Help designing EMI filter for 12V-170V Nixie power supply - Page 1
Forum section: electronics / beginners

author: Mighty Burger
author_rank: Regular Contributor
timestamp: September 12, 2021, 05:21:50 am
content: Hi all!I'm currently working on a re-design of my Nixie tube clock project. This new version has a 12V to 170V DC converter. I am using ThreeNeuron's "Pile O' Poo":https://threeneurons.wordpress.com/nixie-power-supply/hv-supply-kit/I've breadboarded and tested my circuit, and things seem to be going well! Here is my current circuit design. It consists of two boards. The board that will go on the bottom has the MCU and power supply. The top board has the nixies/nixie drivers.Things seem to be working well! I have a test program running with a single nixie tube, and I'm able to cycle through all the digits and even blank the nixie without a problem.However, there are large voltage spikes as a result of this power supply. Even though the circuit works I'm concerned these spikes could cause major EMI issues, if not instability with the MCU.Here are the waveforms I'm measuring. Channels 1, 3, and 4 of the oscilloscope. Note I was having some trouble getting consistent measurements with the amplitude of these spikes.YELLOW: 12V RailPINK: 5V RailBLUE: 170V RailZoomed out:Zoomed in:Zoomed in even more:When I first built this circuit I did not have any filtering. So components L1, C4, L3, R4 and C8 were nonexistent. I saw these voltage spikes:12V Rail: 5V PK-PK170V Rail: 20V PK-PK(I did not measure the 5V rail.)Now, I had made a forum post a while back regarding my old design which used a 170V module off Ebay. I had similar EMI concerns. Tim gave me some advice (reply #85:https://www.eevblog.com/forum/beginners/32-768khz-pierce-crystal-oscillator-for-nixie-clock/85/) on a filter to add, and he gave his thought process behind it. (Thank you Tim!) I decided to use these same recommendations here, as the setup is similar. The filter is comprised of L1, C4, L3, R4, and C8.After adding these, the spikes did drop significantly, however they are still very large:12V Rail: 1.5V PK-PK170V Rail: 6V PK-PK5V Rail: 800mV PK-PKAfter this I tried a couple different things, including adding a 3.3uF cap after L3 (so in parallel with R4 and C8), as well as adding a 10uF cap after L1 but before R2. Neither had any significant effect.I was wondering if I could get some advice on how to suppress these spikes more?Now, I am inexperienced and had some trouble following along with Tim's thought process. Reading again I believe he suggested adding some resistors in series with the load. If I were to throw in a 100-ohm resistor after L3 (but before R4 and C8), would that help things?If not, what else can I do?If you're curious here is my setup.Here's the power supply. Some parts I only had available in SMD, so they are hidden underneath the board. Namely the 1uH inductor and 10nF 250V cap. The blue tape on the MOSFET was just so I could more accurately measure its temperature with my fun laser thermometer thing.Thank you!(Modified to add attachments)

author: StillTrying
author_rank: Super Contributor
timestamp: September 12, 2021, 12:34:23 pm
content: Some of that noise might be the scope probe ringing, there's always going to be some spikes, try carefully probing something such as the +12V with the small GND spring rather than the long GND clip.You should try to keep the high spikey current paths as short as possible, especially the 3 GNDs in green for minimum EMI.

author: WattsThat
author_rank: Frequent Contributor
timestamp: September 12, 2021, 01:14:08 pm
content: Your wiring/prototyping practices and the resulting current loops are the issue.Job one would be to provide a proper single, star grounding point for your 12v supply. As shown, the 170 volt boost converter is connected through a piece of #22 wire that has both the supply and return ground paths in it. But, what’s worse is that you’re connecting that ground point through a solderless breadboard back to the supply.You simply cannot do that with switch mode converters, the current paths must have the shortest, lowest impedance paths possible and a solderless breadboard cannot even get close to what is required to prevent the rapid changes in current in the switched inductor from becoming the rapid changes in voltage that you’re seeing on your scope.

