What if 10nF is cut in this circuit?  - Page 1
Forum section: electronics / beginners

author: bonyz
author_rank: Contributor
timestamp: August 12, 2023, 01:27:54 am
content: I couldn't enter the inductor data in LTspice so couldn't simulate it.Why is there 3 parallel capacitors in the left? What if say the 10nF is cut? I indeed destroy the 10nF when I tried to desolder the neighboring 0603 component and wonder how it would affect it. It is part of audio component.The circuit is connected to 5 Volts USB at left. Is the VCCA the output or the input? What does it do? Thank you!

author: ataradov
author_rank: Super Contributor
timestamp: August 12, 2023, 02:02:04 am
content: Absolutely nothing will happen. 10 nF here would realistically do absolutely nothing anyway.

author: themadhippy
author_rank: Super Contributor
timestamp: August 12, 2023, 02:15:02 am
content: QuoteYouve evicted sevral magical audio pixies so the audio quality is bound to be degraded

author: xrunner
author_rank: Super Contributor
timestamp: August 12, 2023, 02:19:48 am
content: Quote from: bonyz on August 12, 2023, 01:27:54 amIt's obvious - because they wanted 10.11 uF.

author: bonyz
author_rank: Contributor
timestamp: August 12, 2023, 02:28:45 am
content: Quote from: ataradov on August 12, 2023, 02:02:04 amWhat does circuit like this usually do? is the VCCA on top left the output or input? If output, what does the 5V do to it? It makes the 5V more stable or noisefree?If the 10nf has no purpose, why would they put it there??

author: ataradov
author_rank: Super Contributor
timestamp: August 12, 2023, 02:47:00 am
content: Quote from: bonyz on August 12, 2023, 02:28:45 amFilters the power supply. VCCA indicates that it is an analog supply, so extra filtering may be justified.Quote from: bonyz on August 12, 2023, 02:28:45 amCargo cult of capacitor placement. There are all sorts of ideal simulations that says that placing capacitors with decade values improves noise rejection. In practice with real capacitors it rarely does anything.To be fair, if I were doing a schematic for something mildly analog and possibly sensitive, I'd also place extra components just to have placeholders on the board for future tuning if needed. But in all likelihood removing that specific capacitor will not affect operation of the circuit.

author: golden_labels
author_rank: Super Contributor
timestamp: August 12, 2023, 03:10:53 am
content: It is nice, that they place a 10 nF capacitor next to one with 10 nF tolerance. Then put both of them, very precisely specified, beside a jellybean cap with tolerance likely in 2000 nF range.And yes, I am aware of the possibility of making an attempt to improve response. Just it being coupled with that extremely precisely defined inductor and mixing very different levels of details makes me cringe and give me the vibes already mentioned above.

author: WimWalther
author_rank: Regular Contributor
timestamp: August 12, 2023, 03:20:21 am
content: The small caps are present to bypass noise off of the Zener. FYI, zener noise is a sort of white noise hiss.In tube circuits where zeners are used to fix grid voltages (equivalent to the base or gate of a transistor), we would commonly use a single polyester 470nF or 1uF for noise bypass.We played around with decade values and pi filters, but couldn't see any improvement.

author: amyk
author_rank: Super Contributor
timestamp: August 12, 2023, 03:21:41 am
content: I suspect some things like this might be to make it easier to find if someone copied your design.

author: fourfathom
author_rank: Super Contributor
timestamp: August 12, 2023, 03:54:16 am
content: Back in the Olden Times, capacitors usually had wire leads, and thus significant lead inductance and low self-resonant frequencies. Also, the larger-value capacitors had greater series resistance than the smaller-value ones. This made some designs benefit from paralleling large and small capacitors. This was more important at RF frequencies than audio, usually.Now, with multilayer surface mount caps the series inductance, SRF, and ESR are often so good that they can safely be ignored. Circuit requirements differ, but the caps are much better than they used to be.

author: bonyz
author_rank: Contributor
timestamp: August 12, 2023, 04:29:02 am
content: The input is 5V DC from computer USB port. Does VCCA still output 5V DC? So the capacitors are used only if your laptop or computer is connected to AC adaptor? And the capacitors not necessary if laptop connected on battery?It will only take a minute to enter this in LTSpice. I dont know how. Kindly somone this weekend enter it and upload the LTspice file here so we can see the output in all its glory. Thanks in advanced!

