#robotics Logs

Jul 08 2018

01:01 AM rue_shop4: hmm
01:05 AM rue_shop4: yer not gonna have me measuring the Bsat of my ferrite again are ya?
01:05 AM rue_shop4: thats a rabbit hole I dont need to go down again...
01:05 AM rue_shop4: dont even know what I did with the math for that
01:05 AM rue_shop4: I think thats what lead to one of the breadboards getting scortched
01:15 AM rue_shop4: ok, two more oscillators to try first
01:26 AM mrdata: i doubt you will go into saturation
01:26 AM mrdata: at > 10 MHz and a few volts
01:26 AM mrdata: typical Bsat for ferrites is around 0.4 tesla
01:28 AM mrdata: coil current is well below max as fasr as i can tell; this isnt a power transmitter
01:29 AM mrdata: rue_shop4, but what is the actual cross-sectional area of the ferrite stick you have?
01:29 AM mrdata: i've done calculations with 60 to 80 mm^2
01:32 AM mrdata: max current with a 1 mm gap is 18 A; with 5.7 mm, it's 100 A
01:47 AM mrdata: sim says max coil current here is around 5 mA
01:48 AM mrdata: a margin of 20000x
02:11 AM mrdata: so that second 2n2222 ends up having a gain of about 6.6 at 17 MHz and more like 4 at 26 MHz
02:32 AM rue_shop3: hah, ok, I have to be carefull, in that last circuit, the scope probe was consitituting 70% of the oscillator capacitance
02:32 AM rue_shop3: 10mm stick
02:33 AM rue_shop3: I got a second "rc" osc to 10Mhz
02:33 AM rue_shop3: its unadjustable tho
02:42 AM rue_shop3: oo I got it to 20M
02:50 AM mrdata: 10mm stick, square so 100 mm^2 area?
02:51 AM mrdata: if so, 18 turns is too many
02:51 AM mrdata: um, well maybe not?
02:52 AM mrdata: i'm getting a discrepancy on two different calculators
02:52 AM mrdata: so we'll just say, some adjustments will be needed
02:57 AM rue_: no round with two small flats :)
02:57 AM rue_: I can play
02:57 AM rue_: taking a quick look at mixers
02:57 AM rue_: looks like if I use some of the tiny RF ferrite cores I can makea simple diode mixer
02:58 AM mrdata: ok, if it's round then cross-sectional area is 78 mm^2
02:59 AM mrdata: all's well
02:59 AM rue_: zippo:/tmp# circle -d 10
02:59 AM rue_: Radius is : 5.000000
02:59 AM rue_: Diameter is: 10.000000
02:59 AM rue_: Circumfrence is : 31.415926
02:59 AM rue_: Area is : 78.539818
02:59 AM rue_: Sphere area: 314.159271
02:59 AM rue_: Sphere volume: 523.598755
02:59 AM rue_: sure
03:02 AM rue_: the approach would nonally need the mixer, but a low pass filter for the extra image
03:04 AM rue_: so were 17-26Mhz
03:04 AM rue_: mixed with 16Mhz
03:05 AM rue_: so the scrap bands will be at 33-42Mhz
03:05 AM rue_: we only want 10Mhz,
03:06 AM mrdata: yes, but you do still have the 16 MHz in there, so the low-pass has to remove that sharply enough
03:06 AM rue_: assume -6db/decade, and filter the noise down to....
03:06 AM rue_: after its mixed is it still there?
03:06 AM mrdata: i think so
03:07 AM mrdata: you get the two original frequencies and the sum and the difference, as far as i recall
03:07 AM rue_: I thought its just the sum and differnce
03:08 AM mrdata: in any case, i like butterworth filters
03:08 AM mrdata: but here's a filter design calculator, http://www.wa4dsy.com/filter/filterdesign.html
03:09 AM rue_: uh, did you pick 14Mhz cause its a radio thing? I see a bunch of 14Mhz in the ARRL boook
03:10 AM mrdata: no, it was my dead reckoning that 14 MHz was far enough away from 10 MHz
03:10 AM rue_: ah
03:11 AM mrdata: so a 3-component butterworth filter will bring 16 MHz down 12.5 dB
03:11 AM mrdata: if cutoff is 10 MHz that is
03:11 AM rue_: cutoff is just -3db tho, yes?
03:12 AM mrdata: 3dB is cutoff
03:12 AM mrdata: yeah
03:12 AM rue_: its too bad I cant find one ofthe SAW oscillators with workable numbers
03:12 AM rue_: I need to get the signal to a 74LS244 output driver
03:12 AM rue_: I wonder how much gain I'll need to make good with the schmitt
03:13 AM rue_: 8-|
03:14 AM mrdata: 74LS series wants low < 0.8V, high > 2.25 V, iirc; and you should be okay if you circuit can source or sink 20 mA ish
03:14 AM rue_: 244 has schmitt
11:10 AM veverak: https://hackaday.io/project/157890-hahandle/log/148932-v3-prototyped
02:44 PM rue_: mrdata, what if I make a high freq by staggering a stupid number of phases of a lower freq?
02:44 PM rue_: ah, I'd have to varry the stagger
02:50 PM rue_: so, I'd just need a 21 gang capacitor and a 500Khz oscillator....
