I've taken down 20 or so alarm panels, from the oldest electronic clock to the smart stuff with blue teeth, and what really turns me on is that ugly time switch module. A search of an alarm clock to make time switch principles, full-screen rc-charged formulas and 555 timer parameters, but you actually do it, you find that there are three things at the core that work: oscillating sources, counting comparisons, triggering circuits. To rationalize the three layers, the whole theory is clear. It's not that big。
What's the time switch principle for an alarm clock
The clock's time switch is a time comparator. There's a freely running counter inside the cmu that starts to go up, and the 6:30 you set is translated into a certain threshold -- when you count, you output a high-level pulse, which is the starting point of the entire switch。Thresholds are accurately converted from the rtc module according to the crystal frequencyWith a few ppm, the alarm clocks may ring early or late for a few seconds, but not in the summer and winter。
I used the 40khz crystal vibration programme early in the day, and it was easy to calculate, with one pull of battery voltage in the winter, frequency drifting, and time accuracy falling directly to minutes. Later on, the change was changed to 32. 768 khz, which was used to calibrate the contours of the chain, and the error was pressed within one second, which was the case。
How does a time switch work in an alarm clock
At that moment, the high level hit the locker, locking up the state of "time to ring." when the comparator returns to zero, the locker does not flip. It's called a lock, so the signal doesn't resonate once. Then the output is put on the beeper. I took off a double-bell alarm clock that used a dry clarinet as a mechanical triggerWhen the power is out, it's silent. It doesn't sound wrongAnd the benefits of this old structure are so real。
There's a wake-up window on the other side of the smart alarm clock, not just the tick at the whole point, 30 seconds in advance to the low volume, for a buffer period. The level of the code is to move the comparator threshold forward and add a gradual volume slope, which is slowly pushed up from almost deafness to less suddenness。
How do you select components for making an alarm switch
Do it yourself. Don't come up with stm32. Minimum cost formula: 32. 768 khz crystal vibrate, one cd 4060 decimal count, npn triode, eight trumpets, four things welded on a hole plate, one or 60 minutes。Cd 4060's inductively corresponds to different resistance valuesIt's a lot more intuitive than writing a code, and it's easy to measure with a watch on hand。
If you want to be on a single machine, attiny85 is enough. Six-legged, self-band comparators, hibernation electric currents are only a few hundred cents, one dollar at a time, and the pcb is smaller than the tablet。
With so many editions, i find the easiest to ignore is not how to "open," how to "stop." once the switch is off, it's completely disconnected and it's half-cycled to burn the horn. For the first time, the horn squeaked and the fuse broke and i'm still in the notebook。
