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I am building my OS 3.4 DC version. I am wondering why there are CH224A and CH224Q (U0 and U1) combined in the circuit as they fulfill the same purpose. Are they considered as used alternatively or do I need both at the same time?
https://github.com/OpenSprinkler/OpenSprinkler-Hardware/blob/master/OS/3.4/DC/OS34DC_schematic.pdf
Additional question: Which resistor footprint is commonly used? I ordered a mix of 0603 and 0402, but the 0402 seem pretty small on the pcb. Now I am thinking it would have been better to use 0603 for all resistors (except R13).
1) CH224A vs CH224Q: it’s to prepare for supply chain issues. Sometimes one of them is out of stock. This is common practice in circuit design: put two packages of the same chip on the PCB and select one of them based on which is in stock at the time of ordering.
2) For DIY I would recommend 0603 as it’s much easier to work with. 0402 is very small, and there are no markings on it, making it hard to check the resistance value by just looking at it.
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