PCM1860 DAC evaluation board - Page 1
Forum section: electronics / beginners

author: AcO
author_rank: Newbie
timestamp: October 14, 2025, 12:26:53 pm
content: Hello good people of the interwebs.I am a self learned engineer that works with a company that deals in sound measuring, processing and analysis . I wanted to learn to design pcbs for a while. So I finally downloaded KiCad and start working on it.I am writing here because I would be grateful for peer review of my first real design. I have done some projects beforehand. Manly copying other people schematics to get the hang of it. They were all audio related because this is my work. But for my first true desing and schematics I chose to try to make an evaluation board for DAC we use in our product. It is TI PCM1860. I wanted to do a board that will allow me to use the ADC with different microcontroles (ESP32, Arduino, Pico ect ...). The adc chip can be hardware controlled so I try to implement it.I would be grateful if some people with more wisdom and knowledge than me look at my work and provide some opinion. As I do not know what exactly I am doing. I would also be grateful for any literature suggestions you people have for me.

author: shabaz
author_rank: Frequent Contributor
timestamp: October 14, 2025, 01:41:09 pm
content: Hi,I've not used this part, but here are (some mostly general) suggestions.(1) The mic input looks incorrect, it is worth checking the datasheet, for example figure 64 (there may be better figures, I didn't look in detail), you can see that the mic bias needs to go to one electret mic element connection via a resistor, and then then that same connection goes to the audio input via a capacitor. The other end is connected to GND.(2) Voltage selection capability is incorrect. When bypassing the LDO, no DC can flow because you've wired C2 in series. In general you need to be more rigorous with your examination of the circuit, because there may be more errors like this, and these are not really excusable even on a first PCB, because they are not subtle mistakes.(3) You don't have any pin header for the audio connections. You appear to have a connector for the mic, but you may wish to attach other test equipment, so it's a good idea for a dev board to also have pin headers perhaps.(4) Use resistors to isolate things. For instance, you have hard-coded mode connections (apart from one switched mode) which might be fine, but if you're in the slightest doubt, then it could be useful to insert zero-ohm resistors instead, so you can desolder and patch with wires any incorrect mode settings later.(5) Use jumpers to isolate your supplies. Currently you have the analog and digital supplies hard wired together, you may wish to use jumpers or zero-ohm resistors to make the connections, so you can optionally isolate things (also even just to perform current measurements).(6) Examine your product PCB and schematics. It could be helpful to explore how it is used in your product, so that you design your board to be compatible or relatable for instance. As an example, if your product uses line inputs too, then bring out those connections to pin headers too.(7) Label things. Your pin headers and jumpers currently have no silkscreen labels.( 8 ) Ground connections: add a couple so you can more easily clip a 'scope ground connection on, when troubleshooting.(9) Make absolutely sure to run a Desgn Rules Check (DRC) on the PCB, and follow up on each error/warning.In general I think it's a great idea to make a dev board like this to learn from, once you make those changes and possibly even redo some or all traces (personally I cannot route tidily the first time) then hopefully you'll be in a good position to get the PCB built, and it's good that you did a review. Give yourself at least a 24 hour cooling off period before ordering the PCB, in case you think of any changes you still wish to make.

author: AcO
author_rank: Newbie
timestamp: October 14, 2025, 05:31:00 pm
content: Thank you this is just what I needed. I know I will make stupid mistakes but that is the price you pay when you are self learned. The board is not yet finished it is work in progress, but I felt I can go and show it to people.As for mic connection it is build for specific mic (micw 436i) I have a bunch of them laying around as we use them in production. We use molex 2 pin connector on board for mics and that was my idea just grab the mic part I already have and plugged in. But I will put some more headers for audio because it is a good idea.I especially appreciate the general hardware design advice you give me (ground connection, 0 ohm resistors, ect). I kinda showed me the way you have to think. Questions I have to ask my self. How you will debug this? How will you measure this? What if you mess this up, can you fix it. It is quite different then running code. Hardware is way less forgiving. I thank you again for your advice and I will try to implement as much I can in my design. I would also ask what did you meant by tidy traces? What general rules should I follow when tracing. I general I try to keep the analog part far from digital and power and I try to make ground loops short.