should I split nets into analog and digital? arduino controlled tone control - Page 1
Forum section: electronics / projects

author: dosensuppe
author_rank: Contributor
timestamp: April 08, 2025, 12:29:00 pm
content: Hey there.So I have been working on this arduino powered amplifier control for quite (too long) a while.What it does:- controls a bunch of MCP4251 digital pots to adjust a baxandall network- switches a bunch of relays, so multiple channels can be selected- has an IR remote control (not implemented yet) as well as buttons on the front panel- has a big LCD screen to display GUI with set values and a nice animation of an fft calculation (fft not implemented yet)I have only made the schematic so far since I'm a bit unsure about certain aspects of the design mainly:does it make sense to have the VCC and GND nets spilit into digital and signal lines?the layout is supposed to be double sided and will be almost entirely THT.are there some other faults I have been too blockheaded to notice?code and KiCAD schematic attached.looking forward to your suggestions.

author: dosensuppe
author_rank: Contributor
timestamp: April 10, 2025, 09:06:06 am
content: So to reiterate how would I best go about splitting the digital from the analog net?

author: eleguy
author_rank: Regular Contributor
timestamp: April 10, 2025, 09:40:22 am
content: Maybe one can get started from here (just as an example)"What do you call an Engineer who splits a Ground Plane? A Customer!" - James Pawson

author: dosensuppe
author_rank: Contributor
timestamp: April 10, 2025, 01:24:55 pm
content: Does it still make sense to have the VCC planes seperated with a choke?

author: PGPG
author_rank: Frequent Contributor
timestamp: April 10, 2025, 03:25:45 pm
content: Quote from: dosensuppe on April 10, 2025, 01:24:55 pmYour FL1 common-mode choke filters between +5VCC and the other both VCCs, but ensures that there is no filtering between +5SVCC and +5DVCC (it is how common mode choke works). So it will filter both your voltages against disturbances coming from external supply and filter generated in your circuit disturbances against going out from your device into its supply. But disturbances generated in your digital supply will be copied at your analog supply what is not what you probably want. Two separate chokes will be better here.Common mode chokes get high common mode inductance at small size thanks to cancelling current going in both coils (DC magnetic field is reduced to zero avoiding core saturation). Your connection does not ensure current in one coil being the same as in the second and flowing in opposite direction.

author: dosensuppe
author_rank: Contributor
timestamp: April 11, 2025, 10:06:45 am
content: I removed the +5DVCC net and now connect the digital parts directly to the main +5VCC net and seperated only the analog net from the main net with a choke like you suggested, so only one choke is needed. Also added a choke for the negative voltage.Completely dropped split GND.Will a 10mH choke like these suffice? (5pcs for 50ct!!)https://de.aliexpress.com/item/1005007929013486.html?spm=a2g0o.productlist.main.9.395295a9ygdZ0m&algo_pvid=0304e920-89b8-4b95-80fe-0db931b889d1&pdp_ext_f=%7B%22order%22%3A%2243%22%2C%22eval%22%3A%221%22%7D&utparam-url=scene%3Asearch%7Cquery_from%3AI also want to add a 47uF MLCC to the LM317/337 output, but read that this may lead to instability since the regulator requires a certain ESR. Would placing it after the choke (picrel) mitigate this problem?https://www.linkedin.com/pulse/problem-using-multi-layer-ceramic-capacitors-mlcc-output-pirhadi

author: dosensuppe
author_rank: Contributor
timestamp: April 14, 2025, 01:56:11 pm
content: fugg. I noticed I had it completely wrong. I would need to route the return current through the choke to have it cancel its differential or common mode noise. Meaning I would need a seperate GND. Am I getting this wrong? I just want to cancel out the noise coming from the digital line.https://www.coilcraft.com/en-us/edu/series/a-guide-to-understanding-common-mode-chokes/

author: Terry Bites
author_rank: Super Contributor
timestamp: April 15, 2025, 08:48:57 am
content: Read Dis!www.analog.com/en/resources/analog-dialogue/articles/what-are-the-basic-guidelines-for-layout-design-of-mixed-signal-pcbs.html

author: dosensuppe
author_rank: Contributor
timestamp: June 23, 2025, 09:56:38 am
content: I made a few changes to my board. Among them removing the symmetrical supply and adding a switching regulator for the digital electronics.Would it make sense to isolate the analog supplies with a choke like pic related to cancel out eventual noise coming from the switching regulator?

author: dosensuppe
author_rank: Contributor
timestamp: June 23, 2025, 09:57:54 am
content: *FL1 is the choke L1 is a low pass filter that will propably become redundant if I add chokes

author: dosensuppe
author_rank: Contributor
timestamp: June 23, 2025, 12:26:41 pm
content: pls help

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 23, 2025, 12:39:24 pm
content: Do you have a specific problem you are trying to solve by splitting the supplies?Do you have any reason to believe splitting the supplies will solve that problem?There are cases where splitting/partitioning analog/digital supplies is beneficial. But if you can't answer the above two questions with confidence, then you should not attempt it. You would likely just create more problems.Quote from: dosensuppe on April 10, 2025, 01:24:55 pmIf by "choke" you mean a simple inductor (not on GND), then that is probably ok. If you mean common mode chokes, then probably not. Would need to see the entire finished schematic, and a diagram showing all external connections, to be sure.

author: dosensuppe
author_rank: Contributor
timestamp: June 23, 2025, 01:17:46 pm
content: QuoteWell. I just want to eliminate as much noise as possible coming from the digital line.That's also why I have a seperate linear regulator for the digital pot.Power Supply Recommendations MCP4251:QuoteKiCAD files attached

author: eugene
author_rank: Frequent Contributor
timestamp: June 23, 2025, 02:41:59 pm
content: If MCP4251 data sheet recommends separate digital and analog supplies and you already have them, then what's the question?Put the MCP4251's and any analog circuitry in one section of the board, all sharing the same AVDD power plane. I would use a single GND plane for the entire PCB.Now pay very close attention to the currents. There will be comparatively small digital domain currents in the SPI lines between the MCU and the MCP4251's. The return currents will flow through the common ground plane, typically directly under the digital signal lines. There will be comparatively larger digital switching currents within the MCP4251's. Since the pots are in the analog power domain, those switching currents will be in the analog domain. The way to deal with those is to be sure that the digital pots have decoupling capacitors right at the chip between the VDD and VSS pins as close to the pins as is reasonable. 100nF is typical. This will help keep the high frequency switching currents confined to the caps instead of polluting AVDD.The coils of the relays will be entirely in the digital domain while the contacts will be entire analog. Fortunately, the footprint allows the relay to straddle the two power planes. Again, always pay close attention to the currents, both digital and analog.It sounds to me as thought you're infected with something called paralysis by analysis. The only sure is to decide at some point that the design is close enough to right and just build it. Don't expect rev 1 to be perfect. But once you have it built, you can go ahead and start planning rev 2. That way you can continue the entertaining design activity while also enjoying music.

author: dosensuppe
author_rank: Contributor
timestamp: August 08, 2025, 12:25:29 pm
content: Ok. I made the board layout, didn't route yet. The relays provide a great physical seperation between analog audio path and digital circuitryI made a seperate thread for this.https://www.eevblog.com/forum/projects/digitally-controlled-preamplifier/