[sci.electronics] Build a "simple" timing device.

ba@m-net (Bill Allen) (09/04/88)

My (ONLY!) knowledge of electronics:
o I can buy parts at Radio Shack if given the part #s.
o I can read.
o I can follow instructions.
o I can soldier.

I need to build the follow device:
You hit a button on a very small box.  25 seconds later a
gentle beep is heard.  A second beep 3 seconds later.  A
third and final beep after an additional 2 seconds.  (That's
25-28-30 secs).   The unit then resets itself awaiting another
button press.

Accuracy need only be +/-0.25 second.

Sounds simple?
-- 
---------------------------------------------------------
Reply-To: ba@m-net.UUCP (Bill Allen Beogelein)
Organization: M-NET, Ann Arbor, MI
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lemke@Apple.COM (Steve Lemke) (09/06/88)

In article <2283@m2-net.UUCP> ba@m-net.UUCP (Bill Allen) writes:
>I need to build the follow device:
>You hit a button on a very small box.  25 seconds later a
>gentle beep is heard.  A second beep 3 seconds later.  A
>third and final beep after an additional 2 seconds.  (That's
>25-28-30 secs).   The unit then resets itself awaiting another
>button press.
>
>Accuracy need only be +/-0.25 second.
>
>Sounds simple?
yes, as a matter of fact...
>---------------------------------------------------------
>Reply-To: ba@m-net.UUCP (Bill Allen Beogelein)
>Organization: M-NET, Ann Arbor, MI
>---------------------------------------------------------

Go to Radio Shack and get a 558 quad timer chip.  If they don't have one, get
two 556 dual timer chips, and if you're at strike two, get three 555 timers.
The package may or may not have enough details on the back (probably not), so
you might find a book on using the 555 series (they all work the same).  You
want to set up the first on with the resistors and caps set to trigger at 25
seconds, which sounds your alarm and starts the second timer which triggers
at 2 seconds, sounds another alarm, and starts the third timer which triggers
at 3 seconds and sounds the final alarm.  If you want to use the same alarm,
you might use a three-input or gate tied to the three outputs.  Also, depending
on the alarm, you might want to use a fourth timer as a "one-shot" to only
sound the alarm for as long as you want it to be on.

Unfortunately, I don't have any of my data books nearby, so I can't give you
an exact schematic (and some things are still left unspecified, such as the
alarm you want to use and if you want to use three different ones or the same
one).  Perhaps you can answer these additional questions and someone can pro-
vide a schematic for you if you can't find something helpful in a book at RS.

			===== Steve Lemke =====
Internet : lemke@apple.com       UUCP: {sun,voder,nsc,decwrl}!apple!lemke
AppleLink: LEMKE                GEnie:  S.Lemke
All opinions are, of course, mine, and could never belong to anyone else!

cep4478@ritcv.UUCP (Christopher E. Piggott) (09/06/88)

Would you explain to me how the delay function works on the 555?  I have a
few of them, as well as a few of the dual packages (did not know they make a
quad version), and have been wanting to use one as a burglar alarm entry
delay, but I don't understand the cooncept of R.C. components and how they
work (question 1: what are the units, ohms and microfarads?) and how come it
requires three pins to set the delay?

						/Christopher

till@didsgn.UUCP (didsgn) (09/06/88)

In article <809@ritcv.UUCP>, cep4478@ritcv.UUCP (Christopher E. Piggott) writes:
] Would you explain to me how the delay function works on the 555?  I have a
] few of them, as well as a few of the dual packages (did not know they make a
] quad version), and have been wanting to use one as a burglar alarm entry
] delay, but I don't understand the cooncept of R.C. components and how they
] work (question 1: what are the units, ohms and microfarads?) and how come it
] requires three pins to set the delay?

PLEASE! BUY A BOOK!
(what's an ohm? what's a farad- not to speak of microfarad? ?????
Does a Kzin like tomatoes for lunch?)

