I’ve had trouble at several occasions with microcontrollers directly fed from an external power supply.
I recommend to add an inductor to filter the power supply right where the power enters the PCB.
Especially when working with breadboards, and nearby switching FL or halgogen ligts.
Excessive noise is either coulpled directly via the mains net and the cables, or the power cable may have worked as an antenna and picked up the noise.
If your power supply is properly built though, it already has an adequate filter built in.
Interesting read.
A comment on the PCB: I don’t see any mounting holes. There was a question about if the mounting holes connected to ground or not. I’ve taken the mounting hole closes to wherever power comes into the board and place a small 2-pin connect between the mounting hole pad and the ground plane. That means you can deal with that later. KiCad has a “mounting hole” that is a pad.
The footprint for the pad would be like a “MountingHole_4.3mm_M4_Pad_Via”
I would also say that when you mount this, pick a spacer height where you can also get rubber feet in the same height. A common spacer height and foot height might be .25". You can then place multiple rubber feet in and around the screw terminals so that the force of the screwdriver tightening up any connections (or if it’s a pin connector, the force of plugging in something) will not flex the board too much.
Of course when you unplug a connector, you will have to press down on the board with your other hand and be careful. But at least when plugging something in or screwing something down, the board will not be unduly flexed.
I understood that 5V will be used for relays and the rest of electronic will got power from regulated locally 3V. Regulator filters noise up to some frequency. But filter at input of course should be used.
I completely don’t know what are the needs of sensors as their grounds (as I understood) can’t be connected permanently together. If so then when sensor gnd is connected to PCB GND than isn’t any problems with that. External supply isolates but has rather high capacity across isolation. May be common mode choke should also be used (at power supply or at sensor connection or both).
Everything depends on many factors.
Yes, indeed.
Cosmin clearly does not have much experience with electronics, and I do not have much interest in taking over the project and finishing the PCB. I do not know how stringent the demands on those sensors are. Spikes from switching mains appliances (FL lightning anything with mains frequency transformers) go right through linear voltage regulators so indeed, power supply filtering is quite important for a reliable product. (Without it, it will probably work 99% of the time).
eepete also has a valid point. Especially with PCB with screw connectors you need good support under the screw connectors to not bend the PCB too much while screwing in wires. With this PCB it’s not so critical, but SMT resistors and capacitors can easly crack and cause open connections or shorts in such conditions.
As Paul said, I don’t have much knowledge of electronics … in the sense that I understand in principle but I don’t have the ability to come up with solutions or calculate / deduce component values, etc. For example, I know what an inductor is but I don’t know how to calculate what inductance I need to filter the input. So, it helps a lot if you develop your idea a bit, if you can, give me something more specific like: use piece X with Y value in series with the imput, etc.
This forum is more geared towards using Kicad. We’ve let this slip a little but the release of V6 has really increased the traffic. This forum may be better suited for general electronic questions:
You don’t
You know what an ideal inductor is, but there are no such in real life. Specially when we speak about disturbances and its filtering. Most frequently used elements to filter high frequency disturbances are ferrite beads. These are inductors but in their datasheet you will not find (or it will be hard to find) their inductance. They are classified by impedance (being mostly resistance and not inductance) in Ω: https://www.mouser.com/datasheet/2/281/ENFA0003-1915778.pdf
I can’t. I have never worked with any kind of sensitive sensors. I don’t know if yours are sensitive or not, if your power supply is classical (trafo+bridge) or modern (DC/DC), if it is well done (low common mode emission) or as cheap as possible (higher common mode). Do this common mode noise is acceptable for sensors or not, and so on. May be there are no problems with that at all.
I am using common mode choke at RS485 communication lines what has nothing to your case.
But coming back to the knowledge of what inductor is - the common mode chokes offered by producers are classified not only by inductance but also by the way they were wound. So for example here you can find two identical (2x10uH) but different inductors (see Winding Style column):
