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need help with 555 delay timer

G

gretsch27

Jan 1, 1970
0
What I need is a simple circuit for a 5-10 second delay. No voltage
for 5-10 seconds, and then turn on and stay on. I've googled this, and
simulated the circuits that people have designed for this purpose, and
they don't seem to work. I know someone who tried actually making the
circuit and it still didn't work, so I think my simulation is correct.
Can anyone help?

Nick
 
J

John Fields

Jan 1, 1970
0
What I need is a simple circuit for a 5-10 second delay. No voltage
for 5-10 seconds, and then turn on and stay on. I've googled this, and
simulated the circuits that people have designed for this purpose, and
they don't seem to work. I know someone who tried actually making the
circuit and it still didn't work, so I think my simulation is correct.
Can anyone help?

---
Unless you've got some requirements you didn't mention, all you
really need is an RC driving a couple of Schmitt trigger inverters.

View in Courier:


+V>---> |
|
O
|
+-----+--------+
| | |
[R] | |
| | \ | \
+----| >O---O| >-->OUT
| | / | /
[C] | |
| | |
GND>----+-----+--------+
 
I

Ignoramus16588

Jan 1, 1970
0
What I need is a simple circuit for a 5-10 second delay. No voltage
for 5-10 seconds, and then turn on and stay on. I've googled this, and
simulated the circuits that people have designed for this purpose, and
they don't seem to work. I know someone who tried actually making the
circuit and it still didn't work, so I think my simulation is correct.
Can anyone help?

Unless you've got some requirements you didn't mention, all you
really need is an RC driving a couple of Schmitt trigger inverters.

View in Courier:


+V>---> |
|
O *<======
|
+-----+--------+
| | |
[R] | |
| | \ | \
+----| >O---O| >-->OUT
| | / | /
[C] | |
| | |
GND>----+-----+--------+

John, what does letter "O" (which I marked with *<=====) stand for?

Also, is that the kind of thing that resets itself when power is
removed?

thanks, your post was very educational for me.

i
 
G

gretsch27

Jan 1, 1970
0
unfortunately, I am an Aerospace Engineering major, and I'm not very
good with electronics. What is an RC or a Schmitt trigger? The
application is for a rocket timer. i am building a rocket engine, and
need to test it in a rocket. In order to recover it successfully, I
need a delay to trigger the parachute.

Thanks for your helps guys!

Nick
 
I

Ignoramus16588

Jan 1, 1970
0
unfortunately, I am an Aerospace Engineering major, and I'm not very
good with electronics. What is an RC or a Schmitt trigger? The
application is for a rocket timer. i am building a rocket engine, and
need to test it in a rocket. In order to recover it successfully, I
need a delay to trigger the parachute.

I have to wonder if a safer and more reliable way of triggering the
parachute would be to sense that your rocket is in free fall (no
gravity). That could be done with just a little weighted spring
contact. Make sure to wire in a safety switch that would allow this
circuit to work only if turned on, and turn it on before the launch.

Any thoughts?

i
 
L

Luhan

Jan 1, 1970
0
gretsch27 said:
unfortunately, I am an Aerospace Engineering major, and I'm not very
good with electronics. What is an RC or a Schmitt trigger? The
application is for a rocket timer. i am building a rocket engine, and
need to test it in a rocket. In order to recover it successfully, I
need a delay to trigger the parachute.

Apparantly "you don't have to be a rocket scientist" to be a rocket
scientist!

Luhan
 
M

martin griffith

Jan 1, 1970
0
What I need is a simple circuit for a 5-10 second delay. No voltage
for 5-10 seconds, and then turn on and stay on. I've googled this, and
simulated the circuits that people have designed for this purpose, and
they don't seem to work. I know someone who tried actually making the
circuit and it still didn't work, so I think my simulation is correct.
Can anyone help?

Nick
I think the problem could be with the high value of the timing
components, 100uF, 1Meg. ISTR having this problem years ago, there was
enough current leakage into pins 6 and 7 that prevented the capacitor
reaching the trigger voltage.

Try the CMOS version of the 555, or easier use John Fields approach


martin
 
J

John Fields

Jan 1, 1970
0
What I need is a simple circuit for a 5-10 second delay. No voltage
for 5-10 seconds, and then turn on and stay on. I've googled this, and
simulated the circuits that people have designed for this purpose, and
they don't seem to work. I know someone who tried actually making the
circuit and it still didn't work, so I think my simulation is correct.
Can anyone help?

Unless you've got some requirements you didn't mention, all you
really need is an RC driving a couple of Schmitt trigger inverters.

