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MSP-EXP430F5438: Is it possible to read voltage values from the 3.5 mm jack?

Part Number: MSP-EXP430F5438

Hi,

Im currently working on a project were I have to read ECG values using a MSP-EXP430F5438. I have been provided with ECG electrodes which provides voltages through a 3.5 mm pin and now I am wondering how to read those voltages using the 12-bit ADC of the MSP430.  From the schematic provided below it seems that i could either connect one of the ADC channel pins to the 4.5 pin with a female to female wire and then select that ADC channel in software, or i could solder on two pins on the board in the holes that seem to be connected to the 3.5 jack (picture number 2) and connect those via wires instead. Im just wondering if my acessment seems correct as it doesnt seem like the 3.5 jack is connected to an adc channel like for example, the michrophone is. Has anyone had any experience of reading the 3.5 jack before?

  • Felix Ragnarsson said:
    From the schematic provided below it seems that i could either connect one of the ADC channel pins to the 4.5 pin with a female to female wire and then select that ADC channel in software,

    P4.5 is connected to R38, which is not populated according to the schematic. Thus, I'm not sure how connecting this pin to an ADC input will allow you to measure the ECG inputs. Even if R38 was populated, the ECG inputs would need to pass through the audio output amplifier, R14, C34, and finally R38.

    Felix Ragnarsson said:
    i could solder on two pins on the board in the holes that seem to be connected to the 3.5 jack (picture number 2) and connect those via wires instead. Im just wondering if my acessment seems correct as it doesnt seem like the 3.5 jack is connected to an adc channel like for example, the michrophone is.

    This sounds like a better idea. I'd suggest connecting the wire(s) to the ADC channel(s) that are exposed on headers, like P6.7, P7.4, P7.5, P7.6, P7.7. You may want to remove the passives around the headphone connector and the audio amplifier.

    By default, the MSP430F5438A uses Timer B to output a PWM to the audio amplifier which drives the headphone connector. As you correctly identified, this interface is not connected to an ADC input.

    Regards,

    James

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