Questions tagged [rtc]

Questions regarding Real Time Clocks (RTCs) which can be a timekeeper IC used by microcontrollers, or using a microcontroller as an accurate timekeeper. Some have calendar, alarm, interrupt or heartbeat features, while some simply keep track of time since last programmed (Epoch timers are similar).

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Combined timer/RTCC [closed]

I have been using a Maxim DS3231 as a RTCC with its alarms used to "wake up" certain hardware. Now I need to wake up the hardware periodically, say every hour, so I actually need a timer (...
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MAX 32660 Schematic Questions

I do have some questions regarding the MAX32660 MCU from MAXIM. See the documentation: User Guide Datasheet 1. RTC-Pins: For routing purposes I would like to connect the 32KIN/OUT ports to GND. I do ...
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5 votes
2 answers
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Symbol identification (J?)

I am looking into a part from a application guide titled How to Calculate UNIX ® Time Using a PIC18 Microcontroller and the MCP795W20 SPI RTCC. And there is a part that I'm not sure what it's suppose ...
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Do I need RTC while I'm using NTP?

We know computer and another device like microcontroller is not accurate in ticking clock comparing to wall clock that using cesium atom. I heard RTC module is purpose to making accurate the ticking. ...
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1 answer
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RISC-V GD32VF103 battery backup domain

I'm not sure how the VBAT pin of the GD32VF103 RISC-V MCU should be connected, exactly. The GD32VF103 User Manual states: The Backup domain is powered by the VDD or the battery power source (VBAT) ...
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4 votes
1 answer
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Can a memory backup supercap hold on for more than 2 weeks?

Most RTC chips have a VBATT input for backup power supply; besides a battery, you can use a supercap there, e.g. using the following scheme: simulate this circuit – Schematic created using ...
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Are There Any Standards for RTCs, Similar to JC42 Temp Sensors?

When I place a temperature sensor on a board, I like to use a JC42-compliant temperature sensor. I know of at least half a dozen manufacturers that build these temperature sensors in exactly the same ...
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LiPo cell as RTC backup battery

I am wondering what is the sensible way of using the LiPo cell that powers a handheld device to also act as the RTC backup battery for the MCU. There is charging circuitry for the LiPo cell on-board ...
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Simple circuit to sample 120 VAC and yield 8.33 ms pulses

Have you noticed the lack of availability and prices of RTC chips lately? A simple DS1307 RTC is simply not available right now. Last year I purchased DS1307s for less than a buck. Now they are $4+ ...
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USB not working when internal 32kHz RC is enabled

Controller is XMEGA128A3U. I have been using the USB for several years without issues. To implement some additional features for the product, I wanted to use the internal RTC peripheral. Using the RTC ...
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DS3231SN RTC -- timing between 1Hz SQW and clock seconds?

I don't think this is addressed in the DS3231SN datasheet but I may be missing something. When the SQW output is programmed to output a 1Hz signal, is there a known / fixed phase relationship between ...
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I2C bus slave powered before raspberry pi master

I have a number of I2C slaves (PCF85063AT) connected a Raspberry Pi, which acts as master. For various reasons the I2C slaves are powered at all times, where the power to the Pi can be controlled on/...
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I2C via MCU works with FLAG_WRITE_READ but not FLAG_READ

I'm reading the date from an RTC via I2C using a SiLabs MCU. There are two different flag options, but only the 2nd one works. I'm new to implementing I2C, what is happening on the wire that works ...
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Converting code with Boolean to a byte array

I am having a hard time understanding this code. I have code I am working on to sequentially flash the current 12 hr time on a single 7-seg display when you press a button. I used a Boolean matrix to ...
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1 vote
1 answer
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DS3231 Question

Can someone help me understand the differences between: "Adafruit DS3231 Precision RTC Breakout" and one of these generic breakout modules, "DS3231 AT24C32 IIC RTC Module"? Why I ...
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0 votes
2 answers
110 views

Arduino + DS3231 Wristwatch Help

I am a mechanical guy looking to expand my electronics skills. I would like to make a simple digital watch mainly for academic fun. Right now I am running into endless issues due to my inexperience. ...
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1 vote
1 answer
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sniffing a 32.768kHz low-power oscillator

I'm troubleshooting a real-time clock and suspect that under certain conditions the oscillator stops. How could I check if it is running, especially when the RTC chip is on battery power? It is Maxim ...
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Pull-up resistors needed between DS3231 and AHT10?

