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2015-01-28 03:25 <whitequark> hey wpwrak_ DocScrutinizer05
2015-01-28 03:25 <whitequark> so there's a circuit like this: https://pbs.twimg.com/media/B8aAls9CEAIlrhs.png:large
2015-01-28 03:25 <whitequark> when SW1 is closed, the MCU input connected to SW2 (normally open) trips spuriously
2015-01-28 03:28 <DocScrutinizer05> hmm
2015-01-28 03:29 <whitequark> the solenoid at the right is actually a pinball machine flipper
2015-01-28 03:29 <whitequark> http://stevechannel.com/eos.htm
2015-01-28 03:29 <DocScrutinizer05> (sorry, sick. maybe there's some old slivers where my brain should be)
2015-01-28 03:29 <whitequark> what I don't really understand is,
2015-01-28 03:29 <whitequark> even if the high transient currents in the wiring to the solenoid induce voltage elsewhere
2015-01-28 03:29 <DocScrutinizer05> ooh pinball, now you got my full attention
2015-01-28 03:29 <whitequark> it shouldn't happen to a wire that is essentially floating
2015-01-28 03:29 <whitequark> and pulled down on the MCU side (10k on-chip resistor)
2015-01-28 03:31 <DocScrutinizer05> it will
2015-01-28 03:31 <whitequark> how'd that even work? you do not have a closed path
2015-01-28 03:32 <whitequark> i mean, there's probably some parasitic capacitance between that wire and MCU ground
2015-01-28 03:32 <whitequark> a few dozen pF at most
2015-01-28 03:32 <whitequark> and it IS pulled down, not just floating
2015-01-28 03:32 <DocScrutinizer05> actually EOS is to force high current through solenoid until it moved to end position. Then the contact opens to reduce current flowing through solenoid
2015-01-28 03:32 <whitequark> yep, that much I gathered
2015-01-28 03:32 <whitequark> it should consume 8A@30V for a few ms
2015-01-28 03:33 <DocScrutinizer05> (unrelated mostly to the problem here)
2015-01-28 03:33 <DocScrutinizer05> :nod:
2015-01-28 03:33 <whitequark> the layout is
2015-01-28 03:33 <whitequark> gnarly
2015-01-28 03:33 <whitequark> http://zacaj.com/screenshots/2015-01-27_21-57-28.jpg
2015-01-28 03:34 <whitequark> but i guess that's inevitable
2015-01-28 03:35 <DocScrutinizer05> yep
2015-01-28 03:36 <whitequark> so, any ideas what can be done to fix the spurious SW2 trips?
2015-01-28 03:37 <DocScrutinizer05> have the pair(!) of wires from MCU to sw2 twisted, keep them away from other high current wires. Increase load (inside MCU) to 1k or less, add a RF capacitor and naybe a ferrite bead
2015-01-28 03:38 <whitequark> ok, so what i suggested to her wasn't wrong...
2015-01-28 03:38 <DocScrutinizer05> that's RF interference, not capacitive phantom current
2015-01-28 03:38 <whitequark> hmm
2015-01-28 03:38 <DocScrutinizer05> SW1 creates lots of RF noise
2015-01-28 03:38 <DocScrutinizer05> actually EOS switch, not sw1
2015-01-28 03:39 <whitequark> putting a snubber on EOS switch also didn't do anything to mitigate this
2015-01-28 03:39 <whitequark> apparently
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2015-01-28 03:40 <whitequark> RF capacitor where?
2015-01-28 03:40 <whitequark> across the solenoid?
2015-01-28 03:41 <DocScrutinizer05> bead and 47pF on MCU input
2015-01-28 03:41 <whitequark> right
2015-01-28 03:42 <DocScrutinizer05> also consider the magnetic field of solenoid
2015-01-28 03:53 <DocScrutinizer05> whitequark: what is sw1?
2015-01-28 03:54 <DocScrutinizer05> I assumed it was related/mounted to flipper solenoid. Maybe it's not at all?
