Re: Design considerations for (2m) long signal lines
- From: John Larkin <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Thu, 19 Jul 2007 08:04:36 -0700
On Wed, 18 Jul 2007 11:40:55 -0400, "Peter S. May"
<psmay@xxxxxxxxxxxx> wrote:
I'm working on a microcontrolled LED lighting setup in which breakout
boards with eight outputs each would be connected to the microcontroller
board by cables (CAT-5 is what's on hand) at a length of somewhere
between 1m and 3m. The breakout boards would contain some sort of
D-type flip-flop or latched parallel-out shift register with outputs
connected to transistors that then drive the LEDs. Using a shift
register would have three signal lines (signal, shift clock, latch
clock) and two supply lines.
I need sort of a run-down of the design considerations I need to account
for, and I'm not sure where to look. Are decoupling capacitors (say,
.1uF) going to be enough to keep the ground stable?
Probably.
Will putting
Schmitt triggers on all the input signal lines of the breakout boards
help?
Absolutely. Even better if you put an r-c lowpass filter at the input
of each schmitt, to nuke any cable ringing. Use HC-type schmitts.
Without resorting to differential signaling, what limits will I
run into for the data rate? Will a long cable make a significant
addition to propagation delay?
If you run single-ended, unterminated, and use maybe 1 us tau r-c's in
front of schmitts, figure 200 kbps is safe, 2.5 us high/low levels. A
hundred feet of cable would be OK, if you don't have ground loop
problems.
If you need to go faster, more care will be required, preferably
terminated differential levels.
John
.
- References:
- Design considerations for (2m) long signal lines
- From: Peter S. May
- Design considerations for (2m) long signal lines
- Prev by Date: Re: USB Syntax?
- Next by Date: Re: Using 74xx574 D FF to expand PIC outputs
- Previous by thread: Re: Design considerations for (2m) long signal lines
- Next by thread: Re: Design considerations for (2m) long signal lines
- Index(es):
Relevant Pages
|
