#robotics Logs

Feb 15 2012

00:21 theBear heh, now think of a nice way to make the tacho work again and i'll be really impressed <grin>
00:30 rue_more mechanical or electronic?
00:30 rue_more (the signalling means to it)
00:31 rue_more cause its either a mechanical cable that turns, or its a electronic pickup
00:40 rue_more yup, using a 555 instead of 2 transistors and 8 resistors just saved a ton of space
01:50 theBear electronic, whether it's open collector or mechanical (unlikely in a pc fan) it'll be pwm'ing away, 7 volts higher than the 5v input it is supposed to feed
01:50 theBear maybe a little tiny opto
01:55 rue_more nope, reluctor
01:56 rue_more if you tear apart the cluster you will find a circuit board on the odometer that the signal goes to, on that you will find a resistor, zener and capacitor that form what looks like a shunt regulator, the capacitor will be pooched and the resistor will be burned open, replace the cap and I think the resistor is about 10 ohms, but its for overvoltage protection so the value dosn't seem to matter too much
01:56 rue_more theBear, :)
01:57 rue_more assuming its the same as what happened to my truck.
01:57 theBear erm, wtf are you talking about ?
01:57 theBear 40 and 80mm pc bldc fans
01:57 rue_more aaaah k
01:57 theBear and i still don't drive remember :)
01:58 rue_more in that case they take a signal off one of the phases
01:58 theBear yeah, the 'trick' is getting that signal out past the low side pwm back to the mobo now
01:58 rue_more do you have a speed controller on them?
01:58 rue_more yea
01:58 rue_more I was gonna say
01:58 theBear what do you think the fet was for ?
01:59 theBear why do you think i wanted p channel ?
01:59 theBear you crazy foo'
01:59 rue_more put a shunt resistor across the pwm circuit so that there is always a bit of current, see if that does the trick
01:59 rue_more you WANTED P channel?
01:59 theBear p channel can pullup like the pchannel i was replacing, therefore the tach works as intended
01:59 theBear lemme take a picture
02:00 rue_more its sub-500mA use a 2N3906
02:00 rue_more theres a good pnp that drives the gates of the fets you just pulled off
02:01 rue_more each fet gate is driven by a npn/pnp transistor set
02:02 theBear it's not sub 500ma
02:02 rue_more a muffin fan?
02:02 theBear erm, 4 fans, 2 big 80mm, a 40mm and a pci slot centrifugal
02:03 rue_more !time
02:03 tobbor My watch says its 00:00 Wed Feb 15 2012
02:03 rue_more I have to be in bed by 9"45
02:03 theBear you got ages left :)
02:03 theBear dammit, that was hard, you wait for this img to upload
02:04 rue_more hah pk
02:04 theBear hmmm.... how much drive you think i got pre fet ?
02:04 theBear current wise
02:05 theBear wtf is up with my speed ?
02:05 rue_more spikes, small,
02:05 theBear i think i might have a higain binned bd139 somewhere
02:06 theBear woah, ugly graphs on server bw, i think they throttled me for not paying the bill
02:07 theBear OH FFS !!!!! i give up, this imgur uploader app is stupid
02:07 theBear why can't i find the one i used to have ? just hit it, take picture on fone, magically uploads and shows me a link
02:07 theBear suffice to say, earlier i put a to220 mosfet in place of one less than 3mm wide
02:08 rue_more hmm
02:08 theBear ahh fuckit... i'll go without tachs for now, i'm tired of this
02:08 theBear i'll sort it later
02:09 theBear there's stuff in that computer i wanna get out/use, and i can't do that with it in pieces and scope leads and solder everywhere :)
02:10 theBear i wonder... 3904's with emitter? resistors, i am technically replacing a parallel pair of fets, sounds too hard this end of the day, it's hot now
02:17 rue_more not driven right then
02:17 rue_more cause its that or backlash, and those fans have no backlash
02:17 theBear what ? what's that or backlash ?
