Hello everyone! I want to read in the tacho signal of two pwm-fans using the Arduino Nano 33 IoT. To have a proper digital signal, I am using pull up resistors. However, because I've got two tacho signals I think I need two pull up resistors. I've already read quite a lot about pull up resistors bu…

[image] seb_dev: The pull up resistors in the circuit are connected in parallel I beg to differ. They are connected together on the lefthand ends and go to 3V3, but the righthand ends go to different pins on the board so they are not in parallel. In any case , 1K resistors are far too low i…

Oh okay, than this is my mistake by assuming, that they are connected in parallel. Thanks for the enlightenment! I tried using the INPUT_PULLUP mode first, but I did get quite noisy results when trying to calculate the rpm values. Also, I couldn't find out if the Arduino Nano 33 IoT does have built…

Hi, [image] seb_dev: I couldn't find out if the Arduino Nano 33 IoT does have built in pullup resistors because I can't really read the schematics of it. You won't see pull_up in the schematic of the board as they are actually inside the controller IC. Thanks for producing clear circuit dia…

Ahh. Good to know. New thing learned. Thank you very much! :slight_smile:

With out a schematic It is hard to tell but so far it looks good. My preference is for external pull up resistors as the internal ones are not very stiff. The value of this internal pullup depends on the microcontroller used. On most AVR-based boards, the value is guaranteed to be between 20kΩ and 5…

All variables updated inside ISRs should be declared volatile to prevent them being put into registers by the compiler which makes them unavailable to be updated under some circumstances

Thanks for the tip! So this refers only on these variables, right? // define variables to calculate RPM unsigned long volatile lastTachoInterrupt_A = 0; // in ms unsigned long volatile tachoInterruptDuration_A = 0; // In ms unsigned long volatile rpm_A = 0; unsigned long volatile lastTachoI…

That looks right. Try it and see

Thanks, I will. Another thought has come to my mind. The Input-Pins of the Arduino Nano 33 IoT can only use 3.3V as Input-Voltage. "Connecting more than 3.3V on IO pins will damage the board." (source: GitHub - ostaquet/Arduino-Nano-33-IoT-Ultimate-Guide: Arduino Nano 33 IoT - Ultimate guide ). Als…

It would certainly seem to be a good idea not to feed the Nano 33 input pins with 5V. Personally I would use a level shifter like this one SparkFun Logic Level Converter - Bi-Directional or a simple resistor voltage divider

How to use pull up resistors to read two tacho signals individually?

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How to use pull up resistors to read two tacho signals individually?

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