This forum is for posts that might be considered off-topic but that may be useful or interesting to members. Examples include posts about electronics or programming in general, other microcontrollers or interesting devices, useful websites, etc.
I've designed a Zarduino Serial I/O shield which supports the second USART on the Zarduino-40 (and other 40-pin chips) with the options of RS232C or USB, four software UARTs (three RS232C, one RS232-TTL or RS485) and one bitstream input.
All of the ICs handle 3.3V-5V but I cannot be sure what voltage users may employ with RF/IR receivers on the bitstream input (to ZX-40.20). Will clamping diodes and a current limiting resistor provide adequate protection? What size resistor?
The layout JPGs have been added to http://davehouston.org/Arduino.htm but this may need some revision given my special form of dyslexia - so many RX/TX lines are absolutely overwhelming.
dlh wrote:Will clamping diodes and a current limiting resistor provide adequate protection? What size resistor?
I've not been able to find a specification giving the maximum clamping diode current. I suspect that keeping it below 10mA is a good practice. A 5V output driving a 3.3V input through a 1K resistor would result in about 1.5mA of current in the Vcc clamping diode (assuming the clamping diode forward voltage is about 0.2V).