I'm trying to create a datalogger using DS3231, AHT10, ESP-01 and MicroSD Module. So far I noticed that the AHT10 is returning wrong fixed readings: -50 for temperature and 0 for humidity. When tested ...
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Can a low side L-spike destroy a turned off microcontroller through its ground pin?

I am working on a low power project involving servo motors and an STM32 Bluepill MCU board and I was wondering if it was necessary to place a free-wheeling diode as shown in the schematic below (D1). ...
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Coin battery for powering the RTC while MCU power down: is safe for ATEX ZONE 2 or DIV2 in hazardous environment? The Box is heavy duty IP67 sealed

I wish to use RTC which keep powered by a coin battery (i.e. CR1225) while disconnected from +5V power. The box is heavy aluminum diecast with IP67 sealed. I was concerned about using coin batteries (...
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Is it possible to use the RTC alarm signal on the tamper pin in order to hold that value in a D flip flop? STM32 (bluepill)

I've been doing a lot of research concerning Low power modes for the STM32 (Bluepill) and I was wondering if I could power my board through VDD and then, right after going into sleep mode, I would use ...
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2 answers
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Diode OR with more than two sources

Is this type of system a good idea? I tried multiplexing two coin cells, one USB and one booster using four Schottky diodes (CUS10S30.) Schematic is given below. The RTC does not work properly in this ...
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3 votes
2 answers
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Looking for an extremely low power RTC module (and more!)

I'm working on a project called The Fifty Year Beep. The goal is to produce a battery-powered circuit that will beep once and only once fifty years from now. It is an art project of a kind, inspired ...
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2 answers
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32 kHz crystal freezing problem [closed]

I am using a 32 kHz crystal for RTC in STM32F030R8 for time and date. It is freezing all time and when I touch it with my finger, it starts working. What is the problem? Unfortunately I do not have ...
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How can MOSFET drain be used as ground for a load?

I'm trying to understand how the schematic from this github repo works. It uses an RTC to turn on an arduino, via a npn transistor and a mosfet. I'm novice with electronics, so this might be a ...
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1 answer
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How to set time for an RTC 5 Click in MPLAB X?

I am currently working as a design engineer intern. I am using an RTC 5 Click as part of my design to provide real solar time. It is nice that MPLAB X is able to generate sample code, but I have no ...
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RTC with ATmega 32 & ds1307 showing the year completely wrong

I have this project to build a clock / calendar with ATmega and ds1307 showing it on a 20*4 LCD (LM044L). I have implemented the code showing the time correctly, i have initialized the RTC too, but ...
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1 vote
0 answers
257 views

Bit-bang I2C implement on DS1307 and Atmega328P problem

I currently implement I2C bit-bang for Master Arduino (AVR) to Read/Write to Arduino Slave using Wire.h and DS1307 RTC. My bit-bang i2c work perfectly with Arduino Slave read 8 bytes without ...
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What's wrong with this cable?

I have a circuit with an RTC (DS1307) and an LCD display, both connected to an I2C bus. Because the RTC requires a 5V level (the RTC breakout I use has built-in pullups) I also use a level shifter. ...
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1 answer
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How does the RTC of a STM32L0 keep the time accurately when using the LSI as the clock source?

I am working on an application that must keep track of time (using a RTC), and will be uploaded on a STM32L052K8. When I was making my hardware I just assumed that I will use the low speed internal (...
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1 vote
1 answer
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MAX32660 rev A2 subsecond count

How do I access the subsecond counter (1/256 second) on the MAX32660 rev A2? I tried reading MXC_RTC->ssec, when busy=0 and ready=1, as suggested in Chapter 9 of ...
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3 votes
4 answers
202 views

Why is NMI commonly pulled high on many ARM SoC schematics?

I've noticed that "AP-NMI" is pulled high on several ARM SoC schematics, and it is pulled high by the real-time clock (RTC) voltage, which is an always-on power domain (battery backup). Why ...
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Raspberry PI 4 Compute Wakeup Circuits

on the raspberry PI 3 computer IO boards datasheet it has on page 10 (first sheet) is has the option to connect jumper 13-14 to wake up the computer module by connecting global_en to run_pg run_pg is ...
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0 votes
1 answer
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Abracon AB1805 RTC IC - additional resistance on VBAT pin?

