duty cycle
Say I have a uC active for 1s every 100s, sleep otherwise. This will lead to 1% duty cycle.
But what if it is active ones every ten seconds, and once every 100 seconds, and then once every week? Over what period of time do I calculate the duty cycle?
Your assumptions are basically correct. 100 mA for 10 uS, then off for 15 uS would provide for a 40 mA average and not exceed the specs.
It's always good to "derate" your stuff. A 1/4 watt resistor would normally not carry more than 1/8th watt in normal operation, and your 40 mA diode would carry maybe 20-30 mA on average. There is no hard and fast rule to derating components, it's all a balance of cost, lifespan, availability of parts, PCB area, etc. In the end, it is usually just a guess by the engineer.
Resistors are often derated 50% on power, electrlytic caps are derated 30-50% on voltage, CPU's are almost never derated on clock frequency. Diodes are derated in the neighborhood of 25-50% on power or voltage. Of course, if this is a one-off project where failure isn't terrible then don't derate at all! :)
See the image:
Frequency = \$\dfrac{1}{T_{cycle}}\$ and Hertz is the unit of frequency. It gives the number of cycles in one second.
Duty cycle = \$\dfrac{T_{high}}{T_{cycle}}\$. It gives fraction of one cycle for which the signal is high.
Best Answer
If I read your question correctly then you have a wakeup at three different intervals simultaneously:
In this case you have to calculate the duty cycle over the longest interval, in this case one week. Then calculate all the smaller intervals in terms of the larger one.
A week is 7 days, each day is 24 hours, each hour has 3600 seconds, so your week is 7*24*3600 = 604800 seconds. During this interval you will wake up:
In other words, in 604800 seconds you will wake up 60480+6048+1 = 66529 times. Calculate the wake time for each wakeup (in seconds, even if it is fractional), multiply it by 66529 and divide 604800, then multiply by 100%: this is your duty cycle.
Duty cycle = \$\dfrac{66529 * seconds_{awake}}{604800}*100\%\$