author: ataradov
author_rank: Super Contributor
timestamp: August 12, 2023, 04:45:49 am
content: Can you show full schematic? Is there a chance that "5V" is not always 5V and may be higher? If it is always 5V, then with 6.2 V Zener the output would be 5 V minus some loss on other components.I'm not following your logic about AC adapter. The capacitors are needed for any power source, just not that specific precise combination. Missing one will not do anything bad.How do you know it will take a minute if you don't know how? What do you expect to see there? LTSpice would provide ideal components and voltage sources, in order to check how the circuit behaves you need to manually add expected imperfections. And you obviously don't know that.And what is your final goal here?

author: Konkedout
author_rank: Frequent Contributor
timestamp: August 12, 2023, 05:01:01 am
content: Realistically, the 10 nF will not do much. But in theory, smaller capacitors have less stray series inductance (assuming they are in smaller packages and placed more tightly on the PCB so do a better job of bypassing high frequencies. But these days you can get 1 uF in an 0402 and I hate to work with anything smaller than an 0603.

author: Bud
author_rank: Super Contributor
timestamp: August 12, 2023, 05:17:33 am
content: Quote from: WimWalther on August 12, 2023, 03:20:21 amYou need to use a spectrum analyzer to "see" improvement. An improvement is going to be at -50...-60dBm level, you can't detect such levels with you ears.For audio frequencies it will not do anything in terms of listening experience but for specific power supplies it may help supress oscillation.

author: bonyz
author_rank: Contributor
timestamp: August 12, 2023, 06:34:18 am
content: It is part of the Arduino (see image below)...The input can either be 3.3V or 5V. What is the purpose of the inductor and zener? If the 5V is pure 5V DC, then no purpose for them? Or could the purpose be to clean the 5V DC that could be somehow messed up by the Arduino crystal?

author: ataradov
author_rank: Super Contributor
timestamp: August 12, 2023, 06:48:28 am
content: You are really overthinking it.The diode is there for a basic protection against over-voltage, it normally does nothing. Inductor may help with noise rejection, but realistically does nothing useful. And the capacitors are there because Arduino is over-engineered for no reason.It is not like Arduino board needs high analog performance. It samples potentiometers most of the time, if that.Also, what Arduino board is this? I don't remember classical U3 board having anything like that. If this is some special analog-oriented version, some of that stuff may make more sense.But you still have not answered the question - is missing capacitor your only concern? If so, this is a huge waste of time, it does nothing, forget about it.

author: bonyz
author_rank: Contributor
timestamp: August 12, 2023, 06:58:56 am
content: Quote from: ataradov on August 12, 2023, 06:48:28 amBut the diode, inductor and capacitors are not powering up the Arduino. But the opposite, that is, the Arduino is powering up those parts to create VCCA. Is it not? And the VCCA is powering up the circuit below to produce V_REF. Correct? Or did you mean VCCA is the input and powering up the diode, inductor and capacitors which are powering up the Arduino??

author: ataradov
author_rank: Super Contributor
timestamp: August 12, 2023, 07:06:06 am
content: This connector is designed to provide external power. Obviously if VCCA is powered by some other source, then it would appear on the connector (assuming jumper is installed), but the selection 3.3V/5V won't make sense.VCCA is internal power rail for the whole board, it can be powered by many sources. It can be provided though that connector, it may be provided by USB or whatever else is on the board.VCCA powers the reference stuff.Again, it is hard to comment without looking at a complete schematic. And you refuse to provide it.

author: bonyz
author_rank: Contributor
timestamp: August 12, 2023, 08:44:44 am
content: Quote from: ataradov on August 12, 2023, 06:48:28 amIt's an Arduino duo..https://learn.sparkfun.com/tutorials/arduino-comparison-guide/atmega328-boardsThe main Arduino board is connected to USB via USB type A to USB type B connector. So it's getting main power from computer. And the diode, inductor, capacitor on a separate board is getting power from the main Arduino connector and it is to produce clean VCCA to create VREF that will be used on a very sensitive instrumentation amplifier. We trying to copy a section so I'll share about it after my partner gave approval. This is to avoid competition.So if you will build a very low-noise sensitive instrumentation amplifier that needs VREF (powered by VCCA). You still won't need to be worried by that one missing 10nF capacitor? Or will it mess up the extremely low noise sensitive instrumentation amplifier?

