Simple 2 layer boards can be designed based on clear images. For complicated boards involving ICs can be designed precisely based on physical product(I'm not sure if you can deliver product to me). We need to disassemble all parts and study on datasheet of ICs as well.
- study on block diagram and schematic of your product
- draw schematic while checking datasheet of ICs
- we need to detect all the ICs and connector part numbers. suggest substitution for components not in stock
- we need to measure all the value of passive components and polarity
- review schematic design based on circuit design experience and similar circuits
- measure detailed dimension for PCB
- imitate PCB routing or optimize board size based on your requirement
-fabrication files for manufacturing (BOM, gerber, drill, 3D PCB..)
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