This is my first post here, so please forgive me if I'm supposed to be posting this elsewhere.
Over the passed couple of months I have been working on an indoor gardening project that has been a fun learning experience, however I have ran into a situation where my lack of knowledge is beginning to show it's consequences.
I am using a DS1307 RTC as a source for an alarm function in order to turn on and off relays and LEDS, so far so good. My problem is that I need a way to revert to the last known state of LEDS and relays controlling lights and fans in case of a power cut.
There will be 2 main alarms for the lighting, Alarm 1 to turn on the lighting at given time, Alarm 2 to switch it off. In case of a power cut I need to revert to the last known state of the light and not have to wait for the next known alarm function.
I have read that I can save the last known state to the EEPROM but that will quickly become a problem especially if I need to save every minute or so, can an SD card module be used or an ESP32 ?
I am not expecting anyone to write the code for me, but any sketches or helpful information concerning the code and hardware would be highly appreciated.
Over the passed couple of months I have been working on an indoor gardening project
Indoor gardening sounds like something that is illegal where I live...
I am using a DS1307 RTC as a source for an alarm function in order to turn on and off relays and LEDS, so far so good. My problem is that I need a way to revert to the last known state of LEDS and relays controlling lights and fans in case of a power cut.
The DS1307 has 56 bytes of battery backed RAM. Should be plenty of storage space for what you need.
I use EEPROM in exactly the way you want.
The trick is only to write when you ‘need’ to.... (to save write cycles)
I run all the values in RAM until power fails or the unit is shut down.
Then I write to EEPROM, and read the values back when the board restarts.
In many sites this may be ,o this, weeks or at least a couple of days between (restarts) writes.
There are several posts about this on the forum, dig around. a diode, electrolytic capacitor and three resistors on an analog input pin for you to monitor the raw supply voltage. Voila. A 470uF capacitor gives me enough time to save >2K of data when the supply fails.
I run all the values in RAM until power fails or the unit is shut down.
Then I write to EEPROM, and read the values back when the board restarts.
In many sites this may be ,o this, weeks or at least a couple of days between (restarts) writes.
This concept doesn't work if you have power failures (not a controlled shut down) because in that case you don't have the power to write anything to the EEPROM.
Power-fail save to EEPROM works fine... as I said with a complete power loss (pull the power lead), I have time to save > 2K to EEPROM with a 470uF electrolytic & voltage divider before the regulators)
I have more than a hundred units in the field using this hardware & code every day (in rural applicrions with flakey power and randy cows that rip out customer's cable etc !
Here's a demo board running on my desk...
> (HERE IS WHERE THE POWER INPUT IS SIMPLY PULLED FROM THE BOARD)
(POLLing the ADC input in loop() sees the input voltage has gone below a threshold)
EEPROM SAVED (The magic happens here)
------------------------
*** CYCLE POWER TO *** (Information only on the console port)
*** RESTART SYSTEM ***
------------------------
(This is just part of the normal 'crash stop' sequence )
Modem power-off... (irrelevant if power is already gone!)
Build: Jan 14 2020
------------------------ (### RESTORE POWER CABLE HERE ###)
EEPROM 0x7, 2827b (Reade power-up states here (2.8 KB of EEPROM data)
PASSCODE is BLANK
------------------------ (This is a battery backed 3G cellular project...)
Modem power-on, init, Registered
SIM: READY
WCDMA 850 Telstra Mobile
Use carrier time (no RTC needed here - DST also handled autromatically !)
Modem is awake
00:00 Out 1 ON (These two relay outputs were re-instated from a LAST-KNOWN status )
00:00 Out 3 ON
========================
ControlMate v200112 (Firmware version announcement
------------------------
Sold To [factory] (SIte/customer info - from EEPROM)
SITE: Default Site
Panel Mode:100 (LCD enabled)
Using Last known ( <<--- User selectable in the configuration )
SIM5320-A (info for support)
IMEI: 01xxxxxxxxxx071
PASSCODE []
========================
System Ready
CLK: Wed 200115 08:38 (cell time has been set INTO the controller)
Hmm, ok if you don’t have a shield or breadboard.
OP was asking for a solution to add to his DS1307 RTC based project. My UNOs don’t have an RTC or I2C pull-ups either.
OP was asking for a solution to add to his DS1307 RTC based project. My UNOs don't have an RTC or I2C pull-ups either.
A voltage divider before the regulator isn't that easy even if have a breadboard. If OP powers it's setup by USB for example.
And the code must be very responsive as your capacitor powers the Arduino 20ms under ideal conditions.
All I wanted to say: It's not a solution valid for everyone. It seems to work for you but fails in a lot of situations.
