Looking at the SX1509 documentation, and its companion SX1509 class object, I find a number of parameters that clearly interact with each other. I am specifically speaking about the interaction between sleepTime and scanTime.
It is clear to me that scanTime determines how often the key-down interrupt signal will occur. Near as I can tell, with sleepTime=off, an interrupt pulse will occur every (scanTime*rows) milli-seconds. Therefore, this sets the maximum number of key-presses that can be detected per second.
From the name of the parameter, I would expect that sleepTime has something to do with allowing the hardware to “sleep” in order to save power.
Questions that come to mind are:
What effect does sleepTime have on key-down response time?
Does sleepTime have any effect on non-keypad SX1509 functions that may also be in use?
Yes; longer sleep times increase the maximum potential delay between a key press and its detection, up to a max of: sleepTime + (scanTime * rows)
SleepTime primarily affects the keypad engine and has limited impact on other SX1509 functions:
GPIO : SleepTime does not directly affect GPIO operations. The SX1509 can still handle interrupts and I/O changes while the keypad engine is in sleep mode
LED driver functions: The LED driver operates independently of the keypad engine. Functions like PWM, blinking, and breathing should continue to work regardless of the keypad’s sleep state
Power consumption: Enabling sleepTime can significantly reduce power consumption for the entire chip, which may be beneficial for battery-powered applications or when using other low-power features of the SX1509
I2C communication: The SX1509 remains responsive to I2C commands even when the keypad engine is in sleep mode, allowing for configuration changes or data reading/writing
Add’l Tips:
Use the lowest sleepTime setting for responsive applications
Increase sleepTime only when power conservation is a critical priority
Always validate the actual performance in your specific use case through empirical testing