input voltage query

[tarantulataramasalata]

I am using a picaxe 08/M powered by 6v, as per instructions in the datasheets. Is it ok to activate an input using 9v, configured with a 1k protection resistor an a 10k pull down, as per the datasheet?

 

[hippy]

It's no longer recommended to power an 08 or 08M from anything more than 5.5V.

According to one Microchip datasheet I have, the maximum current injection to any I/O pin should not exceed +/-500uA ...

ww1.microchip.com/downloads/en/AppNotes/00521c.pdf

Based on the 22K used for +/-12V serial, for a 9V signal, something around 18K would seem to be the right value, and of course you can go higher, maybe even 100K.

Edited by - hippy on 17/06/2006 17:12:17

 

[tarantulataramasalata]

quote 'Based on the 22K used for +/-12V serial, for a 9V signal, something around 18K would seem to be the right value, and of course you can go higher, maybe even 100K.'

thanks hippy. could you explain what this bit is for - a potential divider praps? to reduce the supply from 6v to 5.5v, or to limit the current to the input from 9v?

thanks

 

[hippy]

Current limiting, as per the download circuit, rather than a divider. So the 18K goes from '9V' to PICAXE I/O, 10K pull-down from '9V' to 0V.