I’m new to PCB design and currently learning how to use KiCad. I’m encountering some issues with my schematic design and could use some assistance.
Firstly, I’m getting errors in the Electrical Rule Check (ERC), and I’m not sure how to resolve them. Secondly, as I’m still learning, I’d like to ensure that my schematic is accurately created according to the datasheet provided. If there are any discrepancies or errors apart from the ERC issues, I’d appreciate your feedback.
I’ve attached the schematic file for reference. Any help or guidance you can provide would be greatly appreciated. Thank you in advance.
I’ve uploaded the entire project along with an image displaying the error, as well as the datasheet for the MEMS microphone, here.
Welcome to the forum. You’ve been ‘leveled up’ so you can post files. I think you can archive your project and just upload that. You can edit your initial post with it rather than start a new one for that.
The ERC is a nice helper but, in the end, it is the designers responsibility to check the design.
Thank you for your assistance with the ERC issues. They have all been resolved, and I’m sharing the revised schematic for your review. However, I noticed one test that was ignored. Is there a way to address this as well?
Regarding your comment about Cd1 being only connected to Ca1 and Cb1 - this information was taken directly from the datasheet. Could you please review my schematic again and identify any potential issues? I’m still unclear about what needs to be changed. Your guidance would be greatly appreciated.
Thank you for your assistance. I’ll eagerly await your response. This project marks my first endeavor, and I’m hopeful that with the guidance of skilled individuals like you, it will lead to success. My aim is to continue refining my skills, creating more PCBs in the future, and offering assistance to others in the community.
Which to me makes more sense. However I know nothing about this and would point you to a more dedicated electronics forum (EEVblog) to get the circuit described in more detail and if you have problems drawing this in Kicad come straight back !
Datasheet author didn’t care about little things like dots at points where the connection was obvious
In that schematic capacitors are certainly connected to Out+ and Out- lines. In other case they are no sense there.
Not reading the datasheet in detail I’m almost sure that this schematic there is not application schematic. It is the schematic to show with what external load (these are not internal elements) parameters you can read in Table 6 were measured.
I have never used such microphones but I suppose the signal to be used is differential and not common mode. This circuit makes common mode point (VCM) to specify its value in Table 6.
The amplifier driven by this microphone can have its own common mode polarization and be separated from microphone by capacitors or it can use common mode polarization offered by microphone. It is amplifier developer decision if he wants to extra load microphone with its amplifier input polarization circuits or not.
I’ve taken a look at the page you mentioned in the datasheet, and I also found some helpful information on the link below. While I’m not entirely confident in my understanding, I’m open to any feedback or insights you may have. Your input would be greatly appreciated.
Looking only at Figures (no time to read) - Figure 3 is probably the correct way to use this microphone.
I’m not sure what for is the common mode voltage measurement in datasheet. I suppose that DC voltage difference between both outputs is bigger than AC signal so can’t be used together with AC for amplifier input. But you can imagine to have two voltage followers driven directly (with polarization) from microphone outputs and then DC separated from AC (with capacitors) after these followers. To do such design knowing the expected common mode voltage would be necessary.
Looks for me correct if it is only the PCB to be able to use that microphone in some other design.
Practically I suppose such microphones should be used directly at destination PCB and not through using small PCB at bigger PCB.
But I didn’t checked anything like if pins are correctly numbered and so on.
@Piotr For the initial phase, I am focusing on testing this Mems Microphone with an ESP32 Dev Board to understand its working and utility. In subsequent iterations, my goal is to tailor the usage of this Mems Microphone for specific applications and refine it further. I am currently exploring the addition of a Differential Amplifier to avoid handling it solely on the code side. I would greatly appreciate it if you could take a quick look at the pins and the schematic and provide your feedback. Your insights are invaluable to me. Also, I have selected certain capacitor values, and I hope they are suitable without requiring any changes. Thank you once again for your support.
Check everything yourself. The problem is not what pin numbers you used at schematic (what looks being correct as in datasheet) but if the correct functions are assigned to right footprint pads. Easiest way is to have pin numbered as in datasheet, but when you use made by someone else footprint you have to check also if its pads are numbered as in your datasheet.
What have happened with circular pin/pad 5 that looks also needed to be connected to GND (I have not read anything - may be somewhere there it is said that you can left it not connected).
I was playing with circuit for microphone (dynamic one) last time in 1977. Being in secondary school final award class I made my desk lamp being switched on/off by clapping hands. Those my circuit (germanium transistors) was made in the air without any PCB in the form of a spider on a newspaper and took up more than half of the shelf in the bookcase over my desk. Since then I have noting to do with amplifying microphone signals.