author: Terry Bites
author_rank: Super Contributor
timestamp: September 12, 2021, 03:20:56 pm
content: Quote from: WattsThat on September 12, 2021, 01:14:08 pmA star point for the V+ supplies also matters just as much as the gnd star. Use separate input supply lines for the DC-DC conveter and the linear regulator. You dont want the LV Gnd having any DC-DC converter ground current flowing in it. The same applies for V+, You dont want any V+ current going into the DC-DC converter flowing in the linear regulator supply.A good PCB layout can make all the difference. Lose Q2 altogether (you could inhibit Q4 instead).Tie to supply paths or lines at C3 only. Increase C3 and use a low ESR type. I'd put a ceramic in parallel with C3. You can tighten the current loop at the input of the DC-DC converter with a common mode choke.Here are some handy tipsRead the free ReCom ebook: "DC/DC Book Of Knowledge".4.7K is fine BTW.

author: Mighty Burger
author_rank: Regular Contributor
timestamp: September 12, 2021, 09:03:29 pm
content: Hey guys, I appreciate the advice!Did some experimentation this morning. I did as StillTrying suggested and measured using the little GND spring on my probe, and the amplitude of the spikes were indeed smaller, but they didn't go away entirely.I then put the ground clip back on and clipped it to the probe to make a loop, and held it above the supply. Here's what that looked like:https://youtu.be/N7FNFoCtQA0I don't know much about antennas but it seems like I made a pretty decent radiator, oops! The scope is set to 200mV pk-pk, and I believe it has a 1MΩ input impedance.Now, I'm getting a little confused regarding this star grounding thing. I'm not really sure what that would look like in practice. I quickly drew up a couple very general sketches of what Ithinkyou guys might be talking about. Let me know what you think. (I plan on laying this out on a 2-layer PCB).Idea #1, where I still use large GND planes, but split the plane and have each plane connected to a common point right at the input capacitor:Idea #2, where I don't really have planes for the SMPS and just kinda snake everything together like this:Is this what you guys are thinking of?I'm not sure if there will be complications routing signals to the Board-to-Board connector. Somehow I'd need to get that 170V output to the connector.Elsewhere I've heard advice that it is good to have a continuous, uninterrupted GND plane, and this seems to conflict with the star-ground idea. I'm not sure how to make sense of all this

author: CaptDon
author_rank: Super Contributor
timestamp: September 12, 2021, 09:09:02 pm
content: If that project was on a proper PCB your problems would vanish. Even the ground leads of the scope will pickup noise in a kludge like you have there. I think your problems are already solved. Just get that mess onto aPCB with traces done in proper fashion and it will be fine.

author: Mighty Burger
author_rank: Regular Contributor
timestamp: September 12, 2021, 09:22:25 pm
content: Quote from: CaptDon on September 12, 2021, 09:09:02 pmThat's relieving to hear for sure!Now, the majority of this kludge you see in the pictures is the pile of alligator wires I have going to my nixie tube, since I couldn't really just plug the nixie into my breadboard.All of the SMPS is soldered onto a protoboard, so I don't think that particular section of the circuit is too messy, but it certainly isn't perfect. And like others said here it probably isn't connected to the rest of the circuit in the best way. I'm still hoping the issue is it's just messy like you said, because that means the problem will go away once I solder up a properly routed PCB.I'll have to get your guys's opinions once I get around to laying out the PCB before I buy the boards!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 13, 2021, 04:17:46 am
content: Huh, unrelated but R4 should be more like 100R, to dampen the network as shown (sqrt(L3/C8) = 100R).Also, what the heck is C5 doing there? Surely it belongs on the other side of R2?And what the hell is up with J2 vs. J? ? They're not even the samesize, let alone pinout!?I guess these are just representative, then? As it's all breadboarded right now anyway.Anyways, your measurement is most likely common mode: you'll see the same thing with the probe grounded to clip, and poking that at circuit ground. This means high-frequency currents are leaving the circuit somewhere (to surroundings, via power cable, etc.), and the reaction of that current makes the circuit ground voltage bounce, and hence also everything in the circuit, including supplies that are supposed to be quiet.I wouldn't be surprised if the culprit is the loop in the supply leads, loosely draped around the converter which has no ground plane, hence radiates nice high voltages in those tens of nanoseconds, transforming them into the, a couple volts at the leads or something like that.That you've built the converter on its own board, gives a straightforward solution: put it in a box (say of sheetmetal, or copper clad PCB), and where the wires pass through, either ground them directly (just GND), or add an LC between board and box (L towards the inside, C close to where the wire exits the hole). The metal shielding blocks the high frequency fields, absorbing or reflecting it so it stays inside; the wires would be prone to bringing it outside, hence they get filtered exactly where they exit, leaving no noise exposed.I've got several projects with a converter assembled in such a way, powering radio equipment. Indeed, with good layout, on a PCB by itself, you can get fair noise performance (sub mV), but to do better, shielding is an absolute requirement! And with a crap layout, you can do at least as well, with shielding and filtering. It's a highly effective method indeed.Tim