author: Siwastaja
author_rank: Super Contributor
timestamp: August 12, 2023, 09:02:32 am
content: Likely nothing happens, but it could also start work better due to removal of a possible resonance generator circuit. The circuit is an excellent example of dangerous cargo cult engineering gone wrong.While at it, you can also remove the 100nF. The only reason to use such smaller values would be the fact they come in smaller packages and can be placed closer to where low-ESL capacitance is needed. But with the 10uF part already in 0805 package, I don't think you can significantly improve the layout. By removing C25 and C26, you would make some room to move C27 closer to the load.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 12, 2023, 12:51:13 pm
content: Avoid reading too much into superstition. Parallel capacitors of graded values are a direct example of superstition in engineering. There is some merit to the idea, but it's almost never executed correctly, and we can see from the types of associated components that it's utterly irrelevant to apply here.Despite electronics being an eminently scientific field, the fact remains that most engineers will never have the time (or interest, frankly) to test every element of every design. Some elements are calculated from reasonable design equations and related assumptions (and, occasionally, those assumptions are remembered correctly, and their applicability confirmed..), but many are also just left to straight up tradition -- or superstition.Consider: What bypass capacitor is default -- why 0.1uF? What pullup resistor is default -- why 10k? Probably because someone once said so; or one got the idea that, because these show up most commonly, there's something special about them. And so the meme reproduces, unchecked by critical analysis.(As it turns out, bypasses and pullups are usually of such value that, anything in a wide range will do. It would be nice to use maximum-value pull-ups to reduce current draw, or minimum-value bypasses to reduce component size/cost, but even these constraints are often so minor that they can be ignored, and default values chosen instead.)And by "interest", there, I mean not just the engineer's care to go and test something, even when the means and opportunity to do so are available (which often are not, due to budget or time constraints of a project); but even just the sheer idea that there is something here that *can* be tested, let alone *how* to test it.Case in point: to characterize bypass capacitors, we would ideally perform an impedance measurement with an RF bridge (typically the bridge comes as part of a vector network analyzer (VNA) instrument). Install the passive components on the board (leaving nearby chips off), wire a transmission line into the respective chip(s)'s power pins (this must be done carefully; for example a coax cable must be installed with shield widely bonded to ground plane first; assuming a ground plane design was used on the PCB in the first place -- and the whole exercise is a whole hell of a lot less representative, let alone meaningful, if not!), perform whatever open/short/terminated calibration is necessary given the test conditions (short can be done on-board by shorting the coax, but open might be done before soldering the cable down, or by lifting the signal connection off the board momentarily), and then run the test. A variety of tests and testing methods are possible just for the passive networks we use for power distribution, signal filtering and etc., let alone more complicated systems like device-level EMC, or software testing (beta testing, automated fuzzing, code analysis, etc...). (Software is more-or-less a subset of electronics these days, but offers a depth and breadth of complexity far different from ordinary electronics. Hence computer science (CS) being its own thing.)And who would ever think to test a bypass cap (or array thereof)? You almost never see it discussed. Even though having reasonably clean, low-impedance voltage supplies is the underpinning of all modern electronics; so, you'd think there would be some interest there, or pressure to verify it. But nah. In fact, assumptions underpin a disturbing amount of engineering; and, despite that, real work can get done, so, I mean -- it works. When it does, anyway.Tim