02:18 theBear the originals shorted cos i foolishly overloaded them without thinking about the consequences
02:18 theBear parallel d/s and 1k gate resistors on each originally, i just replaced a single one
02:18 rue_more must sleep
02:18 theBear i think so old buddy :)
09:09 rue_more the gate drive must not be strong enough
09:31 rue_more Tom_itx, got a funny one for ya
09:32 rue_more I forgot how to get eagle to show the power pins in the schematic
09:32 rue_more aha
09:32 rue_more found it
12:41 Tom_itx invoke
12:41 Tom_itx silly boy
16:20 Tom_itx http://www2.electronicproducts.com/UCLA_engineers_create_tandem_polymer_solar_cells_that_set_record_for_energy_conversion-article-newscn_14_feb2012-html.aspx
19:12 rue_more there are a bunch of breakthru's latley
19:15 rue_more so I need to work out if its ok to take and combine all the voltage dividers of all the current sennse amps
19:18 Tom_itx making some more u4 boards tonight
19:48 rue_shop2 cool
19:48 Tom_itx baking as we type
19:49 Tom_itx ones with the xtal like you have
19:49 Tom_itx i figured i'd use those boards up
22:05 Tom_itx rue_more
22:05 Tom_itx what program did i give you to blink the u4 led?
22:05 Tom_itx do you remember?
22:19 rue_shop2 no
22:19 rue_shop2 I dont know if I got source, I had to remake my own
22:19 rue_shop2 grr, it turns out I cant use any op-amp as a comparitor, I need 6 lm393
22:20 theBear yes you can, depending on output stuff you can use a diode and pullup/down or not, etc etc
22:20 theBear wtf you doing this week needing 6 of everything ?
22:21 rue_shop2 no, the output wont go low enough to reset the 555
22:21 rue_shop2 hexapod
22:22 rue_shop2 the min output voltage for tl072 tl083 lm1458 is all 2V
22:22 rue_shop2 the 393 goes right down to ground
22:22 rue_shop2 it would work if I put a pnp transistor on every one
22:22 rue_shop2 I dont want to
22:27 rue_shop2 well, their larger than I want, but I do have a lot of lm311
22:30 theBear what about diode and pulldown ?
22:31 rue_shop2 the lowest output voltage is 2V
22:31 rue_shop2 you cant make that go lower like that :)
22:31 rue_shop2 I already hurt my brain trying
22:34 theBear make it only pull up, resistor pull down
22:35 theBear diode series
22:40 rue_shop2 YAY!
22:41 rue_shop2 it looks like they use lm393 in most power supplies,
22:41 rue_shop2 it just happens I have abotu 50 pre-stripped power suppplies here for parts for the mecha
22:41 rue_shop2 SWEEEET!
22:41 rue_shop2 (computer power supplies)
22:57 Tom_itx ok, one is workng
22:59 Tom_itx i think two
23:09 rue_shop2 so, this is funny
23:10 rue_shop2 it looks like the makers of the ka7500 (tl494 knockoff) suggested in an example design to use the lm393 for soemting to do tiwth the fan
23:10 rue_shop2 and it was copied by a few other manufs thru modified application notes
23:10 rue_shop2 anyhow I ahve 10 lm393 so far and I'm not even thru the first box of supplies
23:10 rue_shop2 :)
23:11 Tom_itx well dammit, i screwed one of em up
23:12 Tom_itx at least 2 are blinking
23:23 rue_shop2 ok well, thats 12 of them, and I only had to go thru 45 power supplies
23:24 rue_shop2 didn't even have to dig into the large box of them
23:24 rue_shop2 :)
23:24 rue_shop2 looking at those power supllies, I have a LOT of optos
23:29 Tom_itx my paste mask isn't that good on this part
23:29 Tom_itx the pads are too wide for the qfn and give me grief
23:30 Tom_itx i may pull the 3rd one off tomorrow and try and fix it but it's shorted under the chip i think
23:30 Tom_itx or the chip is crap now