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NE555 / timer question

J

Jon Yaeger

Jan 1, 1970
0
I have a 5 volt supply application where I want to have an output signal go
high and stay there after 5 or so seconds.

Every circuit I have seen using the ubiquitous NE555 timer recycles
eventually.

Is there a simple solution to the problem, or should I look for another
circuit for a time-delay?

Thanks in advance.
 
I have a 5 volt supply application where I want to have an output signal go
high and stay there after 5 or so seconds.

Every circuit I have seen using the ubiquitous NE555 timer recycles
eventually.

Is there a simple solution to the problem, or should I look for another
circuit for a time-delay?

Thanks in advance.

74LS123 or similar.
Or better yet, in the 21st century we use 8 pin microcontrollers.
 
D

D from BC

Jan 1, 1970
0
I have a 5 volt supply application where I want to have an output signal go
high and stay there after 5 or so seconds.

Every circuit I have seen using the ubiquitous NE555 timer recycles
eventually.

Is there a simple solution to the problem, or should I look for another
circuit for a time-delay?

Thanks in advance.

For :

+----------------+
| |
| |
| <----5 Secs--> +---------


RC + bipolar transistor
RC + mosfet
RC + gate (schmitt)
RC + comparator
RC + regulator with shutdown
Isource + C variations of above.
oscilllator (1) + counter + gates
oscillator + shift register + gates
one shot IC or quivalent
uC

Offbeat Ideas
Thermistor + transistor
PC port + software

(1)Maybe use line frequency from transformer.
Clock radio style.


D from BC
 
J

Jamie

Jan 1, 1970
0
Jon said:
I have a 5 volt supply application where I want to have an output signal go
high and stay there after 5 or so seconds.

Every circuit I have seen using the ubiquitous NE555 timer recycles
eventually.

Is there a simple solution to the problem, or should I look for another
circuit for a time-delay?

Thanks in advance.
Use a monostable mode config..

Since a low signal is needed to
start the trigger, Use a PNP transistor
to pull down the timing cap to common while
the input trigger signal is being held down.
this keeps the cap from charging and holds the
timer from expiring.
when you release the input from the trigger so
won't the PNP transistor you put in there to keep
the cap from charging. when this happens, the
cap will then start to charge and force the 555 output
off when it reaches 2/3 of the Vcc voltage.

http://www.uoguelph.ca/~antoon/gadgets/555/555.html
Look at the monstable example there and add the
pnp transistor.. Collector to common , emitter to the
cap (pin 7/6),. use something like a 1k ohm resistor
to bias the transistor from the same signal used to
trigger the input.

P.S.
this is a retriggerable configuration, meaning, if
the input signal gets seen before the timer expires, the
pnp transistor will discharge the cap and start the time
off delay again with out any notice on the output..
if that is ok then you're all set.
I think for the most part, this is what you want.
 
J

Joerg

Jan 1, 1970
0
74LS123 or similar.
Or better yet, in the 21st century we use 8 pin microcontrollers.


Oh man, a micro for something this mundane? You can do that with 1/6th
of a 74HC14, one resistor, one FET and one cap. Comes to under 10 cents.

R to VCC and input, C to input and GND, FET across cap, done.
 
M

mc

Jan 1, 1970
0
Oh man, a micro for something this mundane? You can do that with 1/6th of
a 74HC14, one resistor, one FET and one cap. Comes to under 10 cents.

R to VCC and input, C to input and GND, FET across cap, done.

You can also do that with a 555. (If I understand right that he wants
output to be low for the first 5 seconds, then go high and stay there.)

C from Vcc to input (which is pins 2 and 6 tied together), R from input to
ground; pins 4 and 8 to Vcc; ground pin to ground; pin 3 is output.

If memory serves me right!
 
B

BobW

Jan 1, 1970
0
Joerg said:
Oh man, a micro for something this mundane? You can do that with 1/6th of
a 74HC14, one resistor, one FET and one cap. Comes to under 10 cents.

R to VCC and input, C to input and GND, FET across cap, done.

Most people will never be able to learn what an R, C, FET, VCC, or GND is.
Remember that 50% of all people are below average. You're expecting too much
from them, Joerg.

Bob
 
Oh man, a micro for something this mundane? You can do that with 1/6th
of a 74HC14, one resistor, one FET and one cap. Comes to under 10 cents.

R to VCC and input, C to input and GND, FET across cap, done.