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 12, 2023, 01:00:15 pm
content: The capacitors are part of a decoupling circuit. All, and especially digital IC's need decoupling capactors because each wire and PCB track is slightly inductive and the current peaks drawn from the supply voltage can cause dips in the power supply voltage to an IC otherwise. The location of such capacitors is also quite critical. They must always be as close as possible to the IC they need to decouple. The value of such capacitors is not very critical. For 30+ years it was standard to have a 100nF capacitor for each pair of power pins on each IC (an that value was also pretty much randomly chosen), and that was good enough. In these modern times switching frequencies of digital IC's have increased to many hundredths of MHz, and even several GHz, and other problems started to turn up. The problem was that even a 100nF in for example an 0805 package has a tiny bit of parasitic self inductance, and at some frequency that inductance starts to dominate. Physically smaller capacitors such as 0402 have a smaller parasitic inductance, and thus keep capacitive at higher frequencies. This started about 20 years ago when clock frequencies became high enough for this effect to become an issue. Back then physically small capacitors with a high capacitance were not available, and thus it became common to use a 100nF capacitor and a smaller capacitor in parallel. These effects are also very hard to measure and verify in a laboratory, (measurement equipment that most people could afford was much less advanced then it is now, and even now it's difficult to measure reliable at 500MHz or higher frequencies. Just probing is difficult even if you have the right equipment). So most designers just trusted on application notes and when this got engraved in their brain as a rule, they just kept on using it forever.For old school technology such as an ATmega328 this is all quite over the top, and I agree with Siwastajas remark of "cargo cult engineering gone wrong".The electrolytic capacitor has a somewhat different but quite similar function. It is usually called a "buffer capacitor". and it works at lower fequencies. Normally it's use is to form a filter with the power supply cable to the PCB, to ensure a more steady DC current to the PCB as a whole. In this circuit, the power is probably first going to the digital part, and then via the inductor to the analog power supply pin. The high ESR of the electrolytic is probably supposed to detune the Q of the LC filter and dampen possible oscillations in the inductor.The parts are drawn close to each other (and far away from the IC) because they have a similar function and the designer of this schematic assumes that anyone reading the schematic is familiar with the use and placement constraints of these parts. Some designers have a practice to draw each and every decoupling capacitor close to the IC it is supposed to decouple on the schematic, but I find that practice counter productive. Most often there is not much place in that part of the schematic, and I find it distracting and it easily obfuscates other things happening right around an IC.I usually draw all the decoupling capacitors in parallel and put them in some corner of the schematic usually near the power supply section, because they are related to the power distribution.

author: wraper
author_rank: Unknown
timestamp: August 12, 2023, 01:05:21 pm
content: Quote from: WimWalther on August 12, 2023, 03:20:21 amThis zener is not even conducting here.

author: ataradov
author_rank: Super Contributor
timestamp: August 12, 2023, 03:49:45 pm
content: Quote from: bonyz on August 12, 2023, 08:44:44 amYour link contains no "Arduino duo". Can you link the exact schematic?Quote from: bonyz on August 12, 2023, 08:44:44 amOk, so this is schematic of your design, not Arduino? I'm confused.Quote from: bonyz on August 12, 2023, 08:44:44 amNo, it won't do anything. And "extremely low noise sensitive" is not a quantitative measurement. What is so "extreme" about it? If it is really so extreme, then depending on circumstances, powering things from USB may not be a good idea in a first place.

author: BeBuLamar
author_rank: Super Contributor
timestamp: August 12, 2023, 04:41:17 pm
content: What would be the difference between the 3 capacitors vs a single one of 10.11 MicroFarad?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 12, 2023, 05:52:10 pm
content: Quote from: BeBuLamar on August 12, 2023, 04:41:17 pmBasically you get an impedance more like this,rather than a single valley.If the peaks inbetween are well controlled (by judicious choice of capacitor ESR), the result can be better (lower impedance over a wider frequency range). If not (just stacking ceramics in parallel), the peaks can be quite high (several ohms), and that may have consequences for device performance.The difference between cargo cult and science is modeling and measurement.Tim

author: Siwastaja
author_rank: Super Contributor
timestamp: August 12, 2023, 06:00:01 pm
content: See this thread:https://www.eevblog.com/forum/projects/decoupling-caps-value/?allspecifically replies 23, 27 and 30

author: bonyz
author_rank: Contributor
timestamp: August 13, 2023, 01:32:19 am
content: Before when I tried to short the right side or use resistor of 0 Ohm (isn't it 0 Ohm is same sa short?), the 0603 C25 capacitor at middle got accidentally desoldered from the solder heat. I transferred the original C25 capacitor to between the left capacitors (shown in blue arrow from middle to left between C27 and C26 in original diagram, the controversial 3 parallel capacitors illustration you saw earlier)This occured because I had difficulty removing the remaining solders at the middle and I couldn't reinsert the C25 capacitor at original position. Also I'm not sure the C25 is still viable with all the heat hence this thread.Anyway. What new noises were introduced in the above solders and heating and how they occur?Also I know that at high frequencies. Impedances of capacitors got lowered and acting like short circuit that produces voltages of zero. In this case. It's decoupling capacitors. For value of 10uF. What kind of power line noises get filtered and at what frequencies? How do you compute for it?