2015-01-28 03:54 <DocScrutinizer05> err sw2, sorry
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2015-01-28 03:54 <whitequark> sw2 is a button on the photo
2015-01-28 03:55 <DocScrutinizer05> ?
2015-01-28 03:55 <whitequark> http://zacaj.com/screenshots/2015-01-27_21-57-28.jpg
2015-01-28 03:55 <whitequark> so it's not mounted on solenoid
2015-01-28 03:55 <DocScrutinizer05> which button?
2015-01-28 03:55 <whitequark> see the red wire at bottom?
2015-01-28 03:56 <DocScrutinizer05> yes
2015-01-28 03:57 <DocScrutinizer05> well, "wire"
2015-01-28 03:57 <whitequark> it closes red/green (ignore blue, it doesn't exist)
2015-01-28 03:57 <whitequark> and so switches on the solenoid
2015-01-28 03:57 <DocScrutinizer05> sw2?
2015-01-28 03:58 <whitequark> sw2 yes
2015-01-28 03:58 <DocScrutinizer05> and what's sw1 then?
2015-01-28 03:59 <whitequark> another unrelated switch elsewhere
2015-01-28 03:59 <DocScrutinizer05> err
2015-01-28 04:00 <DocScrutinizer05> so how does sw2 switch on the solenoid?
2015-01-28 04:00 <whitequark> crap\
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2015-01-28 04:00 <whitequark> i mixed these up
2015-01-28 04:01 <whitequark> SW1 is the red button on the photo
2015-01-28 04:01 <whitequark> SW2 is a switch elsewhere
2015-01-28 04:01 <DocScrutinizer05> where?
2015-01-28 04:02 <whitequark> sec
2015-01-28 04:02 <DocScrutinizer05> make sure neither of both contacts of SW2 has connection to any GND or huge metal area
2015-01-28 04:03 <DocScrutinizer05> make sure the wiring from MCU to SW2 is twistet pair
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2015-01-28 04:04 <whitequark> DocScrutinizer05: so, this is zacaj's pinball machine
2015-01-28 04:05 <DocScrutinizer05> also make sure MCU and solenoid don't share GND wiring
2015-01-28 04:05 <whitequark> zacaj: where's SW1 located?
2015-01-28 04:05 <whitequark> er SW2
2015-01-28 04:05 <whitequark> the one connected to MCU input
2015-01-28 04:06 <zacaj> there's a whole bunch,\ all over the playfield
2015-01-28 04:06 <DocScrutinizer05> roll over buttons?
2015-01-28 04:06 <zacaj> my MCU and my solenoids need to share GND at some point so that I can control them via MOSFETs
2015-01-28 04:06 <DocScrutinizer05> or taget or sth
2015-01-28 04:07 <zacaj> yes, rollovers, targets, etc
2015-01-28 04:07 <DocScrutinizer05> sure connect GND, but don't share wiring
2015-01-28 04:07 <zacaj> I have them connected at one point near the PSUs
2015-01-28 04:07 <DocScrutinizer05> star topology
2015-01-28 04:07 <zacaj> no, not shared
2015-01-28 04:07 <zacaj> just wanted to clarify/make sure
2015-01-28 04:07 <zacaj> yep
2015-01-28 04:07 <DocScrutinizer05> good
2015-01-28 04:08 <DocScrutinizer05> you built MCU?
2015-01-28 04:08 <DocScrutinizer05> or at least know it?
2015-01-28 04:08 <zacaj> it's an STM32F3DISCOVERY (http://www.st.com/web/catalog/tools/FM116/SC959/SS1532/PF254044)
2015-01-28 04:08 <DocScrutinizer05> what's the input ?
2015-01-28 04:08 <zacaj> what do you mean?
2015-01-28 04:09 <DocScrutinizer05> GPIO with nothing else? opto coupler? relay coil?
2015-01-28 04:09 <DocScrutinizer05> GPIO with added pull down resistor?
