RS232 level shifting power consumption

upand_at_them said:

How did you arrive at the pullup value? I'm using 2K and it works, but I was curious since 2K7 seems an odd value (for me at least).

Click to expand...

2K7 is an E12 preferred value, it's 2K which is an odd value!, it's in the E24 series.

Pullups are not normally at all critical, there's usually a maximum current limitation, so you can't go too low, and usually a minimum current required to actually pull the connection high - you chose a value anywhere in between, based on your requirements.

I have 2.2K resistors...that's a common value. I'm not familiar with E12 and E24.

Mike

upand_at_them said:

I have 2.2K resistors...that's a common value. I'm not familiar with E12 and E24.

Mike

Click to expand...

E12 and E24 are resistors ranges, with E12 being a subset of E24.

So E12 has 12 values per decade, and is used for 5% and 10% values, these are the most common values, they go:

1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2

E24 has these 12 values, plus 12 more - there are also ranges with more values. E24 is usually used for 2% and 1% resistors - and I can't be bothered to type the extra 12 numbers :lol:

As Nigel says, the pull-up resistor value isn't critical... Don't go too high though... You'll find a 10k value won't pull up fast enough for 115200 baud operations...

Regards, Mike