View in Courier:


+V>---> |
|
O *<======
|
+-----+--------+
| | |
[R] | |
| | \ | \
+----| >O---O| >-->OUT
| | / | /
[C] | |
| | |
GND>----+-----+--------+

John, what does letter "O" (which I marked with *<=====) stand for?
 
J

John Fields

Jan 1, 1970
0
unfortunately, I am an Aerospace Engineering major, and I'm not very
good with electronics. What is an RC or a Schmitt trigger? The
application is for a rocket timer. i am building a rocket engine, and
need to test it in a rocket. In order to recover it successfully, I
need a delay to trigger the parachute.

---
Well, in order to give you advice successfully we need to know some
more stuff, like, what battery voltage are you planning on using,
how does the parachute get triggered (that is, what do you need the
timer to do when it times out? Operate a relay or something like
that?) and how do you know when it's time to trigger the chute?
 
G

gretsch27

Jan 1, 1970
0
I'd like to use a timer because a simple acceleration switch would
trigger when the acceleration becomes negative, which is right after
the engine burns out. The rocket has to coast to get any altitude.
The burntime of the engine is only ~1 second. Flight time is around 20
seconds, so a 10 second delay would deploy the parachute shortly after
apogee. It seems easier to figure out the time to apogee. A magnetic
apogee detector is expensive, and a flight computer is more expensive,
and heavy. Timers are usually used as a backup system for rocket
recovery.

The ignitor for the ejection charge runs on 4 AA batteries in series.
To save weight, I'd like to use one of those little 12 volt batteries.
It looks just like an n-size, but it's not. I figure I will use that
12V battery to run the timer which will operate a relay to complete the
ignition circuit. Hopefully this is enough info.

Thanks for the help, and I apologize for being such a newb!
 
J

John Fields

Jan 1, 1970
0
The ignitor for the ejection charge runs on 4 AA batteries in series.
To save weight, I'd like to use one of those little 12 volt batteries.
It looks just like an n-size, but it's not. I figure I will use that
12V battery to run the timer which will operate a relay to complete the
ignition circuit. Hopefully this is enough info.

---
Almost! :)

How do you plan to start the timer, and will that little battery
supply enough current for the ignitor to work and hold in a relay at
the same time?

I guess the question is really "How much current does it take to
make the ignitor work?"
 
G

gretsch27

Jan 1, 1970
0
I was going to use 4 AA batteries for the ignitor. I'm not sure
exactly how much current the ignitor takes. I know that 2 AAs isn't
enough, but 4 works. The 12V battery will just have to keep the relay
closed so that the AAs trigger the ignitor. I'll probably start the
timer using a magnetic switch that disconnects from the rocket when it
takes off.
 
S

Sjouke Burry

Jan 1, 1970
0
gretsch27 said:
What I need is a simple circuit for a 5-10 second delay. No voltage
for 5-10 seconds, and then turn on and stay on. I've googled this, and
simulated the circuits that people have designed for this purpose, and
they don't seem to work. I know someone who tried actually making the
circuit and it still didn't work, so I think my simulation is correct.
Can anyone help?

Nick
8000.000 hits for google delay timer
 
J

John Fields

Jan 1, 1970
0
I was going to use 4 AA batteries for the ignitor. I'm not sure
exactly how much current the ignitor takes. I know that 2 AAs isn't
enough, but 4 works. The 12V battery will just have to keep the relay
closed so that the AAs trigger the ignitor. I'll probably start the
timer using a magnetic switch that disconnects from the rocket when it
takes off.

---
Great! I misread it and thought you were going to use the little
12V battery (I think it's called an A23 or something like that) to
trigger the ignitor.

I went to a few of the model rocketry sites on the web and looked up
ignitors, and it seems like they need 3 amps or so to fire, so the
relay needs to be able to handle _at least_ that.

Here's a simple circuit that simulates nicely:

..
.. +----+-----+---------+----------+--------+
.. | | | | |K | COM O-->TO +6
.. | +->[200K] | [1N4001] [COIL]- - -|
.. O | | C | | O--> |
.. |NO | 2N4403 B--[1K]--+--------+ |NO
.. O |S1 | E | +-------->TO IGNITOR
.. | | | |
.. |+ | [1K] |
..[12V] | | C
.. | +---------+-----------------B 2N4401
.. | | |+ E
.. | | O [1200µF] |
.. | NO| | |
.. | S2| O | |
.. | | | |
.. +----------+---------+-------------------+
..

It starts timing out when S2 is no longer held closed (by your
magnetic latch?) and allows the 1200µF cap to charge up (through the
200 kohm pot) to the point where the 2N4401 starts to conduct. That
will start to turn on the 2N4403 whichwill turn on the 2N4401 even
harder, which... So you get a quick snap-in of the relay.