I intend to use Abracon AB1805 RTC in designed device, powered by a CR2032 battery. IC datasheet contains a note: * Total battery series impedance = 1.5k ohms, which may require an external resistor ...
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2 answers
50 views

Low Temperatures Effect on RTC module

How would low temperatures effect the following RTC module? I'm talking around -20 degrees Celsius. It can be seen on the picture that it uses the DS1307N version, which is industrial (-40 to 80 ...
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RTC Calibration - ppm Offset to Adjust Clock Rate Faster/Slower, by How Much?

I have a TI MSP432P401R board. I have looked through the various other questions related to RTC calibration and I have not found an answer to this seemingly simple question. The MSP432 SDK driverlib ...
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1 vote
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218 views

ESP8266 using DS3231 to wake up from deep sleep

I am using the Arduino IDE to program the ESP8266 and am able to set the time, alarms on the DS3231 and test to see that they are firing. My problem is that I would like to use the SQW output to wake ...
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Error Real Time Clock implementation AVR microcontroller

I want to create a real-time clock using ATmega328p microcontroller. The microcontroller's frequency is 1 MHz. So, I think I should use timer interrupts in CTC mode to generate interrupt every second. ...
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0 votes
4 answers
139 views

Crystal tolerances and what that means for timer interrupts

I'm developing a system that needs to periodically wake up and perform a process. We're currently targeting for an hourly wake up (give or take, this spec is very loose). The key here is the unit cost ...
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1 vote
1 answer
99 views

Interfacing DS1302 - is the schematic I found correct?

On the following website there is a project of a 7-segment clock, which uses DS1302 as RTC. The DS1302 is connected to the microcontroller in the way that I don't really understand. Can someone please ...
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External clock input for Atmel SAMD21

Is it possible to use a 32.768kHz square wave, such as the output from the DS3231 RTC, as an input for something like the SAMD21 microcontroller? I would rather not have to add a crystal to my design ...
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1 vote
2 answers
157 views

RTC circuit supercapacitor charge/discharge doubts

This is my current RTC circuit... Supercapacitor = DXJ-5R5V334U (ELNA)... DXJ-5R5V334U = 0.33F, 5.5V, ESR = 150 Ohms Resistor = 150 ohms 0603 100mW 1% If I consider only the resistor, I have a RC ...
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1 vote
1 answer
75 views

How do I give several classes access to the single RTC on my MCU

I'm writing my first large-ish C++ embedded program on a STM32F413. I've become a reasonably firm believer in object oriented coding but am not particularly knowledgeable. The STM32F413 has one RTC ...
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2 votes
1 answer
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Replacing Dallas NVRAM with larger capacity variant?

This DS1225AB-200 (8k x 8 = 64kB NVSRAM) is from 1995 and is probably dead (cannot measure from the outside.) The only close replacement in stock is a DS1230AB-100 (32k x 8 = 256kB.) Looking at the ...
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Properly isolating I2C for powered off MCU

What is the proper way to isolate the I2C lines of two devices where one is powered on and the other can be powered down? I'm not 100% sure if isolation is even necessary, but I suspect it is. Here is ...
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Nano Power Soft Latch

I need to latch an INT output with a time width of 7 ms. This signal is generated by an RTC clock and I need to enable an LDO with it. The LDO powers an MCU, which at the end of its program should be ...
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3 votes
2 answers
157 views

Suspected PIC alarm bug with RTCC module in PIC16LF series, cannot set alarm to 00 seconds

This question is about understanding the functionality of RTCC alarm registers within one PIC family. While I am using 16LF19176, I believe this question relates to all RTCC modules in this family. I ...
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1 vote
1 answer
725 views

How to switch ON a Raspberry Pi, Arduino, ESP32, etc from SQW pin of RTC DS3231

My issue is how to build the circuit and what is the most efficient one to trigger a MCU from the alarm of the RTC DS3231. For the momment I have built the one in the picture below (using a P-channel ...
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0 votes
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475 views

RTC time is not kept in Stm32f103 by vbat

I am using stm32f103c8 and External Clock Crystal (LSE). I connected the Vbat with a 1220 coin battery. But when I turn off VDD and turn on the micro again, the time and date are all zero. Why time is ...
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212 views

Why do most microcontrollers not embed a 32k oscillator?

Why do most embedded systems use an external 32k oscillator?
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