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KA , 12-27-2024, 02:40 AM

Hello everyone!

I've been examining a schematic for a working product and have some questions about the resistor values used for different communication lines and components. Specifically, the schematic uses 220 ohms for UART, 120 ohms for I2C, 22 ohms for switch inputs, and 68 ohms for LED outputs. These components are connected to an STM32 MCU via a mezzanine connector, with the lines being approximately 100mm long.

Are there standard guidelines or rules of thumb for selecting resistor values based on different protocols, or are these values typically determined through experimentation? I'm hoping to streamline my BOM and reduce the need for extensive testing. Any advice or insights would be greatly appreciated!

Robert Feranec , 12-27-2024, 07:06 AM

this doesn't seems to me like a standard, more like solving/preventing problems for a specific application. They could choose these resistors maybe based on cables/boards which are connected to this specific device, but if it is only for 100mm they should not experience any problems.