Community Digest

Top new questions this week:

What is the most efficient voltage divider for Arduino?

I need to make voltage divider, so I could read a battery voltage up to 14.4 V. Could I use very high resistance resistors for that, so the current would be very low (to not to discharge battery)? On ...

analogread voltage-divider  
asked by Name 4 votes
answered by Majenko 11 votes

Switching from one color to another

I'm using ws2812b 2x2 LEDs and have it switching between green and red, but only one of my LEDs on my 2x2 is lighting up. I'm using the "blink" FastLED sketch with Data pin 3 on my Arduino ...

arduino-uno ws2812  
asked by Darcy Billings 3 votes
answered by xbox gamer 4 votes

Measure audio frequency through pulse duration

Hello dear StackExchange users, i want to develop an Infrared blaster which i can plug into the headphone jack of a phone or console of choice. In order to communicate what frequency to modulate the ...

arduino-nano timers frequency  
asked by MyFairJulie 3 votes
answered by Edgar Bonet 6 votes

ST7789 TFT display only shows a correct image while Arduino reset button is held down - Why?

I am trying to get the ST7789 TFT display to work with Arduino. I followed online guides for connections and am using the fast library fron github and included workbench ino (

arduino-uno display tft  
asked by WildCat 2 votes
answered by WildCat 0 votes

USB-C as power input and analog audio out

I currently use USB-C to charge an arduino with a battery. I also use a headphone jack to output audio. I would like to combine those two and output the analog audio through USB-C (when it is not ...

usb esp32 audio  
asked by michi 2 votes

Hijack analogue doorbell chime to trigger nodemcu

I have an oldskool doorbell chime. What i would like to do is whenever there's a voltage flowing through the doorbell also trigger an HTTP call, which will trigger some smart home automations. I have ...

esp8266 nodemcu  
asked by Toby 2 votes

Why impedance between I/O pin and ground drops when Arduino is not powered

I have a 4KHz 5V pulsed signal connected to Arduino UNO pin2 (ISR). When the board is powered, the pulse is attached to ISR rising edge, and is working as intended. I don't know the output impedance ...

arduino-uno interrupt isr  
asked by 7E10FC9A 2 votes
answered by chrisl 3 votes

Greatest hits from previous weeks:

How can I get the source files for Arduino libraries?

I've been looking for a while inside Arduino's files to find the core library. However, I haven't found them yet. Where on my hard drive can I obtain the core library files (.cpp and .h) necessary for ...

library core-libraries  
asked by Anonymous Penguin 15 votes
answered by Ignacio Vazquez-Abrams 10 votes

Using millis() and micros() inside an interrupt routine

The documentation for attachInterrupt() says: ... millis() relies on interrupts to count, so it will never increment inside an ISR. Since delay() requires interrupts to work, it will not work if ...

interrupt timers millis  
asked by Petr Pudlák 13 votes
answered by Nick Gammon 16 votes

Difference between print() and println()

What is the difference between print( ) and println( )? I see none when I run a code.

asked by Phyman 100 7 votes
answered by Mathsman 100 5 votes

How to I make the Tx and Rx pins on an ESP-8266-01 into GPIO pins?

When programming an ESP-01 with Arduino IDE, how can I make the Tx and Rx into a generic I/O pins reliably? I think there's a command to swap the Tx and Tx with other pins. I tried serial.swap() but ...

esp8266 ide  
asked by vzxc 8 votes
answered by Isaias Munguia 14 votes

Getting BPM from the given code

I have found code that can blink an LED on Arduino according to Heart Beat. I am using AD8232 as a sensor for Heart Rate. Code for it is: // Variables int PulseSensorPurplePin = 0; // Pulse Sensor ...

arduino-uno sensors timers  
asked by Mudassir Hussain 2 votes
answered by VE7JRO 1 vote

Very long delay() possible?

I'm trying to make an opening and closing little door that should open or close every 12 hours. I was wondering if I could just make a small looping script with a delay() for 12 hours, delay(43 200 ...

arduino-uno timers  
asked by Fred Pannekoek 9 votes
answered by geometrikal 10 votes

"stray '/302' in program error" when compiling

For some weird reason, the following code doesn't compile. I get a "stray '\302' in program" error around volatile unsigned int encoderPos = 0;, and I have no idea what the issue is. I've been trying ...

programming arduino-ide sketch compilation-errors  
asked by user2950509 5 votes
answered by Ignacio Vazquez-Abrams 7 votes

Can you answer these questions?

Low power USB C power supply

I am searching for a tiny board to that accepts an usb-c cable and outputs 5v. To my understanding, for the few hundred milliamps two 5k1 resistors on the board would suffice. PD is not needed. I ...

power usb  
asked by Daniel D. 2 votes

SIM800C status LED not blinking

I am using an Allwin HW-537 SIM800C module. I am also using a 3.7V 2200mAH ICR18650-22F battery which discharges about 4-5 amps according to the datasheet. However, I am unable to get the status LED ...

arduino-uno gsm  
asked by user248817 1 vote

sro4m-2 waterproof ultrasonic sensor

I bought this waterproof ultrasonic sensor about 5 of them with the part number SR04M-2 Written on the PCB silkscreen Which is different from the usual SR04t-0.2, they are just not working, I don't ...

arduino-uno sensors ultrasonics  
asked by Jephtah Jephtah 1 vote
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