Re: Can I do this with a uProcessor?

On May 21, 7:52 am, "tempus fugit"
<tocc...@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
[....]
This sounds like you want a micro with a built in DAC or an external
DAC connected to the micro. How smoothly does it need to ramp and how
linear etc?

I just want it to take a few ms to ramp up the relay driver before the relay
switches so that any capacitative clicks are avoided. I don't know if that
needs to be linear or smooth or what (help?)

Ok, so maybe we can strike the DAC out of the specs. A very simple RC
low pass filter will likely do what you need. How high is "high" and
how low is "low"? I'm thinking in terms of using an op-amp if the
signal needs to be bigger than the natural swing of the port pins.


[...]
Well this depends on how many micros I need to do the job. All the outs
would need to be ramped, but if possible, I would like to have 6 outputs -
one to each relay - an probably a max of 4 on at a time.

If you are using an op-amp, they come 4 to a chip. It makes sense to
go up to the next multiple of 4 lines. BTW: Unless I missed
something, we are only talking of one processor to do lets say 24
lines.

[...]
Thankjs for your help Moose - and i'll check out that other site. I'm glad
for any other advice as well.

Look up the following parts and look at the datasheets:

LM340
LT1499
LM324
2N2222
1N4004

I'm almost certain the design will have most of those parts in it. I
suggest the LT1499 for a reason I'm about to explain so that others
don't throw too many stones at me.

The LT1499 is the op-amp I could remember had a rail to rail input and
output and also has diodes across the inputs. Here's the circuit I'm
thinking of:

ASCII art:
----!!-----
! !
! V+ !
! ! !
PORT PIN -/\/\----+----!-\ !
! >---+--- RAMP
Vcc/2--------!+/
!
GND

It makes a nice linear ramp up and down.


.

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