I am designing a circuit board for a flashlight and I need to put a delay on the battery voltage to a voltage divider. The background is that I use a capacitor which is charged when the light is operational, and read the capacitor value when turning the light on. This is to determine weather power off was a quick power off to change modes of the flashlight, or if it was off for longer (no mode change). I also need to monitor the voltage level from the battery so it is not discharged to deeply (Li-ion cell). Previously I have had the "off time" capacitor and the voltage divider on separate pins to the MCU. No problem, works fine. On startup the pin that the capacitor is on is set to input, I read the value with analog to digital converter, then I set the pin to output high to charge the capacitor for the rest of the power cycle.
Now I want to do this on the same pin (all other pins on the ATtiny85 are used for other things). When I turn on the power I would like to delay the voltage that goes to the voltage divider with about 150ms to 300ms, and then keep feeding the voltage to the divider after the delay. This is because I have the "off time" capacitor on the same pin and would like to read the voltage level of the capacitor before the battery voltage feeds the voltage divider, which will charge the capacitor. I have extremely limited space and need to do this with as few and as small components I can find. What would the best solution be?
By searching I found a Microprocessor Reset Circuit that I thought I could use, it's the ADM1818 from Analog Devices. It's small (SC-70) and appears to have a delay of about 150ms before sending out high on reset. My problem is here that I can't figure out if the high that comes out on the ADM1818's reset pin after the delay is a pulse or if it stays on constantly high while the flashlight is on. I need it to stay on as the ATtiny85 will be used to monitor voltage level of the battery after reading the capacitor. Will it work? If it does work, will the output on the ADM1818 basically be the same as VCC (with voltage drop)?
I've been searching and searching, but as a total beginner I don't know what terms to use when searching. I don't know what delay devices that I'm looking for are called. I don't know how best to solve this. I looked at delay lines, but the delays on the ones I found are far to short.
Now I want to do this on the same pin (all other pins on the ATtiny85 are used for other things). When I turn on the power I would like to delay the voltage that goes to the voltage divider with about 150ms to 300ms, and then keep feeding the voltage to the divider after the delay. This is because I have the "off time" capacitor on the same pin and would like to read the voltage level of the capacitor before the battery voltage feeds the voltage divider, which will charge the capacitor. I have extremely limited space and need to do this with as few and as small components I can find. What would the best solution be?
By searching I found a Microprocessor Reset Circuit that I thought I could use, it's the ADM1818 from Analog Devices. It's small (SC-70) and appears to have a delay of about 150ms before sending out high on reset. My problem is here that I can't figure out if the high that comes out on the ADM1818's reset pin after the delay is a pulse or if it stays on constantly high while the flashlight is on. I need it to stay on as the ATtiny85 will be used to monitor voltage level of the battery after reading the capacitor. Will it work? If it does work, will the output on the ADM1818 basically be the same as VCC (with voltage drop)?
I've been searching and searching, but as a total beginner I don't know what terms to use when searching. I don't know what delay devices that I'm looking for are called. I don't know how best to solve this. I looked at delay lines, but the delays on the ones I found are far to short.