#garfield Logs

Jul 06 2015

00:06 rue_shop3 strawberries cant be worth that much power bill
00:08 any69168222 you'd be surprised
00:08 any69168222 and becaue "you get what you pay for", some people pay way too much for organics
00:08 rue_shop3 ok , the voltage ref is from 1.25 to 3.75V
00:08 rue_shop3 the output is 0-30V
00:08 rue_shop3 if I make a voltage divider that has the bottom offset to 1.25V
00:10 rue_shop3 arg
00:10 rue_shop3 if the ... I cant just pick up the bottom of the divider
00:10 rue_shop3 its got to be mirrored around something
00:11 any69168222 why>
00:11 rue_shop3 think on this
00:11 rue_shop3 Vout ----/\/\/\/----Vfb------\/\/\/\/\----1.25V
00:12 rue_shop3 when Vout is 30, Vfb is 3.75
00:12 rue_shop3 so if the right resistor is 1k, that makes the left one 7k
00:12 rue_shop3 all good
00:12 rue_shop3 now, if the output goes to 0V, the vfb will be less than 1.25
00:12 any69168222 6.8k is normal, 7k may be hard to find
00:13 rue_shop3 trim ports
00:13 rue_shop3 pots
00:13 any69168222 umm, you haveto scale both
00:13 rue_shop3 simotanious equation I think
00:14 rue_shop3 I cant bite into one of those right now
00:14 any69168222 this is what makes your situation scream for psu 5v over and under the 0v-30v range, and an opamp that won;t blow up with those voltages
00:15 any69168222 so get a 60v opamp, a 555 charge pump just for the opamp and Vrefs, and you're all done
00:16 rue_shop3 I'm sure I can just out-clever it
00:16 any69168222 i got some "sharp cheddar" the other nite, it's so bland i cannot tell it from the "american" cheese, except it seem oiler and is glossy and limp
00:17 any69168222 i believe the charge pumps will be simpler than wasting brain cells on getting opamps and zeners and current sourses to do scaling and offsets
00:18 any69168222 having the 60v opamp willmake the design less likely to oscillate and have other querks too
00:19 any69168222 the 60v opamp will easily operate over the entire 30v range of the psu with no gimmicks or fudges to trick it
00:21 any69168222 use a $8 15v laptop brick and a tripler to make 45v at an amp for the opamp and Vrefs and output driver, and it's all textbook str8 easy from there
00:22 any69168222 so i took the "american" and sprinkled pepper on it, folded it, peppered it again, folded it, peppered again and folded it, and it beats the heck outa this so-called "sharp cheddar" for bite
00:24 y69168222 ponders other spices, and simply layering instead of fol
00:25 any69168222 diy pepperjack, sorta
00:25 any69168222 times like this i wish Tiggr was up and alive and could use all her data, because on one of these drive sitting around here is the recipie for half a dozen pepperjacks
00:26 rue_shop3 its like forging a sword
00:26 any69168222 having a bot that knows river gravel is not an ingredient in food could be an asset some day
00:34 any69168222 i think i'd put more into Tiggr working if others also considered that a wonderful goal
00:34 rue_shop3 hah! I think I got wolfram alpha to solve it
00:35 any69168222 wolfram don;t do schematics
00:35 rue_shop3 http://www.wolframalpha.com/input/?i=c%3D%28f-a%29%2Fd%2C+f%3D3.75%2C+c%3D.002625%2C+x%3D%28y-a%29%2Fd%2C+x%3D-0.000125%2C+y%3D1.25
00:35 rue_shop3 :)
00:35 rue_shop3 asking was hard
00:36 rue_shop3 the result says that the bias voltage should be 1.3636V and the bottom resistor (given the top one is 10k) should be 909.1ohms
00:36 rue_shop3 actaully, asking WAS the hard part, I could have solved the rest myself
00:37 any69168222 clever programming, that bot is
00:38 rue_shop3 what I like best is that if its not solvable, it tells me immediatly with a complex answer
00:38 rue_shop3 opposed to me burning up 5 hours and a ream of paper
00:38 any69168222 is that like "bs in, bs out" ?
