Teensy 4.1 GPIO input voltage concern

[hobbyist]

Hello everyone.

I'm working on a project involving a custom fabricated PCB that will interface with the Teensy 4.1 and various other sensors, including an Atlas Scientific EZO EC board. As I will be using a SD card on the Teensy for data logging, I have to use external voltage regulators to change my input voltage (5V USB) to 3.3V to power the sensors.

Here is my dilemma:

I'm using the NCP161 LDO regulator (Mouser product page: https://www.mouser.com/ProductDetail/863-NCP161ASN330T1G). After testing it today, I realized that instead of supplying 3.3V, it supplies around 3.7V.
As I will be using the EZO EC board (which communicates via Serial) with the Atlas Scientific Inline Voltage Isolator, I am concerned that the pullup resistors on RX/TX in the Voltage Isolator (https://files.atlas-scientific.com/basic-ezo-inline-voltage-isolator.pdf) will cause an input voltage of over 3.3V on the Teensy's pins.

Since this is outside of its operating parameters, I was wondering if I should use it in this state. I haven't tested it with the Teensy yet as I'm afraid of frying it.

Unfortunately, I can't change the voltage regulator, as I have already ordered (and received) the custom fabricated PCB.

Many thanks.

 

[liudr]

Hello,

The regulator should output 3.3V, not 3.7V. How are you measuring this output voltage? Do you have a decent multimeter?

 

[hobbyist]

Hello,

The regulator should output 3.3V, not 3.7V. How are you measuring this output voltage? Do you have a decent multimeter?

I'm measuring the output voltage by connecting the multimeter probes to the output and ground pins on the regulator. I think the multimeter is fairly accurate, as it read the USB voltage accurately when compared to a USB safety tester.

 

[aleglakov]

AFAIK Teensy 4.1 must be powered by VIN pin, which can handle 3.6...5.5V. So your stabilizer should be ok for powering Teensy thru VIN pin.

 

[liudr]

If everything is right, your regulator should output within specs but it's not. Touch your regulator with a finger tip. If it is warm, there' something wrong in your circuits. Unless you post enough information regarding your circuits, I suggest you follow aleglakov's recommendation and use teensy's VIN to feed power, then use teensy's 3.3V output for now to power your 3.3v electronics.