#avr Logs

Feb 01 2019

05:20 AM janco__ is now known as janco
05:35 AM LeoNerd: cehteh: Hrm.. I'm not really sure about that,... unsure if I've ever really powered it that way with USB still connected.
06:01 AM [1]MrMobius is now known as MrMobius
08:41 AM cehteh: LeoNerd: ugh .. i dont know the usb specs if it requires diodes on the usb side guess not, that could become ugly
08:47 AM * cehteh puts a schottky in
09:25 AM LeoNerd: cehteh: diodes where..? On the D+ / D- lines? I think the CH340 chip includes them
09:25 AM cehteh: LeoNerd: from my vreg to the mcu
09:27 AM cehteh: then when externally powered the mcu runs at 5V- shottky drop, when powered over usb then usb power is on the mcu but wont creep into the vreg
09:27 AM LeoNerd: Oh, into the 7805? I don't think that minds
09:28 AM LeoNerd: I run mine like that (USB-powered) all the time
09:28 AM cehteh: would be better when you add 2 (ideal) diodes to your pcb or at least find some way that one could cut traced and add that externally
09:28 AM cehteh: i have an external recom
09:30 AM cehteh: they dont like reverse power the datasheet says, and even if not, the recom is exactly 5V and 500mA rated, when i plug it into a USB i dont wnt it ro power the usb bus just because the computer only supplies 4.95V
09:31 AM cehteh: aka 2 diodes would be better, but the later one cant be added as is, dunno what happens now when one powers the computer where it is connected down
09:31 AM LeoNerd: I'm not following your suggestion now
09:32 AM cehteh: https://www.arduino.cc/en/uploads/Main/Arduino_Nano-Rev3.2-SCH.pdf
09:32 AM cehteh: look at the '+5V AUTO SELECTOR"
09:32 AM cehteh: the rpi has some true ideal diode to switch between inputs
09:33 AM LeoNerd: Huh. interesting that they keep the FT chip on the +5V side of that and not VUSB
09:33 AM cehteh: prolly doesnt matter
09:34 AM cehteh: or actually you want to have the ft powered even when no usb is connected not to generate spurious signals/resets
09:34 AM LeoNerd: So, this is stopping power being supplied -into- the USB connector when the board is self-powered..? I'm not sure why you'd do that
09:35 AM cehteh: 2 cases: a) VUSB is slightly below your own external power
09:35 AM cehteh: then you regulator tries to lift the VUSB to its reference
09:36 AM cehteh: which may end up regulators fighting each other, alt least your vreg will power the usb bus then
09:36 AM cehteh: b) computer is powered off (but some loads are still connected to the usb bus via hub or else)
09:37 AM cehteh: then your vreg tried to power up the whole usb system :D
09:37 AM LeoNerd: Hmmmm
09:37 AM LeoNerd: I guess I could add that
09:38 AM cehteh: i mean i understand thats not you necessarly need to put on your board, but some pads/pins/traces to adapt would be nice
09:38 AM cehteh: or at very least put a shottky on the VUSB .. better a ideal diode, but that adds some costs and takes space
09:39 AM cehteh: btw sid you seen my cursing from last weekend the 328pb have some issues improper doc or even bug on the silicone
09:40 AM cehteh: worked around that, but i shit bricks when the timer didnt PWM when it should
09:40 AM cehteh: https://www.avrfreaks.net/forum/atmega328pb-timer-34-output-compare-pwm-issue
09:40 AM LeoNerd: Ooh, I haven't seen that no
09:41 AM cehteh: dunno if thats a odd behavioir which got wrongly documented or more likely an actual silicone bug
09:41 AM cehteh: and if thats fixed on newer batches
09:42 AM cehteh: nowhere mentioned in the datasheet errata
09:48 AM cehteh: https://www.analog.com/en/products/ltc4420.html .. no way you could add such one or?
09:49 AM cehteh: why arent there any simpler ones, 4 pins
09:49 AM cehteh: well maybe some simple 2 way schottky would be 'good enough'
09:50 AM cehteh: aka sot3 should be feasible to add
09:51 AM LeoNerd: Two diodes, or maybe two FETs might suffice
09:52 AM cehteh: fet isnt as trivial
09:53 AM cehteh: iirc you need some gate driver
09:53 AM cehteh: https://www.analog.com/en/products/ltc4357.html
09:54 AM cehteh: there are controllers for that .. but that one isnt applicable
09:55 AM cehteh: moment iirc the rpi has something integrated
09:58 AM cehteh: https://www.digikey.com/product-detail/en/richtek-usa-inc/RT9741CGV/RT9741CGV-ND/7066425
09:58 AM cehteh: https://www.zeanoit.de/pdf/9c-RT9741DGV.pdf
10:22 AM vmt: rpi - so you can run linux to control some discrete fets
10:23 AM vmt: it's so 21st century!
10:23 AM vmt: not withstanding the fact that i didn't bother to read the whole discussion
10:29 AM vmt: better yet, you can run nodejs so you can have a restful api to control your discrete fets
10:39 AM cehteh: vmt: yes you totall missed the discussion
01:57 PM I_M_Mohr: It IS a bot, nobody say anything!
01:59 PM I_M_Mohr: one down, wait for that other one...
02:01 PM I_M_Mohr: ack, this ones a bot too!, I'll get it, I almost have this otherone, everyone just keep quiet, don't feed them...
04:07 PM vmt: i_m_mohr == rue?
08:59 PM [1]MrMobius is now known as MrMobius
10:44 PM davor_ is now known as davor
11:39 PM day_ is now known as day