author: bonyz
author_rank: Contributor
timestamp: August 13, 2023, 07:30:28 am
content: Here are clearer photos described in last message above.Original area (before alternation made).Following is alteration (C16 removed, R18 shorted to make it 0 Ohm, the procedure damaged C25 and I moved it between C27 and C26):The solder heat has deformed the area. Could it have destroyed the capacitors? Solder used.When soldering 0603 components. What kinds of solder are you supposed to do? And how do you desolder or flatten the rough solder splattered surface so capacitors or components can be replaced?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 13, 2023, 12:17:04 pm
content: Use a bigger tip and preheat the board to 100-150C. Use paste flux.Tim

author: xrunner
author_rank: Super Contributor
timestamp: August 13, 2023, 12:27:44 pm
content: Quote from: bonyz on August 13, 2023, 07:30:28 amJust removed and replaced some 0603 stuff recently. Add additional flux. Add more solder and use a chisel tip. Move the tip back and forth and the solder on both sides of the component will melt. Swipe off the component. Use desoldering braid to remove all the extra solder. Clean the area. Re-solder with new components (add more flux).Look at some of the very good SMD soldering videos here -https://www.youtube.com/@Androkavo

author: themadhippy
author_rank: Super Contributor
timestamp: August 13, 2023, 02:09:08 pm
content: Quote1 / (2 × π × f × C) were f is your frequency in hertz and c is your capacitance in farads,that'll roughly tell you the equivalent resistance of the cap at that frequency.

author: fourfathom
author_rank: Super Contributor
timestamp: August 13, 2023, 02:37:56 pm
content: You can sometimes find values in the datasheet for ESR and Self-Resonant Frequency. Lead/trace inductance will also affect the SRF. Of course it's even more complicated than the image above shows. Here's more:https://www.johansontechnology.com/srf-prf-for-rf-capacitorsTo unsolder small SMT parts I sometimes use two fine-tip soldering irons. Better though is a hot-air rework tool with a small nozzle and a pair of tweezers. Otherwise try the "back and forth heating large blobs of solder" method.

author: rstofer
author_rank: Super Contributor
timestamp: August 13, 2023, 07:10:59 pm
content: Dave did a video:That is some pretty poor soldering. Use more paste flux to help the solder wet the surfaces.You might try dabbing some solder paste (with flux) on the pads then placing the components. While holding the component in place with curved tweezers, hit the joint with the soldering tip.Wire solder works but it usually takes a dab of flux. In fact, put the flux down first and place the component in the puddle. Put a dab of solder on the iron tip and hit the joint. There's no need to use the wire solder directly on the component.

author: radiolistener
author_rank: Super Contributor
timestamp: August 13, 2023, 07:16:29 pm
content: Such capacitors are added to block RF noise at high frequency. Because high capacitance capacitors cannot block it due to high parasitic inductance.If you remove it it leads to a higher RF noise on power line. It may lead to unstable work of your circuit, or it can still work but will be more sensitive to RF environment and interference from nearby electronics, it depends on exact case.

author: bonyz
author_rank: Contributor
timestamp: August 13, 2023, 09:38:38 pm
content: Quote from: radiolistener on August 13, 2023, 07:16:29 pmWhat if the circuit is totally battery powered. Can RF from radio stations affect it if the 3 capacitors were removed? You mean radio stations or cellular phones can couple to the circuit pcb which acts like antenna?

author: fourfathom
author_rank: Super Contributor
timestamp: August 13, 2023, 10:16:55 pm
content: Quote from: bonyz on August 13, 2023, 09:38:38 pmYes, without a doubt. I can tell you horror stories about fixing susceptibility to RFI in battery-powered devices.

author: bonyz
author_rank: Contributor
timestamp: August 13, 2023, 11:31:13 pm
content: Quote from: fourfathom on August 13, 2023, 10:16:55 pmAre their faraday cage like enclosure for circuit? how does it look like? I imagine like a screen cage? Haven't seen one yet.Also if your op amp has bandwidth of only 2kHz for certain gain (like 100). Can RF noise of higher frequencies still affect it? How? maybe resonating the op amp internal parts?