author: Mighty Burger
author_rank: Regular Contributor
timestamp: September 13, 2021, 04:59:30 am
content: QuoteHaha yeah, my bad. I updated the connector on the bottom board and forgot to update the one on the top to match, that's all. Looks like I forgot to add some component references on the top board too.QuoteI'll have to change that! Would that just help the network stop ringing faster?QuoteNot sure, I more-or-less used this design from ThreeNeurons:https://threeneurons.wordpress.com/nixie-power-supply/hv-supply-kit/On that page, he claims the purpose of R2 is really just some rudimentary protection against overcurrent. Would moving C5 to the left of R2 like you said improve performance?QuoteI'll have to experiment with my setup this weekend!I was considering adding a shield on the PCB to surround the supply but I thought it might be overkill. Something I could find here probably.https://www.digikey.com/en/products/filter/rf-shields/867Sounds like it might not actually be unreasonable to add one of these after all! (Though I think if I could get sub-mV noise with just a PCB layout alone, I'm OK with that.)You mention adding LC filters right inside the shield at the input/output. Just to check I'm understanding, L1 and C4, and L3, R4 and C8 would serve that purpose right?Are there any special considerations I might not be aware of when using a shield like this? Would holes in the shield, or the thickness of the shield walls, have any influence?I really appreciate your advice! You've been of immense help throughout my nixie projects and you've taught me a lot. Thank you!Jordan