02:50 PM * z64555 ponders about frequency dividers
02:50 PM rue_: oh well
02:50 PM rue_: freq division wont work,
02:50 PM rue_: say you have 50Mhz, you divide by 5 to get 10Mhz,
02:51 PM rue_: the next step, divide by 6, takes you down to 8.3Mhz
02:51 PM z64555: oh, no, this is for something different
02:51 PM rue_: ah
02:52 PM z64555: I've got a motor spinning too fast on a blender, was wondering if there was an electrical method to slow it down without it leading/lagging too much
02:52 PM rue_: put an opto on it, I ahve a tiny13 program that does pwm control
02:52 PM rue_: you give it 0-5V control signal
02:53 PM rue_: tho, right now its set up strickly as a buck converter
02:53 PM z64555: would require install of an DC power supply, tho
02:53 PM rue_: I use it on my cnc machine
03:00 PM rue_: mrdata, oh no,...
03:00 PM rue_: http://www.interfacebus.com/tapped-delay-line-14-pin.jpg
03:00 PM rue_: its a delay line I can hack
05:41 PM rue_shop4: iinteresting, almost any semiconductor, reverse biased, can act as a varactor to about 60% of its value
05:42 PM rue_shop4: best so far is 2sc945 @ 76%
05:42 PM rue_shop4: (reverse biased C-B, to 16.5V)
05:55 PM rue_shop3: haha, I have the winner upside down, smallest % is winner
05:55 PM rue_shop3: the 1N5818 just won by a landslide, 38%
05:55 PM rue_shop3: goal is 10%
06:01 PM rue_shop4: well, if I use the multiphasic delay method, I might not need 10%
06:05 PM rue_shop3: no, wait... 2sc4242 is the winner so far, at 30%
06:20 PM rue_shop3: oooo 2sc4020 @ 27%
06:20 PM rue_shop3: big power transistors are where its at
06:34 PM rue_shop3: I need to work on other things today, so I'm calling it, 2SC5027 varried to 26% of its capacitance
06:35 PM rue_shop3: runners up are 2SC4106 and 2SC4020 at 27%
06:35 PM rue_shop3: with the 4020 having the smaller capacitance value
06:45 PM rue_shop3: ok I'M WORKING ON THE PUMP FOR MY PARTS WASHER NOW
06:45 PM rue_shop3: arg
07:37 PM Tom_L: http://tom-itx.no-ip.biz:81/~webpage/cnc/temp/Skate_Truck2.jpg
07:37 PM Tom_L: http://tom-itx.no-ip.biz:81/~webpage/cnc/temp/Skate_Truck1.jpg
07:48 PM rue_shop3: ah
07:48 PM rue_shop3: he gonna code it humslf?
07:49 PM Tom_L: no
07:49 PM Tom_L: pretty tough to code a polyline
07:50 PM rue_shop3: did he draw it?
07:50 PM Tom_L: i did
07:50 PM rue_shop3: ooooh
07:53 PM Tom_L: 1st year competing in that category, not knowing the format to prepare.. he took 19th out of 65 in the national competetion which i thought was pretty good
07:53 PM SpeedEvil: :)
07:53 PM Tom_L: 1st in state
07:53 PM Tom_L: the national winner goes to russia in 19
08:09 PM rue_shop3: oh he won
08:09 PM rue_shop3: coool
08:09 PM Tom_L: state
08:09 PM Tom_L: 19th at national
08:10 PM Tom_L: of 65
08:15 PM rue_shop3: oh
09:10 PM rue_: I have to play with this a bit, but its an interesting path
09:11 PM rue_: take an osc that goes from 625Khz to 1.25Mhz, feed it into an 8 channel variable delay line with selectable xors on the taps (that act like a x1-x8 multiplier)
09:12 PM rue_: frist range is .625-1.25M, then 1.25M-2.5M then 2.5M -5M, then 5M to 10M
09:12 PM rue_: I dont like it cause a microcontroller has to juggle it all
09:12 PM rue_: but I'd like to know if I can make the variable multipler
09:13 PM rue_: I thnk the delay line can be used as the oscillator feedback too
09:13 PM rue_: have to think on that one, but for now, tig welding
09:15 PM rue_shop4: I htink if the total delay for the oscillator consists of the accumulated delay of all the channels, it would just work out
09:15 PM rue_shop4: 1.25Mhz is...
09:16 PM rue_shop4: 800ns
09:16 PM rue_shop4: so 8x 100ns delays
09:16 PM rue_shop4: no
09:16 PM rue_shop4: 8x50ns delays
09:16 PM rue_shop4: inverting delay line
10:34 PM mrdata_: rue_: rue_shop4 ham radio guys recommend this mixer, https://www.minicircuits.com/pdfs/ADE-1.pdf
10:44 PM rue_: is it made of $35 parts that will take me 3 months to get?
10:45 PM rue_: yes it is
10:45 PM rue_: drat
10:47 PM rue_: I'd love to see if digikey has it, but none of my browsers meet their securrity requirements
11:11 PM * z64555 researches AC motors a bit
11:14 PM z64555: hm, they run slower the more poles per phase there is...
11:16 PM z64555: wonder why that is
11:31 PM z64555: hm, whats this about a starter coil
11:50 PM z64556 is now known as z64555
11:51 PM mrdata: rue_, it's a chip; $5 i am told
11:58 PM z64556 is now known as z64555