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.
Part in Eagle designed.