author: wraper
author_rank: Unknown
timestamp: August 14, 2023, 02:04:53 am
content: Quote from: bonyz on August 13, 2023, 07:30:28 amWith such poor PCB layout adding smaller caps would not make any improvement even if it actually mattered.

author: WimWalther
author_rank: Regular Contributor
timestamp: August 14, 2023, 02:19:28 am
content: Quote from: fourfathom on August 12, 2023, 03:54:16 amMight be worth mentioning that leaded, spiral-wound caps are still the norm in point-to-point builds and circuits with high B+ voltages.. like tube audio gear. The well-regarded (...) Sprague "orange drop" parts being one nearly ubiquitous example, or the Illinois MPE / MPW series.

author: wraper
author_rank: Unknown
timestamp: August 14, 2023, 02:27:35 am
content: BTW this schematic is "genius" in many ways. Not only they decouple opamp power with 2 capacitors. They put 3 capacitors to the output of an opamp, two of them to GND (one 47uF tantallum, I wonder if they added this much capacitance because this garbage was oscillating), another to VCCA when there should be none at all. Then there is another 2 cap nonsense with C10, C12 connected to the same poor output of an opamp already abused by 3 another capacitors. Then they use 2 caps for AP431 instead of one for no good reason.Quote from: bonyz on August 12, 2023, 06:34:18 am

author: bonyz
author_rank: Contributor
timestamp: August 14, 2023, 04:35:41 am
content: Are there any generic circuit to create VREF that has fewest components and time tested that you can use as voltage reference to use in any instrumentation amps and op amps?Also what particular noises are introduced if you put all of them in breadboard, or buy separate modules (with separate functions) and connect them with a 6 inches pair of wire? What size and length of wire that can produce less distortions and what inductive and capacitive interferences that can be created in such short wires?

author: wraper
author_rank: Unknown
timestamp: August 14, 2023, 10:31:00 am
content: It's not that there are just too many components. Those capacitors do harm, not good. OPAMPs are not supposed to drive highly captative load (unless specially designed to do so), they misbehave when doing so. And adding capacitance from VREF to VCCA literally worsens performance as noise from VCCA can now freely pass into VREF.QuoteThe fewest components would be to use internal MCU VREF. Also it's not clear why 1.5V is needed. If 2.5V is OK, you could get it straight from AP431, which BTW is not that good of a reference, just cheap.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 14, 2023, 12:43:37 pm
content: If this is a for an ATmega family Arduino, external ref is desirable; the internal ref on those is rather a joke. XMEGA and up are passable though (more bits ADC too).There are '431 variants (TLV431, LMV431, ZR431L, etc...) with lower threshold voltage, also lower current consumption and lower noise are possible. '431 (in the tighter precision grades) is adequate for the basic ATmega ADC (10 bits, with hardly 8 of them guaranteed).Note that ADC performance is degraded below some minimum recommended Vref. Better to amplify small signals, than to reduce Vref. (Some gain is also possible, on some of these: XMEGA ADC has an iterated gain-of-2 feature for example.)Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 14, 2023, 12:51:14 pm
content: Quote from: WimWalther on August 14, 2023, 02:19:28 amNon sequitur -- almost all film caps are rolled, regardless of ESL. The most common differentiator is whether there's a connector tab (typical of canned oil types) or schoopage (everything else).In fact Orange Ddrops have quite good AC performance, but for the steel leads (see 716P instead), and the high cost (TDK, KEMET and others have cheaper parts of comparable ratings).Tim

author: wraper
author_rank: Unknown
timestamp: August 14, 2023, 01:42:14 pm
content: Quote from: T3sl4co1l on August 14, 2023, 12:51:14 pmI do not agree with that, many (especially small) film capacitors in plastic epoxy filled box are stacked, not rolled. Does not have much practical difference though as long as terminals are attached to metal sprayed ends of the stack/roll.

