Why in schematic - operation amplifier is - TL074?

[Ildaron]

looks like some misprint

[lorforlinux]

It's not a misprint, TL074H/TL084H can be used.

[sarkrui]

Hi @lorforlinux i am considering to remake one using smaller SMD packaging OpAmp chips. Would you recommend ADA4691-4ACPZ-R7 for example? plus, would anything wrong (any disadvantages) if the system power supply is 3.3v, i am thinking to use nRF52 chips as the MCU. Thank you!

[AdamM68]

nrf52 :)
waiting for !

[lorforlinux]

@sarkrui Yes, that amplifier looks like a good choice. make sure nrf52 ADC can handle full 0v - 3.3v analog input, esp32 can only record 2.1v/2.5v/3.1v depending on the type of esp32 you are using, and for that type of ADC, you have to update the reference power supply voltage divider circuit to create Ref voltage = (ADC max voltage readable) / 2. I think it would be better if you create another issue if you have any other questions.

@AdamM68 We have created a new board with 3ch EXG input capability, we have tested it for ECG, EMG, EOG, and EEG. It works very well for all biopotential signals. If you are interested in getting pre-release units for your projects you can email us at contact [at] upsidedownlabs.tech