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 13, 2021, 06:11:08 am
content: Quote from: Mighty Burger on September 13, 2021, 04:59:30 amYes. It probably won't ring all that much, as the load is quite small (a few mA; into a resonant tank of Zo = 100R, that's a few 100 mV peak), or may not be excited at all, as the optos are rather slow (oh, which if you're doing a multiplex scan, beware of that, it'll have to be quite slow; but with drivers everywhere, I don't think that applies).For RF filtering purposes, it would do to put a 3.3nF in parallel, right across the output; the R+C then dampens it. Or increase the values proportionally (e.g. 10 and 33nF), and reduce the resistor slightly (~68R?).QuoteMemes aside, MC34063 is at least a rudimentary current limiting device. It's NOT current mode, as it doesn't cease switching under overload conditions -- it's quite happy to destroy itself in that case. But putting C5 there, delays this action, so that -- Idunno, it's a stupid enough chip that I've never gotten any to play with -- not sure, maybe it doesn't really matter. If nothing else, itlookswrong to have way more capacitance inside of R2 and L1, than outside!For which, C3 should probably be 220uF. C4 and C5 maybe shouldn't be too big, on account of the MOS switch supplying them -- it has to dissipate full charging energy when turning on. And C4 doesn't matter so much, with Q2 being a ~short circuit when on; though it does help with L2 being there, wouldn't want Q2 to get zapped by flyback at turn-off. So, the caps being where they are, aside from C5 which should move to C7, isn't bad, just adjusting their values may be helpful.QuoteYes, though a single stage may not have all that much attenuation; or you might want low impedance caps in there (see the parallel C and R+C above). It'll certainly help with the RFI splats.Note that the reference board is tight, compact, and I think ground plane on one side? Plane serves as a shield, in the midst of the circuit itself; it's exposed on one or both sides, hardly an enclosure -- it can't block magnetic or electric fields around components, but it significantly cuts down on the paths between components, at least. Between that, and having all the connections off to one side, it probably doesn't make all that much noise -- still plenty that you'd see it on the scope with an inductive loop probe nearby, and maybe enough to hear it on a nearby radio, but certainly not the volts measured from your breadboard.QuoteYes! Holes let fields through, in proportion to their size, more or less. This is most pronounced at high frequencies (where the hole size is a substantial fraction of a wavelength), but still true at low frequencies (asymptotic LF response -- below say 1/20th wavelength, it's pretty much the same whatever dB/dec. slope down to DC).Holes aren't at all a non-starter: consider a 5-sided box, that's very long, one end open, the other end has circuitry. Fields from the circuit, terminate on nearby walls -- the long box is a below-cutoff waveguide. There are certainly frequencies where that box emits like a garden hose, but they're likely in the GHz (or 100s MHz for something on the scale of ductwork). And again, being below cutoff, asymptotic rules apply (fields drop off exponentially with length), it's just a matter of having a long enough, narrow enough opening that nothing of note comes through.In particular, since we're mostly worried about magnetic interference around switchers, the fact that magnetic field lines can't extend very far out of a box, is of great help here. If you made a net-size box (not one with high aspect ratio), and leave one side open, you'll get some noise in proximity to that opening, but it drops off quickly with distance and you can simply keep stuff away from that.The general truth is topological. Start with a closed metal box, poke a hole in it and run a wire through. Now you have coupling between the interior and exterior fields. Put a cap on it, and you short out the high frequency currents. You can continue enlarging the hole -- while keeping the wire(s) bypassed to an edge of that hole -- and only a modest amount of field leaks out, assuming everything is below cutoff of course. (Because again, if you're doing this in the GHz, at a certain size, holes will start transmitting very well; dimensions need to be kept small relative to wavelength, to maintain good shielding.)You can continue until the hole spans an entire face of the cube, and so on down the sides until you get a squat tray looking