have is as follows:

I've got pin 7 (positive supply pin) of the Instrumentation amp connected to pin 8 (positive supply pins) of all the op amps. These pins are all connected to a 5V supply.

Next I've connected pin 4 (negative supply pin) of the Instrumentation amp connected to pin 4 (negative supply pins) of the op amps and these pins are all connected to 0V from the same power supply.

Finally I have two 10k resistors connected in series between 0V and 5V. I'm taking the centre point of the two resistors (2.5V) to supply the non-inverting inputs of the 3 op amps A2, A3 and A4 with the 2.5V pedestal voltage.

Does this all sound ok?

When I turn on the power supply to the circuit when set up like this I'm immediately seeing the voltage drawn drop to almost nothing, and the power supply is telling me I have a short circuit somewhere.

Does anything in my power supply setup give a clue as to why this might be or have I simply got something wrong somewhere else in the circuit building?

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sauravgoswami

Member • Feb 23, 2009

well buddy,your power supply is loading,so use separate batteries and see as for input signal,well please check the frequency of heart-rate set that frequency in the generator and check how it responces,sorry for the delay man,but do share your queries!!!

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keane2097

Member • Feb 23, 2009

sauravgoswami
well buddy,your power supply is loading,so use separate batteries and see as for input signal,well please check the frequency of heart-rate set that frequency in the generator and check how it responces,sorry for the delay man,but do share your queries!!!
Thanks for the reply.

So you think the frequency of the input signal is more important than the amplitude when I test the circuit correct?

Incidentally, I figured out why I was getting the short circuit I mentioned in my last post - I tested the op amps by making a little voltage follower and one of them was blown. I replaced it and the short circuit disappeared.

I've now gotten rid of the voltage divider and I'm using a separate power supply to give me the 2.5V pedestal voltage. I've also added a voltage regulator at the input to stabilise the 5V supply...

I'll keep ye posted on my progress...

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sauravgoswami

Member • Feb 24, 2009

well thats true,as heart beat are in pulses,please google to see wat are the rate of pulse and amplitude as well!!!

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keane2097

Member • Feb 24, 2009

sauravgoswami
well thats true,as heart beat are in pulses,please google to see wat are the rate of pulse and amplitude as well!!!
Yeah I've been trying to use a 5Hz frequency square wave of amplitude 10mV as input to the left arm input line.

I've been tying the right arm input to the right leg input after being advised to do so elsewhere. I'm unclear as to whether I should nevertheless be feeding an input into the right arm input line.

Any idea?

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keane2097

Member • Mar 2, 2009

I've been testing out various parts of the circuit on their own since I still don't have the overall circuit performing correctly...

I've been having a look at the integrator part of the circuit and I've built it stand-alone to test it. This is the setup I have:

Now all the theory I've come across suggests this should behave as a low-pass filter, and indeed this is the behavior I see when I test the circuit, however in the overall schematic of the ECG Amplifier it seems to be suggested that it should behave as a high-pass filter to eliminate baseline wander...

Can someone please explain how the setups differ?

Thanks...

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keane2097

Member • Mar 6, 2009

I'm currently trying to debug my circuit by building the different blocks separately and making sure they are working as expected. Currently I'm looking at the O/P amplifier as shown:

The setup I'm using is supplying the op amp with +/- 2.5V and I've got the positive input grounded. The negative input takes in the signal...

If I have, say, a 10mV p-p sine wave as my input what should my output be? I'm guessing I should be getting a 2V p-p sine wave from the schematic, but I'm not sure how to do the calculations to confirm this?

Thanks

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keane2097

Member • Mar 12, 2009

Ok, so I have the entire circuit working now (thank god). I'm getting an ECG signal out of roughly 1V amplitude which is what I was looking for. All I need now is a quick method of isolating the patient from the power supply for safety.

Is there a quick, easy way to do this? Like with diodes/capacitors maybe?

I'm using a dual supply of +/- ~5v

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