#robotics Logs

Sep 11 2014

00:12 rue_mohr2 heh, its intersting watching ebay play with the session expiry timer
00:13 rue_mohr2 wow, and the fluctuations in the canadian dollar
00:45 rue_mohr2 #@$%@^&@#%$@#$%^ the LM317 regulator datasheets do NOT say what the dropout voltage is
00:45 mrdata hrm
00:46 rue_mohr2 so, if I have a 10V led, and I want 300mA, so there is a 4.2R resistor for the 1.25V feedback, running off a "12V" SLA battery, ...
00:46 rue_mohr2 what voltage does the led start getting dimmer?
00:47 rue_mohr2 (lm317 as current regulator)
00:47 rue_mohr2 I dont think a 12V battery is enough
00:47 rue_mohr2 damn I hate the overheads on analog solutions
00:48 mrdata um, fig.10 dropout voltage? http://www.onsemi.com/pub_link/Collateral/LM317-D.PDF
00:49 rue_mohr2 flipping -5V supplies just to get op-amps to 0V
00:49 rue_mohr2 (thanks)
00:49 mrdata Vin - Vout ~ 2.0V maybe?
00:49 rue_mohr2 so I'm about 1.75V
00:49 rue_mohr2 less 1.25V for the current sense
00:50 rue_mohr2 10V for the led
00:50 rue_mohr2 so I need atleast 13V to get 10V to the LED
00:50 mrdata yep
00:50 rue_mohr2 I'm better off with a resistor
00:50 rue_mohr2 kinda
00:51 rue_mohr2 somewhere between 7 and 12 ohms
00:51 rue_mohr2 :/
00:51 rue_mohr2 wait, i can do this with a bipolar...
00:51 rue_mohr2 WHY DO i RUSH OUT AND BUY THE PART FROM EBAY BEFORE TESTING THE IDEA PROPERLY
00:52 mrdata 3V / 300 mA -> 10 ohm?
00:52 rue_mohr2 10V 300mA
00:52 rue_mohr2 for the led
00:52 mrdata yeah, the R will drop 3V at 300 mA say
00:52 GargantuaSauce the dropout is a function of current rue_mohr2
00:52 GargantuaSauce that's why it's not in the table
00:53 mrdata it's in the curve fig.10
00:53 GargantuaSauce oh yes you said that
00:53 rue_mohr2 ohm -v 0.7 -i 0.3
00:53 rue_mohr2 Wattage is: 0.210000
00:53 rue_mohr2 Current is: 0.300000
00:53 rue_mohr2 Voltage is: 0.700000
00:53 rue_mohr2 Resistance is : 2.333333
00:53 GargantuaSauce i should read more before responding
00:53 mrdata oh, 2V drop / .3A -> 6.6 ohm
00:53 rue_mohr2 a bipolar with a 2.3 ohm resistor
00:54 rue_mohr2 GargantuaSauce, the datasheet mrdata found is better than the ones I have
00:55 GargantuaSauce yes onsemi makes nice ones
00:56 GargantuaSauce some of TI's for generic parts are aawfuul
00:56 rue_mohr2 I bought china ones marked "ST" in a squiggly font :)
00:56 rue_mohr2 they might just be peices of plastic with metal pins glued to them
00:57 GargantuaSauce also in this decade you should be doing switching supplies!
00:57 GargantuaSauce heh
00:57 rue_mohr2 yea, dont want ot design one, cant find any that are suitable
00:59 GargantuaSauce use an adjustable buck converter and replace the pot with a current sense resistor
00:59 GargantuaSauce basically exactly as you were looking to use the lm317
01:00 rue_mohr2 yes, but now you need a filter
01:00 GargantuaSauce not necessarily
01:00 rue_mohr2 my mind went thru a few op-amp based solutions
01:00 rue_mohr2 origionally I wanted a boost supply
01:00 rue_mohr2 none are available premade on ebay that have current limiting
01:00 Hyratel actually
01:00 rue_mohr2 because the system I'm using it on is 6V
01:01 rue_mohr2 well, one of them
01:01 Hyratel for LED dimming, you want to use a CC driver and PWM that on/off
01:01 rue_mohr2 I ust want fixed 300mA
01:03 rue_mohr2 okok, an NPN bipolar, a 1k BC pullup, two silicon diodes, and a 2.3R sense resistor
01:04 rue_mohr2 dropout should be about 0.9V
01:04 rue_mohr2 the battery min is 10.5
01:04 rue_mohr2 so at 10.9 you start to notice it drop
01:04 rue_mohr2 from 13.5 it will be a while
01:05 rue_mohr2 ?
01:06 GargantuaSauce it's probably a good thing if it starts to draw less current (and notify the user) as the battery gets low
01:06 rue_mohr2 its an emergency light, its irrelivent
01:06 GargantuaSauce since you don't want to run lead-acid all the way down anyway
01:06 GargantuaSauce ah
01:06 rue_mohr2 http://fourier.eng.hmc.edu/e84/lectures/figures/differential_amplify.gif <<- right image, but with 2 diodes
01:06 GargantuaSauce all the more reason to be anal about efficiency!