thing. This is a continuous process, and nothing fundamental has changed, merely a gradual increase in exposure of "interior" fields. Which again, if they don't extend very far to begin with, this need not be a problem.But let us do take stock of what the situation looks like now: with a PCB hovering over a panel, with shallow sides up around it, it's looking more like a ground plane with circuitry above it; perhaps rather far above it, whatever the standoff height is. We can shorten the field lengths by bringing that in closer. We can bring it all the way in until it's integrated with the PCB itself -- now we have a complete solid backside ground plane, circuitry on top, and shallow sides. Let's say we splay the sides out, so there's more just a rim of ground plane around a central circuit.And so that's what most PCBs look like, electromagnetically speaking. A bunch of circuitry, tight to a ground plane, with the ground plane dominating the overall aspect of the board -- that is, pretty much anywhere you go around the board, you're more likely to find ground, than any other node. Components and traces are visibly exposed, so they do couple with radiating fields -- they're potentially prone to ESD, RFI, and emissions. So your work is cut out for you, to some extent; you need a responsible layout. But the coupling isn't usually so bad that such a build fails tests. Hence, all the millions of electronics we have, that's little more than a PCB in a plastic box. You get no shielding from that! (In extreme cases, the plastic is metallized inside, and then guess what we have, topologically speaking?)Further reduction of the ground/shield, is not really practical. If we reduce it below the outline of components and routed traces, their fields become completely exposed, and it's a free-for-all as far as what dipoles couple where. Electrical performance is degraded, in part due to self-inductance (plain stray inductance is higher) as well as mutual inductance (coupling between parts of the circuit -- in your case, the switching loop on the converter board, coupling into the power leads / probes).This is why ground plane is the minimum / basic / default layout method. It's very effective, for the majority of cases.A few places you might avoid ground plane, are where you simply have no choice, due to cost, or high voltages; or where the stray capacitance dominates: that is, when we route a trace over plane, we get a transmission line, the impedance of which is determined by the geometry of the cross section (trace width, height over plane, dielectric constant, etc.) If we need a high impedance (that is to say, lower capacitance and higher inductance), we might remove the ground around those traces. We do incur higher coupling to nearby traces, so basically the whole layout needs to become looser as a result; this can be effective for high impedance, high voltage circuits, like tube amplifiers and electrometers.Note that high voltages, very easily demand very high impedances: a 100W converter at 100V, simply needs ~100 ohms, a very familiar trace impedance; a 100W converter at 10kV, delivers 10mA into a 1Meg load -- an impossible impedance to realize, at any kind of bandwidth -- hence such circuits being exclusively DC or resonant in nature! A corollary is, it's very difficult to get something high voltage, that's also limited in a familiar way as at lower voltages. Like a CC/CV supply, at low voltages you can make one that acts quickly (within microseconds, or a lot less if you really want to); at high voltages, even if your electronics are doing the job, the sheer fact that you have a wire (of some ~pF) charged to 10kV, automatically necessitates a short-circuit peak current of some hundreds of amperes -- if only for the nanoseconds it takes that wire to discharge. This manifests in all sorts of high voltage phenomena, like with static cling, the sound of a multitude of minute sparks jumping across a charged insulator -- each tiny spark has a peak current of some, probably fractional amperes in that size (i.e. the discharge of some ~cm of area), emitting noise up to some GHz I'd suppose. It's no accident that, despite the soft gooey flesh-body it's delivered from, ESD (human body model (HBM)) delivers peak currents of 10s of A, albeit for just 10s of ns.And conversely at low impedances, where inductance dominates, even for very shallow conductor-ground plane spacing, and wide conductor widths.Ah, but I digress; I love EM, I just wish it were easier to teach / understand sometimes...Tim