With all due respect, but please invest the time and money to go to one
of those places where they sell things made from lots of leaves of
rectangularly cut paper- on which you might find letters that form words
and sentences. These are then bound together to form something called
'books'.
Amazing stuff that...

gil@limbic.UUCP (Gil Kloepfer Jr.) (09/07/88)

In article <809@ritcv.UUCP> cep4478@ritcv.UUCP (Christopher E. Piggott) writes:
|>Would you explain to me how the delay function works on the 555?  I have a
|>few of them, as well as a few of the dual packages (did not know they make a
|>quad version), and have been wanting to use one as a burglar alarm entry
|>delay, but I don't understand the cooncept of R.C. components and how they
|>work (question 1: what are the units, ohms and microfarads?) and how come it
|>requires three pins to set the delay?
|>
|>						/Christopher

[Hi Chris -- Long time no write .. sorry about that]

Funny you should ask this -- I just needed to know something about this
for an eprom programmer I was making (My 3B1 now is an eprom programmer
too :-).  Here's what you probably need:

	Charge time:		T = 0.693(Ra + Rb)C
	Dischage time:		T = 0.693(Rb)C
	Total period:		T = 0.693(Ra + 2Rb)C
	Oscillation Freq:	f = 1/T = 1.44 / ((Ra + 2Rb)C)

	I believe R's are in ohms and C's are in farads (ie. 1uf is
	1E-5 farads).

[From the Radio Shack Semiconductor Reference Manual, reprinted without
permission]

To use a 555 timer in a "one-shot" mode, connect resistor Ra from Vcc
to pin 7, Rb from pin 7 to pin 6, and C from pin 6 to ground.  Pin 2
is the "trigger" pin.  In the free-running mode (where it would oscillate),
you would connect pin 2 to pin 6.  Of course, you connect pin 8 to Vcc and
pin 1 to ground in all cases, and pin 3 is the output pin.  Pin 4 is labeled
RESET and pin 5 is the control voltage, but I forget how to use those :-(.

If I remember correctly, the 555 timer works by measuring the time it takes
to charge a capacitor to 2/3 Vcc, but don't quote me on that one.  I believe
that once it charges to 2/3 Vcc, pin 7 sinks to ground and the capacitor
is discharged through Rb until it reaches zero (?? is this correct??).
Then the cycle begins once the trigger is brought to ground again.

I'm sure that a *real* EE out there can explain it better than this, but
this is as good as I can get from memory (and as a CS-type at that :-).

+------------------------------------+----------------------------------------+
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lemke@Apple.COM (Steve Lemke) (09/07/88)

In article <809@ritcv.UUCP> cep4478@ritcv.UUCP (Christopher E. Piggott) writes:
>Would you explain to me how the delay function works on the 555?  I have a
>few of them, as well as a few of the dual packages (did not know they make a
>quad version), and have been wanting to use one as a burglar alarm entry
>delay, but I don't understand the cooncept of R.C. components and how they
>work (question 1: what are the units, ohms and microfarads?) and how come it
>requires three pins to set the delay?

I don't remember all the specifics (although I've used them before).  Anyway,
you get to control the frequency (assuming astable operation - meaning it will
keep cycling on and off) as well as what part of the cycle it is on (and there-
fore what part it is off).  As I said, I don't remember what the constants are
but if someone has a data book handy perhaps they can look it up for us...

			===== Steve Lemke =====
Internet : lemke@apple.com       UUCP: {sun,voder,nsc,decwrl}!apple!lemke
AppleLink: LEMKE                GEnie:  S.Lemke
All opinions are, of course, mine, and could never belong to anyone else!

myers@hpfclm.HP.COM (Bob Myers) (09/09/88)

>	I believe R's are in ohms and C's are in farads (ie. 1uf is
>	1E-5 farads).

No, 1 MICROfarad (1 uF) is 1E-*6* farads.

Another inconsequential error of an order of magnitude :-).


Bob Myers  KC0EW                         |  Opinions expressed here are not
                                         |  those of my employer or any other
{the known universe}!hplabs!hpfcla!myers |  sentient life-form on this planet.

sukenick@ccnysci.UUCP (George Sukenick) (09/09/88)

Re: using a 555 timer as a  one shot timing device:


One thing to consider when using 555's : some varieties,
in some "one shot" configurations,
when triggered, will turn the output on for a time as defined by
the RC  combo regardless of the duty cycle of the trigger
(ie: the output of the 555 will go high for the prescribed time);

others will ADD the on time of the trigger to the time of the
RC (ie: the output of the 555 will go high when activated and the RC
timing will not go into effect until the trigger signal goes off).

This extra time can be significant when connecting to mechanical switchs.