01:07 rue_mohr2 yea, ALL emergency lighting uses incadescent bulbs...
01:07 rue_mohr2 mine is non-critical, but I thought I'd made it led, just cause
01:07 rue_mohr2 right now its 9W @ 12V on one system and 9W @ 6V on the other
01:07 GargantuaSauce when ivan nukes seattle your leds will be fried though!
01:08 rue_mohr2 pff
01:08 rue_mohr2 so I'm dealing with .75A/bulb on the 12V system
01:09 rue_mohr2 going to .3A and losing some efficiency is still a big improvement
01:10 mrdata "<rue_mohr2> WHY DO i RUSH OUT AND BUY THE PART FROM EBAY BEFORE TESTING THE IDEA PROPERLY" -- if i had $1 for every time i did this ...
01:10 rue_mohr2 haha
01:10 rue_mohr2 you still woulnd't be a millionare :)
01:10 mrdata no, but at least i have a bunch of spare parts
01:10 rue_mohr2 yea
01:10 mrdata some of which turned out to be useful later
01:11 rue_mohr2 I bought 20 LM317
01:11 rue_mohr2 50 3.9R resistors
01:11 mrdata can still be quite useful
01:12 rue_mohr2 course 3.9R is for 1.2V sense, the lm317 is really 1.25, which means using 4.2R
01:12 data hasnt taken inventory la
01:12 rue_mohr2 ...
01:12 rue_mohr2 I dont have lots of really low resistance resistors
01:12 mrdata next order, get a variety
01:12 GargantuaSauce http://www.ebay.ca/itm/251445874204
01:13 GargantuaSauce part assortments are one of my vices
01:13 rue_mohr2 hmm
01:13 rue_mohr2 most of the high power ones I have are 1k and up
01:14 GargantuaSauce no 4.2 in that but it's still a good variety
01:14 rue_mohr2 so that wouldn't be a waste in that sense
01:14 rue_mohr2 http://www.ebay.ca/itm/2-3-4-5-6-DOF-Mechanical-Arm-Steering-Gear-Bracket-Mechanical-Claw-Robotic-NEW-/231301094469
01:14 rue_mohr2 ahhahaha
01:14 rue_mohr2 how many dof of your arm do you want today?
01:15 rue_mohr2 $73? rllY!? seems pretty high
01:15 GargantuaSauce yeah doesnt even include servos
01:15 rue_mohr2 damn
01:15 rue_mohr2 didn't notice that
01:15 GargantuaSauce think low-volume machining for stuff like that isnt very cost effective
01:16 rue_mohr2 from china too
01:16 GargantuaSauce well yeah. chinastuff is only cheap because volume
01:16 GargantuaSauce and you arent gonna sell 10 million shitty servo arms
01:16 rue_mohr2 http://ruemohr.org/~ircjunk/robots/arm8/p1060649.jpg
01:16 rue_mohr2 that project cost...
01:16 e_mohr2 th
01:16 GargantuaSauce and how many hours of tooling and labour? :)
01:17 GargantuaSauce if you were gonna sell it what would be the price
01:17 rue_mohr2 2.50+(3.50*5)+2.60
01:17 rue_mohr2 so about 23 bucks
01:18 rue_mohr2 at the rate I'm making them, its getting cheaper
01:18 rue_mohr2 so, technically its an overbudget project (budget is $20) but I'm happy with the result
01:18 GargantuaSauce hehe
01:18 rue_mohr2 (well I'm not happy with anything that I made, but I know its ok)
01:19 rue_mohr2 I'm allowed to go up to 200% over budget
01:20 rue_mohr2 is 15% over...
01:20 rue_mohr2 it'd be lots more if I'd used one of my $8 mega32 instead of a $2.60 m328 board
01:27 rue_mohr2 http://www.ebay.ca/itm/2pcs-3D-LED-LightSquared-4x4x4-2-5-7MM-LED-Cube-White-LED-Blue-Ray-DIY-Kit-NEW-/231318473938
01:27 rue_mohr2 ahha I think thats one of the best howto-s I'v seen on ebay
17:45 deshipu https://www.youtube.com/watch?v=gNedhwvKjQg
17:45 deshipu almost there
20:20 GargantuaSauce nice deshipu. i would not have thought a 2dof quadruped would work at all
20:20 GargantuaSauce you defintitely need grippy feet!
20:22 GargantuaSauce as for dealing with the wires, i would just cut them and put on new connectors
20:22 GargantuaSauce get a big chunk of ribbon cable and some dupont connectors and a crimper and replacing them as necessary will be straightforward
20:29 GargantuaSauce though a few loops and cable ties can also go a long way
21:44 Hyratel https://www.facebook.com/hormestherobot/timeline
23:04 zhanx evening
23:05 GargantuaSauce 'lo
23:10 zhanx how go it]
23:17 GargantuaSauce it goes