author: Psi
author_rank: Super Contributor
timestamp: September 13, 2021, 06:19:01 am
content: As others have said, having all those wires everywhere in a large assembly will give you an unrealistic impression that the EMI is bad.It's annoying, but usually the best option is to design the proper PCB and then test again once the circuit is in its final small size.Then, if needed, do a PCB v2 with some extra caps/inductors etcYou can even add PCB footprints for some extra filtering parts to the V1 PCB. If they don't end up being needed it doesn't matter, didn't cost anything to add them.

author: Mighty Burger
author_rank: Regular Contributor
timestamp: September 14, 2021, 03:53:40 am
content: Quote from: T3sl4co1l on September 13, 2021, 06:11:08 amThanks for the warning. The switching speed was something I was concerned about the optoisolators. I'm not planning on doing any multiplexing, however I do plan on doing some PWM on them for brightness control (by toggling the Output Enable pin of the rightmost shift register). I think I read somewhere that Nixies respond best somewhere in the multiple hundreds of Hz range, < 1KHz (don't quote me on that), and I believe that's what I'm running them at right now, so nice and low frequency.I did test them and I seem to be able to control the brightness fine, and the opto doesn't heat up.QuoteDone, done and done! See the updated schematic.Now I do have a concern about having the large 220uF capacitor as C3. The inductor L2 seems to need a lot of current when the power supply switches, and if C5 isn't able to deliver enough current, we have to go backwards through the chain through R2, L1, outside the shield,and through Q2before C3 is finally able to supply that current.While we gain in not having to charge up a 220uF capacitor through Q2 on startup, we'd lose in that (I think) current would have to be pulled through Q2 every time the SMPS switches. It also seems like I'd run into the problem of high-current spikes occurring outside of the shielded area, increasing EMI.Am I correct to be concerned about these things?Another user suggested ditching Q2, instead inhibiting Q4. However that would probably require a resistor to be put around the gate of Q4, which could start slowing things down and causing inefficiency. A big thing ThreeNeuron's emphasized with his design was that Q4 should switch as quickly as possible to maximize efficiency. I'd also probably have to add filtering to the signal going inside the shield which is not optimal. I might stick to using Q2 if possible.I wonder if I should add some sort of flyback protection for Q2, now that you mention it.QuoteThis was fascinating to read! I wasn't left with any questions to pick your brain with sadly, rest assured I didn't skip over it though!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 14, 2021, 07:42:34 am
content: Yeah, there's a compromise between cap value and transistor rating.Hmm, that thing can sink a lot of current, can't it. 12A peak, but looks like it would draw tons more if forced to (which wouldn't be very repeatable then!).It might be nice... hmm, adding a divider resistor between Q2 and Q3, another 22k say, so V(12V) - Vg(on) is only about 6V, and then add a small source resistor (12V to Q2-S) to limit current. Which would be what, 12A at a few volts, so 0.25 ohm would be in the right ballpark. Oh hey, already have one of those in the circuit too. This has the effect of reducing Vgs(on) when high currents are drawn, and reducing current acts to slow the charging of C5 (C5 would be the likely candidate for increasing the value of), reducing the peak temperature in the transistor.Alternately, if you have the exact part number for C3 we can look up its ESR and see if that serves as limiting. ESR over 0.5 ohm should be safe in regards to peak current, at least.And if we're adding a series resistor for a current limiting function, we might as well leave it by itself, putting it in series with the drain instead.External ESR is preferable, as dissipating the power in the transistor itself is likely fatal. Let's see. If it does 12A into 220uF (as a likely example), it takes (220uF)(12V)/(12A) = 220us to charge; or for a 1 ohm loop resistance (and both 220uF's acting in series), around the same for >90% charge (as RC exponential rather than constant-current ramp). That's (12V)(12A) = 144W initial, dropping to zero at the end of the pulse, say 72W average for 220us; the transient thermal plot (top p.5,https://www.vishay.com/docs/68768/si2307cds.pdf) shows 0.012 times, and RthJA is 166°C/W so 2 C/W, *72W is 144C temp rise, which... might just barely pass if it's sitting in a freezer? It's surprisingly close, and ESR would probably cover the difference. But just as well, ESR can drop the bulk of the voltage, significantly reducing the transistor's own dissipation.If it's able to switch fully, and C3(ESR) is very small, then a load ESR of 1 ohm is required, and peak power is around 12W. For an 80°C temp rise, a normalized transient thermal impedance of 0.04 is needed, or about 4ms pulse width. That implies load capacitance of about 4000uF, so the margin should be quite wide in this case -- and again, that assumes C3 is very much larger in value, and smaller in ESR, than the load.So, making C3 and C5 as 220uF and ESR > 0.5 ohm, should be perfectly fine, without any other changes.C4 should be fine to dampen L1. I wouldn't worry about C17 and C18, and C1 covers anything that might be needed on that node, as far as high frequency bypass, which really isn't anything besides the regulator itself so there you go. Which is happy enough with electrolytic supply too, so you could remove all the little caps on that side, really. (Leave C7 in. A larger value might even be desirable?)Oh, might be nice to add 4.7k from Q3-B to GND, just to make sure it stays off. It'll be kinda sensitive otherwise, like, if you're handling the circuit while it's powered up, and your fingers happen to touch 5 or 12V and Q2-B at the same time, it'll turn on, making other things much more...lively?I'd also make D3 more like 9 or 12V, simply because it doesn't need more; it's not that 15V is unsafe (the limit is 20V). Just a preference.Tim

