#garfield Logs

May 24 2020

01:19 AM polprog: https://youtu.be/yGvYvIGKqss
01:44 AM rue_shop1: I'm looking for 2.000M now
01:46 AM rue_shop1: erm
01:46 AM rue_shop1: I hope thats not their cutting edge
01:48 AM polprog: Nah, but the student labs have so.e pretty old stuff
01:49 AM polprog: its mostly an old pc thats hooked up to a test setup, that does One Thing every time students do that lab
01:49 AM polprog: there are some different weird setups as well
01:49 AM polprog: like.. putting a dmm behind plexi so that the range cant be changed
01:50 AM polprog: heh
01:50 AM rue_shop1: my 1M resisotrs are between 20k and 50k off
01:50 AM polprog: Where do you even get Rs that precise?
01:51 AM rue_shop1: well, if you have a bag of 200 resistors, A FEW of them should be bang on
01:51 AM polprog: ah
01:51 AM polprog: but.. you surely have some 1% ones
01:55 AM rue_shop1: for some reason my meter has error thats unmistakably clock drift.
01:55 AM rue_shop1: nope
01:55 AM rue_shop1: not of all the values I need
02:11 AM rue_shop1: ok, and last 8M
02:12 AM rue_shop1: either by 6.8M+1.2M or 4.7M+3.3M
02:13 AM rue_shop1: I dont have 3.3
02:13 AM rue_shop1: and I dont have 6.8M
02:13 AM rue_shop1: hmm
02:14 AM rue_shop1: with the huge error on these, I might find 3.9's that work
02:17 AM rue_shop1: wait, some of these 3.9 are 3.3
02:38 AM rue_shop1: ok
02:38 AM rue_shop1: wow, I'm glad I didn't try to go with 10M range too
02:41 AM rue_shop1: ok, all my resistor cards are done then
03:48 AM rue_mohr: hmmm, not as much space in the 1U box as I thought
03:48 AM rue_mohr: still need to put a power supply in there
05:27 AM rue_mohr: the 10 ohm range might be more important than I was giving it credit for
05:27 AM rue_mohr: for the standard ranges, I can start E24 at 1k, but all the others need to start at 10k
05:29 AM rue_mohr: lots of the values I use bottom at about the 1k range
05:29 AM rue_mohr: hmmmmmm
05:31 AM rue_mohr: the issue is that the connection resistances are a large % of 10 ohms
06:31 AM rue_bed: I think 8 of the relays added up to 2 ohms, not completely sure yet
02:07 PM rue_mohr: pondering external memory chip for the resistor box
02:19 PM aandrew: rue_mohr: 50k on 1M is 5%
02:21 PM aandrew: generally speaking I find that if I'm starting to reach for REALLY high resistance Rs or really tiny capacitance Cs then there's likely a bigger issue in my circuit
02:25 PM rue_shop1: yea, I still see that as miles off
02:26 PM rue_shop1: I'm beggining to hate even 1% error
02:27 PM rue_shop1: well, it did make me realize that there are wide margins, and that I should make sure my circuits aren't too pickey about values (which happens if I'm too close to an operating edge)
02:27 PM rue_shop1: hmmm
02:27 PM rue_shop1: all the large memory chips are 3.3V or less
02:30 PM aandrew: why do you need large memory for a resistance box?
02:31 PM rue_shop1: lookup tables
02:31 PM rue_shop1: so, there is a thought
02:31 PM aandrew: lookup tables of what? I can't imagine needing more than a half kB?
02:31 PM rue_shop1: that if I mapped every resistance in the box better, I could have the controller apply whatever combo is required to get a more accurate value than the modules themselvs provide
02:32 PM aandrew: man dead HDDs ahve such nice bearings in them
02:32 PM aandrew: odd, but so nice
02:32 PM rue_shop1: which means every value from 100 ohms to 16M ohms in 100ohm steps
02:33 PM rue_shop1: BUT, I'm also having issues fitting the tables for E24-E192 values in the mega8
02:33 PM rue_shop1: thankfully, this does not have to be fast
02:33 PM aandrew: you could always use a parallel E(E)PROM with a 595 to shift the address/data out/in
02:33 PM rue_shop1: I was actually thinking of capping the relay update rate at like 4Hz to prevent wear
02:34 PM rue_shop1: maybe, I'm working out whats practical
02:34 PM rue_shop1: but I have some spare io pins, and I might as well atleast stick an eeprom/flash in there before I close the lid
02:35 PM rue_shop1: the level converters I have are 4 channel
02:35 PM rue_shop1: hmmmm
02:35 PM rue_shop1: I also have some 24x512
02:36 PM rue_shop1: haha I cant test my new firmware till I have the hardware re-assmbled
02:38 PM rue_shop1: arg I have to go shopping
03:14 PM Tom_L: wear a mask
04:10 PM rue_mohr: made it back alive
04:12 PM Tom_L: always good
04:17 PM rue_mohr: yea I need to assmble the resistor box to keep working on it
04:17 PM rue_mohr: really tired right now
07:53 PM Tom_L: https://www.youtube.com/watch?v=-oB6DN5dYWo
09:01 PM rue_shop1: the safety video?
09:02 PM rue_shop1: I'm sure thats the guy
09:02 PM Tom_L: using dd to backup the rpi sd
09:03 PM Tom_L: sure hope i did it right
09:04 PM rue_shop1: yea, been a long time since I seen this one
09:08 PM Tom_L: so how does dd work if you have 2 partitions?
09:08 PM Tom_L: and they show up as /dev/sdd1 /dev/sdd2
09:08 PM Tom_L: just access it as /dev/sdd/ ?
09:11 PM zhanx_ is now known as zhanx
09:12 PM rue_shop1: dd just copies data
09:14 PM rue_shop1: what do you want to do tom?
09:14 PM Tom_L: i'm doing it
09:14 PM Tom_L: back up the sd image on the sd to a file on the pc
09:15 PM Tom_L: sudo dd if=/dev/sdd of=~/rpi4.img
09:16 PM rue_shop1: hmm
09:16 PM rue_shop1: ok