#avr Logs

Oct 04 2020

07:58 AM darsie: Can avrs run at 32 kHz?
08:07 AM cehteh: some (328p?) can also have 2 clock inputs and you can run one timer from a watch crystal and the mpu core by some faster one, or internal osc
08:08 AM cehteh: dedicated RTC's are usually better since they compensate temperature drift and crystal aging etc
08:11 AM darsie: I have a slave clock which needs alternating 24 V pulses every minute. When a small 10 V solar panel charged a small cap I want to boost it into a 24 V cap and when that's full, I want to pulse the clock. I thought an avr might be less complex than making this with comparators or so. But it shouldn't draw much power, as the solar panel is in the shade.
08:12 AM cehteh: doesnt need to be 100% exact?
08:12 AM darsie: Just for fun. Wouldn't display accurate time.
08:12 AM darsie: No. Would advance the clock whenever the big cap is full.
08:13 AM vmt: this just in; avrs have an MPU
08:13 AM cehteh: you can run an attiny from the internal watchdog oscillator at approx 128khz thats pretty low power and wont need an external crystal
08:13 AM cehteh: but also pretty inprecise
08:13 AM cehteh: and it could be that watch crystal is less power, read datasheet and figure out
08:13 AM darsie: I might need to check when the small cap is full, or just boost at a fixed frequency. Gotta see which is more efficient.
08:14 AM cehteh: attinys have comparators too
08:14 AM vmt: you can signal segfaults with an led \:D/
08:14 AM darsie: mhm. I guess they draw power, too.
08:14 AM cehteh: might be useful, they can be wakeup sources for interrupts
08:15 AM darsie: And I'd need a voltage divider, which would draw power, too.
08:15 AM cehteh: there are some tricks to disable that when powered down
08:16 AM darsie: thx
08:16 AM cehteh: when you add an rc filter/cap after the voltage divider you can also use pretty high resistance, but its going to be very slow
08:17 AM cehteh: haha .. i still have some LDR sensing thing open i want to try: http://tinyurl.com/y4zqvrux
08:17 AM darsie: Hmm, the avr needs its own voltage, too.
08:18 AM cehteh: there are ultra low quiecent linear regulators
08:18 AM cehteh: quiecent current
08:18 AM cehteh: since your AVR is likely only drawing a few mA that will work well
08:19 AM darsie: That might be too much.
08:19 AM cehteh: i mean when runnning not when idle
08:19 AM darsie: IIRC the panel had 300 uA.
08:19 AM cehteh: ah moement 32khz .. then much less
08:20 AM cehteh: yeah
08:20 AM darsie: Maybe fixed frequency boosting is the better compromise.
08:20 AM cehteh: well proper low power programming/design is a bit of a challenge ... like the voltage divider and so on
08:20 AM cehteh: nope
08:21 AM cehteh: linear regulators shine when you draw very low current
08:22 AM darsie: I mean running a boost converter cycle from the 10 V to 24 V at fixed intervals instead of measuring when the 10 V are full.
08:22 AM cehteh: in sleep mode they only need µA or less and when you draw 250µA then the loss would prolly be neglegible as well
08:22 AM darsie: Measuring the 10 V cap draws power.
08:22 AM darsie: fixed frequency is less efficient, but draws less power.
08:25 AM cehteh: https://www.microchip.com/design-centers/power-management/dc-dc-converters-regulators/linear-regulators-ldo/low-quiescent-current-ldo-regulators
08:25 AM cehteh: take a look
08:25 AM cehteh: owest Iq in the market: 20 nA typical
08:25 AM cehteh: etc
08:26 AM darsie: mhm. I'm not sure I want to get such specialized chips.
08:26 AM cehteh: i just seen that, i wonder if they are sourceable and affordable in small qunatities
08:27 AM cehteh: but thats as best as it can get, you find plenty slightly wors but still excellent ones
08:27 AM cehteh: https://www.st.com/en/power-management/low-iq-ldo-regulators.html
08:28 AM darsie: People are confused by the stopped clock. I wonder how it will be when its running irregularly :).
08:29 AM cehteh: i doubt you find any switcher thats can compete with that when you only draw 25µA
08:29 AM cehteh: i doubt you find any switcher thats can compete with that when you only draw 250µA
08:29 AM cehteh: datasheet ftw
08:29 AM darsie: Hmm, maybe I could put the two 5 V panels in paralell and don't need a converter for the avry.
08:29 AM darsie: avr*
08:31 AM cehteh: thats risky because solar panels can have pretty irregulat voltage depending on power draw and light intensity
08:31 AM darsie: I can use a protective zener.
08:31 AM darsie: and waste excess voltage.
08:31 AM cehteh: you can put a zener along to kill any excess voltage, but that wont really consewrve energy
08:31 AM darsie: :)
08:31 AM cehteh: also when you run the avr at very low frequency then its much better to run it at low voltage
08:32 AM darsie: mhm
08:32 AM cehteh: iirc it can go down to 1.8V or so at 32khz
08:32 AM cehteh: and then it shines saving energy
08:32 AM cehteh: no need to run at 5V that needs lots more current for no gain
08:34 AM darsie: A linear regulator still draws the operating current at 5 or 10 V.
08:34 AM darsie: I'd need a small buck.
08:34 AM darsie: But yeah, the current would be less at 1.8 V.
08:35 AM darsie: So maybe a 1.8 V regulator from 5 V
08:37 AM cehteh: maybe
08:37 AM darsie: The 24 V cap is 220 uF 35 V.
08:42 AM cehteh: btw you may also put the solat modules in series but tap the first one for the voltage of the avr
08:56 AM darsie: No, the same current must flow through all cells.
02:05 PM rue__ is now known as rue_mohr
11:43 PM day_ is now known as day