How about a 12AU7 dual triode? Why use semiconductors for something so
mundane?
Maybe it's availability and learning something relevant? With the uC,
you can do it with no external parts, and much more flexibility.
The upfront work pays off when all of a sudden he wants a 1 second
pause between turning off and on again, etc...
 
F

Frank Buss

Jan 1, 1970
0
Jon said:
I have a 5 volt supply application where I want to have an output signal go
high and stay there after 5 or so seconds.

How much power needs the output signal? One solution would be something
like this:

http://img406.imageshack.us/my.php?image=delaynt4.png

R4 is needed to discharge the capacitor (Joerg, how do you do this with one
resistor?), which means after turning off the power, the full delay is
available again after some 20 seconds power down. With Rpoti adjusted to
about 20k I've managed to get a 5 second delay (not only in ltSpice, but on
my breadboard, too :)
 
J

Jan Panteltje

Jan 1, 1970
0
How about a 12AU7 dual triode? Why use semiconductors for something so
mundane?
Maybe it's availability and learning something relevant? With the uC,
you can do it with no external parts, and much more flexibility.
The upfront work pays off when all of a sudden he wants a 1 second
pause between turning off and on again, etc...

HAS ANYBODY MENTIONED SMALL ELECTIC MOTOR WITH CAMSHAFT AND CONTACTS YET?
 
J

John Fields

Jan 1, 1970
0
I have a 5 volt supply application where I want to have an output signal go
high and stay there after 5 or so seconds.
 
J

Joerg

Jan 1, 1970
0
How about a 12AU7 dual triode? Why use semiconductors for something so
mundane?


I'd do it with a nuvistor ;-)

Maybe it's availability and learning something relevant? With the uC,
you can do it with no external parts, and much more flexibility.


Learning something relevant is exactly the problem but not in the way
you decribed it: IME young grads often do not even know how to create a
one-shot out of simple parts anymore. All they can do is write code,
VHDL and wield PSPICE. Soldering iron? Nope. Analog parts? Yuck. Mention
tapped inductors and they might think it's some kind of newfangled
cholesterol medication.

Yes, it may only be one part. But what does that part cost in large
quantities? And what does the semi-discrete solution cost? How does the
little uC fair in brown-out? I can count anymore the times I found uCs
as the culprit. "Well, the datasheet says it has some kind of POR" ...
"Ok, let's gradually decrease VCC and then raise it again" ... "Oh drat!"

The upfront work pays off when all of a sudden he wants a 1 second
pause between turning off and on again, etc...


Then out of the blue that nice little uC goes unobtanium and, of course,
like usual there ain't no 2nd source.
 

neon

Oct 21, 2006
1,325
Joined
Oct 21, 2006
Messages
1,325
what you want to do is actualy easy with an lm555 use pin 2 to trigger going low pin 3 will stay hi until your time elapses no matter what pin 2 does if you want to interupt the time then bring pin 4 low as a reset. easy thing is series cap with a pull up. 50 uamps need to get it startedgood luck.
 
F

Fred Bloggs

Jan 1, 1970
0
BobW said:
Most people will never be able to learn what an R, C, FET, VCC, or GND is.
Remember that 50% of all people are below average. You're expecting too much
from them, Joerg.

Bob

50% of people are below the median but not necessarily the average-
could be way more or way less.
 
F

Fred Bloggs

Jan 1, 1970
0
Jan said:
HAS ANYBODY MENTIONED SMALL ELECTIC MOTOR WITH CAMSHAFT AND CONTACTS YET?

Nonsense, a heater and bimetal...although 5 seconds may be pushing the
lower boundary of obtainable.
 
J

Joerg

Jan 1, 1970
0
Fred said:
Nonsense, a heater and bimetal...although 5 seconds may be pushing the
lower boundary of obtainable.

Nah, use the chain of a coocoo clock. Tick-tock-tick-tock .. click :)

Since we got it and I repaired it (one of those honey-do projects...)
that thing never failed, despite the fact that it looks rather flimsy.
Ok, the air brake wheel is still busted because they made it from
plastic. Arrgh! My gut feel is that some tourists are being ripped off
quite a bit.
 
D

D from BC

Jan 1, 1970
0
Nonsense, a heater and bimetal...although 5 seconds may be pushing the
lower boundary of obtainable.

I haven't checked for very slow blowing fuses.
I wonder if this goofy circuit can go low in 5 seconds..

V+ V+
| |
R R
| /-----Vout
+-------|
| >
fuse |
| |
gnd gnd


D from BC
 
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