Re: Timer Circuits or PIC
- From: John Fields <jfields@xxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 13 Sep 2005 08:30:53 -0500
On Tue, 13 Sep 2005 11:30:45 +0100, "Rob Convery"
<rob@xxxxxxxxxxxxx> wrote:
>I am working on a project where I am going to be controlling a number of
>rams. These are triggered using solenoids. I am trying to work out the best
>method of controlling these. The whole setup will have 5 instances of the
>setup described below (this may effect how you suggest doing this). I am
>working in a environment with a supply voltage of +12v.
>
>I have a single pulse trigger which I need to subsequently operate 2 outputs
>using delays using a 2nd input to decided what to trigger. In Summary.
>
>Trigger input pulses High
>If Input Z if ground Then
> Output A must go high for X (approx 5-10) seconds
> &
> Output C must delay for X (probably 2), then high for X seconds
>(probably 2)
>else
> Output B must go high for X (approx 5-10) seconds
> &
> Output C must delay for X (probably 2), then high for X seconds
>(probably 2)
>end else
>
>or pictorally
>
>Trigger ___|-|_______________________
>InZ _____________________________
>A ____|-------------------|____
>B _____________________________
>C __________|--|_______________
>
>OR
>
>Trigger ___|-|_______________________
>InZ -----------------------------
>A _____________________________
>B ____|-------------------|____
>C __________|--|_______________
>
>(Copy above to notepad if it displays incorrectly)
---
Copying to notepad won't help...
If this is what you mean:
t0-->|_ t0-->|_
Trigger ___| |_________________..._____| |_____________________
____ __________________________
InZ ____|______________________...__|
_______________
A _________| |___..._____________________________
|<--- 5-10s --->|
_______________
B _____________________________..._____| |_______
|<--- 5-10s --->|
___ ___
C _____________| |___________...________| |________________
2s-->| |<-- 2s-->| |<--
-->| |<--2s -->| |<--2s
---
>So what is the best way of implementing this. Should I use a combination of
>timer circuits to do this but with having 5 of these it would become a mass
>of timer circuits. Alternatively I could program a PIC or PICs do to this (I
>have never done PIC programming - well other than some traffic light thing
>during electronics at Uni, but should be able to pick it up as I am a
>programmer/tester by day)
---
If you build it out of glue logic then you'll need a timer for A,
one for B, one for C, and one for the delay before C. You'll also
need an inverter to select between A and B, so if the timers are
dual one-shots like 4538's or HC123's it'll cost you 4 chips per
channel plus four timing caps, four timing resistors (probably pots
if you're not sure what you timing requirements will be). Also, for
the board, one hex inverter and one RC for the power-on reset.
That's 11 chips and 42 discretes total, versus a single
microcontroller and a ceramic resonator if you need better accuracy
than you can get with the µC's internal clock oscillator.
If you write code for the µC, the choice of which way to go is
pretty much a no-brainer, huh?
BTW, you could use a single timer for A and B, but then you'd have
to steer its output, which would cost you three quad 2-input ANDs.
So your savings in one-shots(2 chips) would be offset by the need
for the three quad 2-input ANDs, so that would cost you an extra
chip. You'd save ten discretes, though...
Still a no-brainer, I think.
--
John Fields
Professional Circuit Designer
.
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