I'm working on a TTL to RS485 transceiver which is part of a bigger project (arduino based) and I came up with the following design:
I have a few questions:
1) I have seen very different values for the resitors R23 and R25 from 1K up to 20K. I have decided to use the most common value I have seen in other designs 4.7K but I don't really know if it's a good decision and how to calculate a proper value.
2) D11, D12 and D13 are used to protect against transition voltages, are the choosen ones correct? I have seen some designs including fuses, is it a good idea for extra protection?
This project is arduino based and it will be a network of 32 devices conected via RS485 so any idea to improve and protect the communication will be a great contribution.
Updated schematic to reflect the suggested changes: