For keeping the time for the Cat Feeder Unreminder I am planning on using the LTC2956-1 which is a super low power timer that has push button reset control. It can accurately handle very long timers that a traditional RC style timers (think 555 timer) wouldn’t be able to do.
For my use case, I am going to pull ONMAX to GND which will disable the timer that turns off the AWAKE timer. I will toggle the Sleep pin from low to high to low to reset the timer.
To handle the timing aspect of the Cat Feeder Unreminder I am going to use the Analog (It is actually a Linear Technology part!) LTC2956 timer component.
This is a wake up timer IC that has built in push button support for reset. Perfect for this project.
The timer itself is configured with just a few resistors and can range from 250ms to 39 days. Setting it to the required 22 hours is a piece of cake for this timer.
In shutdown, it only pulls 800nA while active and 300nA in shutdown mode which is one of the lowest current use for a timer that I can find.
To set this up for the Cat Feeder Unreminder we need to stay in RUN MODE. The device can’t leave SHUTDOWN MODE without interacting with the PB switch and that would make for a hungry cat. The AWAKE STATE with EN=1 is when the device will tell us to feed the cat. SLEEP STATE with EN=0 is in standby counting till next feeding
ONMAX to GND
This sets the T ONMAX time to the max
T ONMAX will stay FALSE
We don’t want the device to auto fall into the SLEEP STATE
SLEEP to a switch
We will use this to send the device to the Sleep State
Active Lowq
Set LONG to max time
Tie PB HIGH
Makes sure we don’t fall into SHUTDOWN MODE
Set Period/Range for timer to activate in 22hrs
This should allow the EN pin to go high every 22 hours and will reset low when the push button on PB is pressed.