2015-01-28 04:10 <zacaj> it's just the wire running from the switch to the GPIO, with an internal pulldown
2015-01-28 04:10 <DocScrutinizer05> eeek
2015-01-28 04:10 <zacaj> I tried adding a 10k external pulldown, and it didn't affect it at all
2015-01-28 04:11 <DocScrutinizer05> add a 500R pulldown, and proper clamping diodes to + and GND, and from that a 10k to GPIO
2015-01-28 04:12 <DocScrutinizer05> or 4k7
2015-01-28 04:12 <DocScrutinizer05> GPIO are not made for that sort of input signals, really
2015-01-28 04:12 <DocScrutinizer05> you need to add some protective and impedance matching gear
2015-01-28 04:13 <DocScrutinizer05> ideally use opto couplers
2015-01-28 04:14 <DocScrutinizer05> actually the contacts of SW2 *need* a certain minimum current to keep them clean
2015-01-28 04:14 <zacaj> so this level of spikes and interference from the coils is standard, (eg best I'm going to get) and I should be attempting to smooth it off in various ways at the inputs, instead of trying to lower the source of the interference?
2015-01-28 04:14 <DocScrutinizer05> yes
2015-01-28 04:16 <zacaj> alright..  some of my inputs go through a shift register, and they seem to work fine, so for the inputs I guess I could just re-route all my GPIO ones through that.
2015-01-28 04:16 <DocScrutinizer05> honestly I strongly recommend using opto couplers for this. Particularly for this environment
2015-01-28 04:17 <DocScrutinizer05> otherwise I wouldn't take bets on how long your chip will live
2015-01-28 04:17 <zacaj> I'm also having trouble with my LED driver chips 'randomizing' sometimes when I flip, is there anything besides sticking some decoupling capacitors on I could do for that?
2015-01-28 04:17 <DocScrutinizer05> it deteriorates from the harsh input signals you encounter in a high current + solenoids environment like this one
2015-01-28 04:18 <DocScrutinizer05> generally try going low impedance design
2015-01-28 04:18 <DocScrutinizer05> use capacitors everywhere to clamp high frequencies (on digital signals)
2015-01-28 04:19 <DocScrutinizer05> use termination resistors in the range <1k on all inputs
2015-01-28 04:20 <DocScrutinizer05> design for mechanical switches like SW2 at least dealng with 20mA load
2015-01-28 04:20 <DocScrutinizer05> i.e. even lower termination resistors
2015-01-28 04:24 <whitequark> hm, clever
2015-01-28 04:25 <zacaj> alright, thanks.  I'll give some of that a shot
2015-01-28 04:28 <DocScrutinizer05> and check about "self cleaning current" of contacts. I dunno if I vcan find the right wiki article right away. generally open contacts need a certain minimum current they have to switch, so any oxide etc will "burn away". Otherwise they eventually start failing
2015-01-28 04:29 <DocScrutinizer05> "open" as in "not sealed"
2015-01-28 04:30 <DocScrutinizer05> a reed contact in a glass tube with inert gas has few requirements like those. The contacts you deal with in your pinball cabinet need some tens of mA at least to stay "fresh"
2015-01-28 04:34 <DocScrutinizer05> oooh, btw: those glitches on sw2 even might be triggered by mechanical vibration, particularly when the contacts have insufficient load as elaborated in lines above. This would be a typical problem of contacts building up issues without self cleaning
2015-01-28 04:35 <DocScrutinizer05> you might test the conductivity (Ohms) of SW2 and see if it has some increased R_closed already
2015-01-28 04:37 <DocScrutinizer05> this would be a noisy effect seen every now and then, so a single short time test may not tell much, you need to probe the thing several times, opening and closing it slowly and gently. Ideally using a scope to see excessive bouncing etc
2015-01-28 04:38 <zacaj> I tested with SW2 disconnected completely from the GPIO and I'd still get glitches
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2015-01-28 04:40 <DocScrutinizer05> ((trouble with my LED driver chips 'randomizing')) use proper 47pF 22nF supply voltage buffering next to the chips. Consider shielding of the whole circuit, eg. with a alu coated carton you place on the soldering side of PCB and connect the ALU to GND
2015-01-28 04:40 <DocScrutinizer05> ((still glitches)) ooh on MCU?