author: Mighty Burger
author_rank: Regular Contributor
timestamp: September 15, 2021, 05:05:41 am
content: I wish I could be testing this as I go along, sadly time does not permit as college is in session. Maybe if I have time this weekend I'll test it!Quote from: T3sl4co1l on September 14, 2021, 07:42:34 amThank you for laying out your thought process, it really helps!I haven't found any part numbers yet. I probably need to get on that soon. I think I'm going to have to find some low-profile versions of these caps since I plan on having the power supply in the space between the two boards.In fact it might help if I elaborate on that. Here's a brief idea of how I'm imaging the assembly will look, minus the wood enclosure. I'll try to fit all the components on one side of each board (except for the nixies, which will be on the opposite side of the top board). Should help ease good PCB design and assembly I think. I'm currently thinking that I can mount both boards to a sturdy brass plate through standoffs (maybe with a little blue threadlocker). Then I could screw that brass plate into the wooden enclosure, which I'm now planning on routing out of a solid block of oak. Last time around I was asking about ways I could hack together an acceptable-looking clock, but I've since come to realize the college I'm attending has a "maker lab" and metalworking shop with a CNC router, metal lathe, and other handy tools for students to use, even for personal projects! So I can start to get a little more creative with the mechanical design. And I think this way it's more repeatable if I do end up selling a clock or two.I'm still debating on whether to have the buttons and barrel jack power inlet mounted to the PCB, or bolted to a second metal panel.Back to the capacitors and Q2. I didn't realize we were already in the red for Q2! Thank you for catching that!I'm considering still adding the 1-ohm resistor in addition to ensuring C3 and C5 have high ESR, just to sleep easy. Eh.. it's probably not necessary.Should I also aim for a higher ESR for C4? It's capacitance is only about an order of magnitude less than C3 and C5.QuoteDone!Although I did keep C1 next to the 5V regulator. (I actually made a note to myself a while back to update from the LM7805 since it looks like it's marked as obsolete in DigiKey, the LM340x-5.0 seems like a suitable replacement, I think I actually tested on the breadboard with this one.)The datasheet seems to recommend C1 especially if it's far from the power supply filter. I don't think it should really be far away though if I can lay the PCB out reasonably, but I think I'd feel a little more comfortable with that there anyways.I bumped C7 up to 0.22uF to match with C1, not really much of a change but it's better than nothing.QuoteHehe good catch, thank you! I guess it doesn't take much current on that base to get things going.QuoteAlright! I set it to 9V. Should give a little more time to start conducting in the case of transients, probablyWith all the changes made here's the updated schematic!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 15, 2021, 09:16:23 am
content: Whaddya mean? I see thousands of second sources: MC, L, UA, AS, SCD, etc. Nothing special about the LM version of 7805.C4 will likely have a higher ESR, on account of its smaller size. You'd have to go out of your way, like choosing aluminum polymer, to have it lower, and it still won't be a problem thanks to C5's ESR.That should look great when finished.Tim

author: Mighty Burger
author_rank: Regular Contributor
timestamp: September 16, 2021, 03:04:11 am
content: Quote from: T3sl4co1l on September 15, 2021, 09:16:23 amOh, good to know! I'm still trying to get a hold of what the different bits of part numbers mean. I don't think I've cracked the code yet. Do those prefixes refer to different manufacturers?QuoteThank you, I hope it does!! I owe you a lot of thanks for helping this come to fruition. Maybe if I end up making a few to sell I could come up with one extra clock to send your way.I'm hoping to get this PCB design out of the way soon but classes take priority sadly.I'm thinking a little more about my buttons and barrel jack. I have a couple ideas of what I could do.I found this image stored on my computer, I'm not sure where I grabbed it but I did a while back because I absolutely love the look of this style.I really like how they have metallic pushbuttons / barrel jack, and some labels imprinted on the plate. I was thinking I could do something very similar, maybe also have some basic instructions to make the clock more user-friendly. Lots of clocks I've seen online just have two or three puzzle buttons, and you have to unfold the paper manual to figure out how to operate it.The makershop at my university has one of those computer-controlled laser machines that can cut thin wood. I took a look at their training and they have a list of accepted materials. The only metal they will let into that machine is anodized aluminum, but that would probably work fine for etching text onto a plate. I'll have to email them and ask for more details.I'm having trouble finding buttons on Digi-Key. Thankfully the barrel jack wasn't an issue, I found this part in all of about 30 seconds:https://www.digikey.com/en/products/detail/tensility-international-corp/54-00064/6206245The buttons, on the other hand, there does not seem to be very many options. I've looked for a while, and I'm really having trouble finding any switches that are suitable. Any suggestions are much appreciated!I'll probably use JST connectors to connect the buttons and barrel jack to the bottom PCB.Things are starting to come together!