That’s interesting, so you can flip the relays all you like without trouble as long as the 24DC supply isn’t connected? If that’s true then your problem presumably isn’t the typical inductive kick from the relay coil. It looks like your relay board has stuff on it which is presumably drivers and snubbers so let’s assume all of that is adequate to the job.
So, if it’s inductive kick from the valve solenoid it’s being coupled all the way from there, back through the 24DC supply to the outlet, then forward through the USB supply to your shift register, which is impressive! But not implausible.
Anyway, three places I’d add some stuff:
The main thing you need is a snubber network across the valve solenoid coil itself, ideally physically close to the valve (you want to minimize the area of the loop formed by the valve coil - wiring - snubber). Something as simple as a freewheel/clamping diode would probably help a lot. This will also improve the lifespan of your relay contacts which are probably arcing a little.
Small decoupling cap on your breadboard, say 0.1µF on the power supply rails, to keep your logic happy.
Larger decoupling cap on your 24VDC rails (the bus on the left), just to eat any transients the snubber doesn’t deal with. Maybe 1-10µF or so?
Thanks for your thoughtful response… and sorry it took so long to get back to you. I tried different combinations of capacitors, a diode on the load lines, etc… nothing worked. And then I put a 0.1uF capacitor directly between the power leads on the valve itself… and everything started working fine. Admittedly, I’m not 100% sure why… but I won’t complain :)
That makes sense, it forms a simple snubber network. A capacitor in series with a low-value resistor might work even better. Did you try a freewheeling diode directly across the valve leads?
Not entirely sure, but maybe these help you somehow:
The relay has a coil which requires 0.35W. The chip seems to have a maximum output current of 35mA.
The ‚switch on current‘ of an inductive load is usually 3 to 5 times higher than the ‚hold‘ current.
The valve may not have a free-wheeling-diode. This could create an issue by creating strange voltage spikes on all your supply voltages (connected by GND).
Yeah, decoupling cap here might as well just help OP fry the chip more effectively by ensuring it can sink all that current.
Solution here is probably a transistor/MOSFET that the chip turns on, which in turn turns on the relay. Relay coils are inductors, so that probably also needs a diode to protect the transistor from inrush current and also the kickback when it turns off: inductors resist changes, so it’ll try to keep sinking the current and result in temporary spike of very high voltage: spinningnumbers.org/a/inductor-kickback.html
I recommend EEVBlog’s OpAmp tutorial. His explanation is pretty simple to understand. Basically there are two rules (note these rules are ideal, but the exceptions can usually be ignored):
No current flows into the inverting and non-inverting inputs.
For negative and positive feedback circuits, the OpAmp wants to keep the inputs the same by changing its output, and will sink power to its positive or negative power rails to achieve this.
The oscillator is creating both DC and AC. The DC component is the average value of the signal. In the case of your 0-10v square wave, that is 5v. The AC compnent is the part of the signal that changes. The effect of the capacitor is to block the DC component, leaving only the AC component. The waveform is shifted vertically to be centered around 0v.
pressfit connections usually are very reliable. if there is a poor connection i would presume that the barrel of the via is broken and a new pressfit connector will not help. maybe putting solder in would help. did you already test for poor connections?
Barrel of the via? I’m unfamiliar with that terminology – what is that? I did a continuity check from the very bottom to the very top and everything tested good. When the audio is out, twisting the header a bit would usually bring it back so I assume(d) it was just a poor connection somewhere despite the continuity check.
EDIT: Okay, some quick Googling got me understanding this better. As I mentioned, continuity is good, but I still suspect it’s something in this area. I suppose I could remove the connectors and install solder connectors, instead of press fit?
yes i think so, but u would have to make sure the solder will rise through the through-hole as mich as possible. maybe u can try to find the faulty pin with wiggling them separately
The standard way of looking at this is to consider a capacitor-resistor series combination going to ground. Connect a 10v (wrt ground) supply to the capacitor and the voltage across the resistor rises to +10v, then decays. Now connect that capacitor to ground and that same resistor gets -10v across it, which then decays. Whatever is connected to the capacitor “top” terminal has to be able to sink current as well as source it.
That’s what generators in simulators do - they have zero internal impedance (usually). They sink currents as well as source them.
That’s why they call it a decoupling capacitor, cuz you usually just need AC (signal) at the out of a circuit, you don’t need the DC part of the signal.
True AC is sort of “balanced” in that it has just as much positive as negative. The positive area of the waveform is the same size as the negative area. For waveforms that are sort of symmetric across the 0V with a time offset, such as a sine or square wave, this means that it is centered along the 0V line. A DC source, on the other hand, never changes voltage.
The 0V to +10V source you have is actually a -5V to +5V square AC plus a +5V DC. The capacitor is getting rid of the DC component leaving just the AC, which happens to be the -5V to +5V AC that you are getting.
In my opinion an oscillator always produces an AC sine wave. There is usually no need for a DC overlapped oscillator signal. The DC supply of an oscillator produces a AC sine wave relative to GND.
Where exactly did you measure a DC sine wave, relative to what, and what do you mean by “AC removes a DC component”?
I think that it is the same stuff, just will propellant added in the aerosol. A small squeezy bottle with a needle is better if you have live stuff nearby - but you can always fill one from an aerosol
Even after you manually wiped using the links in your archive? If you just used PDS though it might be that reddit did some reindexing to make older stuff show up again, or a sub or a few going unprivate.
Nah it’s 13K comments, I can’t wipe them all manually. It could be as you say that PDS doesn’t see comments in private subs. In that case I’ll need to find something that lets me feed it all the links.
Thanks. There’s been a lot of talk lately about comments not being properly deleted or Reddit restoring them after deletion. But I figure I can just run PDS multiple times over the next couple of weeks to get the ones that it didn’t catch on the first run. In any case, the “comments” section in my profile comes up empty right now.
I did do a full export through the request form on Reddit before going through with this. I had a total of 13K comments to wipe.
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