2015-01-28 04:41 <DocScrutinizer05> i.e. the MCU glitches even on GPIO that are not connected to any wires?
2015-01-28 04:41 <zacaj> yes
2015-01-28 04:41 <DocScrutinizer05> if yes, you need to test of it still does when you short the input to GND
2015-01-28 04:42 <DocScrutinizer05> and you should consider proper shielding of your MCU PCB
2015-01-28 04:42 <zacaj> short the switch, or the GPIO?
2015-01-28 04:43 <DocScrutinizer05> and make sure your power supply is clean: place some huge ferrite bead on VDD wire, next to the MCU, and a buffer capacitor behind that
2015-01-28 04:44 <DocScrutinizer05> you said the GPIO is not connected to any wires and still gets glitches. So short to GND the PCB connection point where wire would go
2015-01-28 04:46 <DocScrutinizer05> that's the brute force low inpedance design ;-) When it still sees glitches even when GPIO grounded, we face another problem
2015-01-28 04:47 <DocScrutinizer05> if grounding fixes the problem, it's clearly cause by electromagnetic interference and can get fixed by appropriate measures
2015-01-28 04:47 <DocScrutinizer05> like low impedance termination, i.e. a 470R from GPIO input to GND
2015-01-28 04:48 <DocScrutinizer05> 220R maybe, to give the contacts something to work with (self cleaning)
2015-01-28 04:49 <DocScrutinizer05> assuming this 3.3V in that drawing is correct
2015-01-28 04:49 <zacaj> yeah, 3.3v
2015-01-28 04:50 <DocScrutinizer05> in addition you want a 47pF and a 100nF parallel to that 220R. And optimum would be a 10kR from all that to the real GPIO
2015-01-28 04:51 <DocScrutinizer05> hmm, rather place the 100nF parallel to SW2
2015-01-28 04:52 <DocScrutinizer05> close to sw2
2015-01-28 04:52 <DocScrutinizer05> iow at far end of the twisted pair wire
2015-01-28 04:54 <zacaj> 'real GPIO'?
2015-01-28 04:54 <DocScrutinizer05> but still such design has a lot of "antennas" feeding all sort of noise to your MCU GND
2015-01-28 04:55 <DocScrutinizer05> CHIP GPIO <-10kR-> C-toGND, R-to-GND <---wire------
2015-01-28 04:56 <DocScrutinizer05> (noise to MCU GND) or to VDD 3V3 in your case
2015-01-28 04:56 <zacaj> k, that's what I thought
2015-01-28 04:57 <DocScrutinizer05> opto couplers are a sure bet to fix all issues of such design
2015-01-28 04:58 <DocScrutinizer05> just use "separate" GND and VDD for external side of couplers
2015-01-28 04:59 <whitequark> and same solution for MOSFETs
2015-01-28 04:59 <DocScrutinizer05> ideally yes
2015-01-28 05:01 <zacaj> k, thanks.  I'm off to bed
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2015-01-28 10:42 <nicksydney> whitequark & wpwrak_ :  https://www.kickstarter.com/projects/1133560316/black-swift-tiny-wireless-computer
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2015-01-28 12:49 <wpwrak_> nicksydney: cute ;-) and even open hw. btw, you should make a kickstarter project to create a taxonomy of all those little boards :)
2015-01-28 12:50 <nicksydney> wpwrak_: heheheh.....no need http://www.cnx-software.com/ already have the list :)
2015-01-28 12:52 <wpwrak_> but you could format it nicely :) break it down into tables comparing features, etc. that's more work that one may think
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2015-01-28 13:14 <nicksydney> wpwrak_: maybe i should start a wiki page for that
2015-01-28 13:14 <nicksydney> will do that in qi-hardware website later
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2015-01-28 15:43 <kristianpaul> https://www.sparkfun.com/products/13167
2015-01-28 15:43 <kristianpaul> sb0
2015-01-28 15:44 <sb0> "optionally, could support a Si Avalanche Photo-Diode (APD)"
2015-01-28 15:44 <sb0> are those going to be less expensive?
2015-01-28 15:47 <kristianpaul> dont know
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