author: bonyz
author_rank: Contributor
timestamp: August 15, 2023, 11:22:17 pm
content: The VCCA and VREFs and all those circuit are powering up this EKG/EMG circuit:complete schematic:Now do all those capacitors justify it because it is powering the EKG/EMG?I didn't share it before because people got nervous about medical electronics and afraid the newbie may use it at hospital. But don't worry. I follow the warning note by Olimex by heart which is:"This evaluation board/kit is intended for use for engineering development, demonstration, or evaluation purposesonly and is not considered by OLIMEX to be a finished end-product fit for general consumer use. Personshandling the product must have electronics training and observe good engineering practice standards. As such,the goods being provided are not intended to be complete in terms of required design-, marketing-, and/ormanufacturing-related protective considerations, including product safety and environmental measures typicallyfound in end products that incorporate such semiconductor components or circuit boards."Where are you supposed to add the Isolator? It's connected to laptop usb and battery powered only anyway. Do you know of other schematic like it but medical grade? I'm just curious how it differs to $10,000 EMG. What chips are used in the latter?About the Electrode:"**The cable features three electrodes – two data electrodes (1 channel) and DLR electrode(feedback). If you use more than one SHIELD-EKG-EMG you can use cables without DLRfor every shield after the first."So VREF is connected to the right foot as part of DLR feedback. Are all the VCCA, VREF design justified? Or do you still consider them poor design?Again I don't use it as medical device so don't worry. Heck I don't even use it as ECG/EMG because after you try it once. You are tired of it. I'm just curious how it compares to $10,000 version. Is there such that uses superconductor as detector element?

author: wraper
author_rank: Unknown
timestamp: August 16, 2023, 12:13:47 am
content: Quote from: bonyz on August 15, 2023, 11:22:17 pmI see that V_REF actually a virtual ground, not voltage reference. Still it's a poor design which can only be explained by a poor knowledge of whoever designed that.Input ESD protection by PGS1/2 provides no actual protection. Why in hell anodes of D1/D2 pretection are connected to virtual ground and not actual ground? IC2B supposedly adjusts DC output voltage of in-amp equal to virtual ground, but what it's supposed to achieve compared to directly connecting REF input to virtual ground directly when there is C7 DC block anyway and offset voltage is pretty much irrelevant? (EDIT, Looked into INA321 datasheet and it looks like it's a result of a bastardization of ECG circuit found there) Neither I'm convinced it needs DC block capacitors at each amplification stage and as a side effect requiring DC bias resistors for inputs. Using X7R cap for active filter is questionable. IMHO you could easily throw out 50% of the parts from this circuit and make it work better at the same time.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 16, 2023, 01:47:33 am
content: Quote from: wraper on August 16, 2023, 12:13:47 amHow so? It's buffered (op-amp output), not virtual ground (op-amp input held at GND by action of feedback through a network).If the op-amp buffer were handled properly (damping resistor feeding bypass caps), and the capacitance increased a bit (I'd use one or two 1uF+ ceramic placed very near D1 and D2).Also if the input signal is very low, D1 and D2 could just be back-to-back tied with VREF. Instead of clamping positive to VCCA (which needs a local 1uF+ for the same reason).QuoteThis.Tim

author: CatalinaWOW
author_rank: Super Contributor
timestamp: August 16, 2023, 02:01:59 am
content: Tim comment and question about why the "standard' values for pullups and bypasses probably has a self fulfilling economic component. As production volumes of these components rise the cost goes down. Since a wide range of values work, pick the cheapest one.Paralleled filter capacitors largely come as Tim mentioned. Many beginners for time or capability reasons don't fully analyze every detail of their circuits. And once upon a time the app notes for many common linear ICs recommended exactly this configuration. The supply is often the least interesting part of the design so the app notes was copied and pasted in. Thus creating a tradition which is difficult to fight.

author: coppercone2
author_rank: Super Contributor
timestamp: August 16, 2023, 04:50:57 am
content: lol man get some soldering tweezers or whatever so you don't worry about destroying parts. It looks like a EMI precaution.But I find it hilarious that people are up in arms over like a 50 cent gamble/addon.. the sky is falling. the thread sounds like a broke ass company is doing a major product releasebut I guarantee you, the most important thing you can do is learn to solder that board without worrying about destroying parts, rather then trying to figure out what you can destroy...you can try heat sinks, heat shields, different tools and techniques in this circuit to actually get better at something

author: ataradov
author_rank: Super Contributor
timestamp: August 16, 2023, 04:58:55 am
content: I suspect this is the same OP that was obsessing over ADC in some 40 year old MCU. So, obsessing over things that don't matter is a theme here.

