Update: After approximately 6 years of use of this firmware, the off-time mode switching no longer works correctly. An off-time of even greater than 1 minute is interpreted as a momentary button press (off-time < 500ms). The flashlight can malfunction and behave like a "next mode memory" flashlight and can also unintentionally enter the hidden strobe mode. The nature of the decay of the bits in SRAM after the ATTiny is powered down has seemingly changed over time. As a result, I would consider this method of determining the off-time of the flashlight to be unreliable for long term use.
Flashlight driver firmware with ramping using off-time to switch modes on attiny13 nanjg drivers. #Modes The flashlight driver has 6 main modes: high, medium, low, moonlight, smooth ramp, ramp selection. (plus a hidden strobe mode).
To change modes the user must turn the flashlight off then on in less than about 500ms (off-time mode switching), such as by quickly pressing the switch halfway. The driver has optional mode memory, enabled if MODE_MEMORY is defined when compiled. The current mode the driver is in is memorized if in that mode for more than 1 second. The light will come on in the same mode the next time the light turns on.
#Ramping When the user goes in to ramping mode the light will smoothly increase and decrease brightness. A short press will select the current brightness and the light will stay at that level in ramp selection mode.
#Strobe To access the strobe the user must very quickly press the switch at least 3 times in a row, with very short on times in between.
#Off-time mode switching implementation Previously off-time mode switching was not possible without hardware modifications (such as adding a capacitor to a spare pin of the attiny). The method presented in this firmware can be used on a stock nanjg driver.
Off-time mode switching is implemented by storing a flag in an area of memory that does not get initialized. There is enough energy stored in the decoupling capacitor to power the SRAM and keep data during power off for about 500ms.
When the firmware starts a byte flag (decay) is checked. If the flashlight was off for less than ~500ms all bits will still be 0. If the flashlight was off longer than that some of the bits in SRAM will have decayed to 1. After the flag is checked it is reset to 0. Being off for less than ~500ms means the user half-pressed the switch (using it as a momentary button) and intended to switch modes.
This can be used to store any value in memory. Checking that no bits in the flag have decayed acts as a checksum on the flag and seems to be enough to be reasonably certain other SRAM data is still valid.
In order for this to work brown-out detection must be enabled by setting the correct fuse bits. I'm not sure why this is, maybe reduced current consumption due to the reset being held once the capacitor voltage drops below the threshold?
The smooth ramping mode uses the ram retention method described above. Without ram retention, the ramp selection would rely on the eeprom. The large number of writes required by the smooth ramp could cause the eeprom to fail if left on for an extended amount of time.
#Fuse bits Example of working fuse bit configuration avrdude arguments: -U lfuse:w:0x79:m -U hfuse:w:0xed:m