Here's the LTSPICE circuit file:

Version 4
SHEET 1 1268 852
WIRE -464 272 -464 64
WIRE -464 624 -464 352
WIRE -400 528 -400 496
WIRE -400 624 -464 624
WIRE -400 624 -400 608
WIRE -272 496 -400 496
WIRE -272 624 -400 624
WIRE -272 624 -272 544
WIRE -224 480 -224 432
WIRE -224 624 -272 624
WIRE -224 624 -224 560
WIRE -112 64 -464 64
WIRE -112 272 -112 64
WIRE -112 432 -224 432
WIRE -112 432 -112 352
WIRE -112 480 -112 432
WIRE -112 624 -224 624
WIRE -112 624 -112 544
WIRE 16 64 -112 64
WIRE 16 160 16 64
WIRE 16 288 16 256
WIRE 16 432 -112 432
WIRE 16 432 16 368
WIRE 112 208 80 208
WIRE 272 64 16 64
WIRE 272 112 272 64
WIRE 272 208 192 208
WIRE 272 208 272 176
WIRE 304 432 16 432
WIRE 368 64 272 64
WIRE 368 96 368 64
WIRE 368 208 272 208
WIRE 368 208 368 176
WIRE 368 384 368 208
WIRE 368 624 -112 624
WIRE 368 624 368 480
WIRE 368 672 368 624
FLAG 368 672 0
SYMBOL pnp 80 256 R180
SYMATTR InstName Q1
SYMATTR Value 2N4403
SYMBOL npn 304 384 R0
SYMATTR InstName Q2
SYMATTR Value 2N4401
SYMBOL res -128 256 R0
SYMATTR InstName R1
SYMATTR Value 200k
SYMBOL cap -128 480 R0
SYMATTR InstName C1
SYMATTR Value 1200e-6
SYMBOL res 0 272 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res 208 192 R90
WINDOW 0 62 58 VBottom 0
WINDOW 3 64 54 VTop 0
SYMATTR InstName R3
SYMATTR Value 1k
SYMBOL voltage -464 256 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL voltage -400 512 R0
WINDOW 0 -53 5 Left 0
WINDOW 3 -242 110 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value PULSE(1 0 2 1E-6 1E-6)
SYMBOL sw -224 576 M180
WINDOW 0 32 15 Left 0
WINDOW 3 32 44 Left 0
SYMATTR InstName S2
SYMBOL ind 352 80 R0
SYMATTR InstName L1
SYMATTR Value 100e-3
SYMATTR SpiceLine Rser=240
SYMBOL diode 288 176 R180
WINDOW 0 24 72 Left 0
WINDOW 3 43 36 Left 0
SYMATTR InstName D1
SYMATTR Value 1N4148
TEXT -488 688 Left 0 !.model SW SW(Ron=1 Roff=10Meg Vt=0.5Vh=0)
TEXT -498 708 Left 0 !.tran 0 20 0
 
D

DaveM

Jan 1, 1970
0
gretsch27 said:
unfortunately, I am an Aerospace Engineering major, and I'm not very
good with electronics. What is an RC or a Schmitt trigger? The
application is for a rocket timer. i am building a rocket engine, and
need to test it in a rocket. In order to recover it successfully, I
need a delay to trigger the parachute.

Thanks for your helps guys!

Nick


Nick, according to the diagram you drew of -your- circuit, I see that the
voltmeter is connected from the 555 output pin (3) and the Trigger pin (2). Try
connecting it from pin 3 to circuit ground (Pin 1).
Also, pin 2 is the trigger input. You will need to simulate a negative-going
pulse on that pin to trigger the timer. A switch to ground on pin 2 should
work. I didn't check your values, but they look to be in the ballpark.
And make sure you're using the correct version of the 555 as specified by the
author of your test circuit. The CMOS version is different from the bipolar
version. Download the datasheets for each and use the one that's appropriate
for your parts bin. The datasheets will give you more diagrams and explanations
on how they work.

Cheers!!!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!
 
B

Ben Gustave

Jan 1, 1970
0
gretsch27 said:
What I need is a simple circuit for a 5-10 second delay. No voltage
for 5-10 seconds, and then turn on and stay on. I've googled this, and
simulated the circuits that people have designed for this purpose, and
they don't seem to work. I know someone who tried actually making the
circuit and it still didn't work, so I think my simulation is correct.
Can anyone help?

Nick

http://www.kpsec.freeuk.com/555timer.htm

Use the monostable design (like the one you posted) and then use the Schmitt
trigger (described at the end of the link) to invert the signal. For a
relay I'd use a low voltage power mosfet, but it's all up to you.

Ben
 
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