author: coppercone2
author_rank: Super Contributor
timestamp: August 16, 2023, 05:02:38 am
content: the rant about potentiometers being the end all for MCU is comedy gold.hi, sensors calling.

author: bonyz
author_rank: Contributor
timestamp: August 16, 2023, 05:26:22 am
content: I'm reading a lot about the Driven Right Leg (DRL) circuit and electrode. It is not just a simple ground. Somehow the common mode in the body can be inverted and feed back to the body via the DRL electrode. Which of the circuit in the diagram exactly does the Inverting and feeding back? Or maybe it uses some kind of short cut and nothing is inverted?Reference about the DRL I read at Quora"The reason this is needed is because the body acts like a radio antenna, producing signal variations much greater than the tiny impulses produced by the cardiac tissue. Unless these larger signals are filtered out, the ECG signal is lost in the noise.To counter this, the monitor circuit compares the raw signals from the other leads to determine what to filter out and what to pass on. The “noise” signal is then inverted and fed back to the skin via the right leg lead, canceling out the noise component. This turns the riot of noise from external sources into a stable, zero-voltage baseline."Also I readhttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC7219345/"According to the AAMI EC 11 standard, the maximum system noise allowed is 30 µVp-p for an ECG".Well ECG or EMG has milliVolt level waveforms only much like microphones (they are not EEG which uses 1 to 10 microVolt). So how can 30 microVolt noises affect 1mV to 10 mV waveforms?

author: bonyz
author_rank: Contributor
timestamp: August 16, 2023, 08:19:29 am
content: The following is when the right leg electrode was placed. The waveform noises at the end are due to my clicking the mouse to take the screen shotThe following is when the right leg electrode was removed.So the inverting circuit and feedback is fully working, or can simple grounding do the trick?Ok here is what I planned to do. I want to change the bandwidth of the module from 40 Hz to 20,000 Hz.Then I'll try to create capacitive coupling electric field that vary from 1 to 20,000 Hz that can couple with body (no contact) and see the waveform of the modified EMG conform to the capacitive coupling frequency.Then final test is by rapidly changing the capacitive coupling frequency, I can transmit music into the body and the circuit display it at the screen and maybe even playing back the music. Is this possible?Also how do you create capacitive coupling transmitter circuit that vary from 0 to 20,000 Hz and couple it to the body non-contact? Has this been done before?

author: wraper
author_rank: Unknown
timestamp: August 16, 2023, 10:51:41 am
content: Quote from: bonyz on August 16, 2023, 05:26:22 amNope, in this particular circuit it just feeds constant 1.5V.Simplified ECG circuit example in INA321 datasheet (page 14)https://www.ti.com/lit/ds/sbos168d/sbos168d.pdf?ts=1692145737378and this seems to be heavily bastardized version of that.

author: wraper
author_rank: Unknown
timestamp: August 16, 2023, 11:12:16 am
content: Quote from: T3sl4co1l on August 16, 2023, 01:47:33 amIt's buffered 1.5V used thorough of the circuit the same way as if it was GND in a split supply. IMHO it has all signs of the virtual ground.QuoteThere is 47uF to GND + a bunch of small caps to GND and VCCA. I meant more like it's not anADCreference. Virtual ground is still a reference point.

author: bonyz
author_rank: Contributor
timestamp: August 16, 2023, 04:22:10 pm
content: Here is what is so puzzling.The main purpose of right left drive is to improve the CMRR by filtering mainly powerline 60 Hz noise. The Olimex doesn't have any right leg drive but why does it eliminate powerline 60 completely when you put the right leg electrode (as shown in the output graphs a few message back?I read this part in physics stack exchange:https://electronics.stackexchange.com/questions/329476/what-does-this-op-amp-circuit-do-part-of-an-ecg"What the Driven Leg circuit does is use feedback techniques to measure the common mode voltage, and feed it back through the reference electrode. This effectively reduces the impedance of the connection at the reference electrode by a factor of the gain of the feedback.".Could the Olimex somehow able to pull the same trick, by maybe also effectively reduces the impedance of the connection at the reference electrode without using any feedback? Maybe the designer is really genius after all?