00:50 rue_shop3 yea
00:50 rue_shop3 something is wrong tho
00:50 rue_shop3 the plot dosn't work
00:50 rue_shop3 checking things...
00:51 rue_shop3 oh damn
00:51 rue_shop3 it dosn't work, I dont know what went wrong
00:52 rue_shop3 but I know how to solve it now
00:52 any69168222 it out-clevered you
00:53 rue_shop3 Vout ----[R2]----Vfb------[R1]----Voffset
00:53 rue_shop3 I set R2 to 10k arbitrarily
00:53 any69168222 after you have put so much hardware between the output signal, the Vref, and the opamp, and the pamp to output transistor, how well do you think it will work?
00:54 rue_shop3 I have two data points, Vout = 30, Vfb=3.75, and Vout=0, Vfb=1.25
00:54 rue_shop3 so I can work out the currents at the two points
00:55 rue_shop3 then, I know the current and the high voltage at the two points, and I can use simotanious equations to solve a resistance and votlage that make it work
00:55 e_shop3 grabs another page from the
00:55 any69168222 simULtaneous
00:56 any69168222 wtf, you got a job and i don't, it must be simotanious, nm
00:56 rue_shop3 ooh found my error
00:56 rue_shop3 generic form of a voltage divider
00:56 rue_shop3 got it wrong
00:58 rue_shop3 it should have been Vfb=Voffset+R1((Vout-Voffset)/(R1+R2))
00:59 rue_shop3 I forgot the first Voffset
01:01 any69168222 should i tell zhanx?
01:01 zhanx Sure
01:01 any69168222 k, i-Cub was given a virtual version of itself, which it runs in parallel to ther eal world, and can cmpare the expected behavior in the VR to itself in the real
01:02 any69168222 this also improves the VR as i-cub reprograms it, makingit a perfect raining vr for other robots
01:03 zhanx Nice
01:04 rue_shop3 haha!
01:04 rue_shop3 the solution wasn't wrong, the check was!
01:04 zhanx The debug was off
01:05 rue_shop3 http://www.wolframalpha.com/input/?i=V3%3D1.3636%2B0.0833*%28V1-1.3636%29%2C+V1from+0+to+30
01:05 rue_shop3 oh yea! oh yea!!!!
01:05 rue_shop3 what a PITA!
01:05 y69168222 pats rue on the
01:05 rue_shop3 ok, now I have a voltage divider that puts everything in the operable range of all the parts I have
01:06 rue_shop3 I dont like the fact its so narrow, but nothing is really gonna help that
01:09 rue_shop3 now, shal I do that for the 0-5V current signal?
01:10 any69168222 can't really say
01:10 rue_shop3 maybe not tonight
01:11 rue_shop3 I wonder how I should do the 1.3636V ref
01:12 any69168222 they make a part for that
01:12 rue_shop3 oh yea
01:13 rue_shop3 TL431
01:13 rue_shop3 or a LM317
01:13 any69168222 no
01:13 rue_shop3 which I think bottoms out at 1.25
01:15 rue_shop3 I'm off to bed
01:17 any69168222 i can't find it, it was a 1.3xxxx precision Vref, avail on ebay even
01:29 any69168222 well, that is screwy: using 20 pcs of IRF830 in parallel to rectify 20amps is no more efficient than using a plain ole diode
12:34 any38546743 "attempting to rej-o-in"
12:41 any38546743 rej-o-ine
18:01 -asimov.freenode.net:#garfield- [freenode-info] please register your nickname...don't forget to auto-identify! http://freenode.net/faq.shtml#nicksetup
22:12 rue_shop3 oooh kat!
23:53 zhanx On greater news today I got a washer and 2 microwaves. Cnc lathe? Cooks the wood to shape