Very LOW Power Arduino - Precise Time Interval Wakeup! using an RTC 

Hey, Kevin! I have a small project here, where I used only an ATmega328P (and a crystal) to create a RTC internally on it. If anyone is interested, here's the code and schematics: github.com/jdneto/Atmel-Projects/tree/master/ATmega368p-168pa-88pa-48pa/timer2-as-rtc-with-leds. The average current at 3.3V is about 8uA.

There is possible to combine two alarms (ALM0 and ALM1) to cooperate. Then you can wake up Arduino for example on specific Hour and Minute or specific Hour of any Day of the week. See 5.5.2.2 Dual Alarm Operation and TAB5-10: DUAL ALARM OUTPUT TRUTH TABLE

Hi Kevin, At 1:17, you suggest "Why not use the internal watch dog..", and you list that you're limited to turning on every 12 second and then going back to sleep. I agree with you that the RTC clock is more accurate, but as far as I can tell, the while loop you have set up has the same problem. It turns on every 12 seconds, checks to see if the alarm flag is triggered and then goes back to sleep. Accuracy is better, but POWER USAGE is basically the same as far as I can tell? Am I missing something? Another option, instead of using the interrupt, is to simply use a RTC Date Time library, and then RtcDateTime now = Rtc.GetDateTime(); RtcDateTime alarmTime = now + 1000; // 1000 seconds into the future or however long you want. while(alarmTime > Rtc.GetDateTime() ) { SleepFor12Seconds(); } This should do the same thing without needing the interrupt pin. The downside is that all these methods you are still limited to wakeup within 12 seconds of the alarm and not exactly on time.

I've designed a simple board with ATmega328p's internal rtc with external 32.768kHz crystal directely connected at TOSC1(PB6) & TOSC2(PB7) pins. It draws abot 1.1uA (vcc 3.3v) in power save mode with accurate time keeping! Also you can use the internal rtc interrupt to wakeup the processor in any time. I'm running the cpu at 1.8432Mhz with calibrated internal oscillator via OSCCAL by the help of internal rtc. So it's easy and I can run the UART at 115200 with the minimal external hardware, only one 32.768kHz crystal!

I can't find an MCP7940 module online, just the chip itself. Can I achieve the same result with a DS3231?

Nice video, gives me more insights. I use the 328p sleepmodes with watchdog. I understand the difference with and without using the watchdog is around 6uA (using 6.5uA with and 300nA without, I am not able to measure this tiny current myself). Looking at the datasheet of the MCP7940 shows it uses 1uA. So if I want to save 5 uA, I just need to add the RTC module.

Great tutorial! A channel well worth subscribing to.

Nice Kevin

Brilliant ! Well done- informative Video. Will use these with my Afterschool Arduino program. and just subscribed- Thank You !

Very cool! Keep it up!

You've made a latch circuit once. Perhaps use the RTC to turn it on and Arduino to turn it off? That will kill Arduino and save you some power?

If I ran this basic blinking setup out of 2xAA 1,5v batteries how much time would it last? And hiw mich time would they last if the arduino was awake without RTC doing the same work instead if sleeping?

Thank you, you answered my quetions

great. thank you.

Awesome video! Where do I pick up the board to solder the parts into? Do I have to have PCB's made or can they be purchased somewhere? If I have to have them made, is there a file for that? I saw a wiki picture of the layout but didn't see a place to download it. Thanks again!

That's really awesome work! One question though, the checkAlarm function could just return the result of the condition, couldn't it? Instead of the if statement with a return 1; and return 0; in it, a return ((alarm0Check >> 3) & 0x01) == 1; should suffice. It's returning a boolean after all. Heck, I think even return (alarm0Check >> 3) & 0x01; would do just fine as & 0x01 can only result in 1 or 0, which will be interpreted as boolean true or false.

Will you do a video on how to use an ESP8266-12 on the lowest possible power consumption for keeping the WiFi connection On. Using an RTC of course. I read, it can wake up and ready to send in under 2ms!

Hi Kevin, may I ask two questions? In your circuit, both the RTC board and the Arduino board are powered off of the VCC rail on the breadboard and the current in sleep is only 1.5uA. Or is the RTC running off its own battery? Asking because the RTC datasheet says ~ 1.2uA @ 3.3V for time keeping + the Arduino which I would have expected in the 3-4 uA range. And secondly, looking at this 328P board - is there any good reason why one would go even further and only use an ATTINYxx instead? For even lower low power consumption? Thanks so much!

Excellent info again Kevin! This is probably a dumb comment, but why not use 'C' type commenting /**/ ? I think I know why you comment rather than #if's though as I have many options in my code and it's hard to see what's happening (especially with multiple nested #if's).

goToSleep(0x10) does not mean 16 seconds ?

By removing a couple of resistors and clipping the vcc leg you can reduce the current on $1 DS3231 modules from 100uA down to 5uA which will give you alarms for >4 years on the backup coincell. This power saving modification is quite useful for our battery powered data logging application: thecavepearlproject.org/2014/05/21/using-a-cheap-3-ds3231-rtc-at24c32-eeprom-from-ebay/

Where to find this 328 board for sale? Cant find any info about it and its not on eBay or Ali.(

Hey! I want to be an embedded systems engineer when I graduate. Should I be working with the Arduino IDE for hobby projects or should I use something like the MSP430 and code it the hard way?

All well and good ... if the user is a programmer. But how does one take input from a non-programmer then set the alarm to the date, year, month, day, hour, minute and second?

Can you make a vedio about 32786MHZ with timer2 ?

What about using a cmos 555 timer ?

Kevin, is there a way for an RTC's alarm to switch a mosfet and turn on an arduino?

How long can you run an RTC that sends an interrupt every 15 mins just of the coincel?

make a low power 8mhz arduino video!

What Arduino board are you using in this video?

how do I change the mask to boot up every 7 days instead of every 10 seconds?

Witch arduino is this?

Whats up with your arduino?