voltage splitter to avoid 5V input to teensy 4.1

[kteepa]

Hi,

I am using a bunch of different sensors (FSRs, photodiodes) with the Teensy 4.1. I am adding this EEG shield to the same teensy: https://www.mikroe.com/eeg-click

Unfortunately, the EEG Click (above) is supposed to be used with a 5V development board. I know that if I hook it up normally (teensy 3.3V to the EEG Click, and teensy ground to the EEG Click, with EEG click output to the teensy analog port), any additional electrical input through the EEG electrodes (such as the EEG signal) will cause the voltage that goes into the teensy analog port to be above 3.3V, which is bad.

So instead, I have hooked up the power and ground from the teensy to the EEG click normally, but I have tried to implement a voltage splitter between the EEG Click output and the teensy analog port. I connected EEG Click output to a 10 Ohm resistor, and then I connected that 10 Ohm resistor to a 10 kiloOhm resistor to Teensy's ground. I clipped between those two resistors and that is where I am connecting Teensy's analog port. The Teensy will *always* be plugged into the computer, which is plugged into a wall power outlet, during use with the EEG Click.

I have three questions on the resulting circuit:

1) In this setup, is the EEG Click drawing more than 3.3V from the teensy?

2) Am I actually successfully preventing more than 3.3V from being fed into the Teensy pins?

3) Is this method going to somehow disrupt teensy's ground and thereby affect the teensy or the other sensors/their readings?

Thank you for any insight!

 

[mborgerson]

If the EEClick can output a signal of up to 5V, then your combination of 10-Ohm and 10KOhm resistors won't protect the Teensy. It only reduces the input voltage by one part in one thousand.

To get the protection you want, your first resistor should be at least 6K Ohms. With that in place, the T4.1 input will be 10/16 of the EEClick output, or about 3.1Volts.

 

[kteepa]

If the EEClick can output a signal of up to 5V, then your combination of 10-Ohm and 10KOhm resistors won't protect the Teensy. It only reduces the input voltage by one part in one thousand.

To get the protection you want, your first resistor should be at least 6K Ohms. With that in place, the T4.1 input will be 10/16 of the EEClick output, or about 3.1Volts.

Hi, thanks for your reply. So if I use 6kOhm which then connects to the 10kOhm that goes to ground, that is fine? Does this prevent more than 3.1V from leaving the EEG Click at all, or does it cause the same amount of voltage to be split except now more of the current goes into the teensy ground instead of the teensy analog pin?