power on delay using a 555 chip

[[email protected]]

Hello,

Is it possible to give a delay of 20mins upon power on before a LM555
can be used as a oscillator in its astable mode? I am designing a
circuit which has to follow this sequence: -
step1: On application of power to the 555 its output should be 0volts
step2: Upon completion of 20mins the 555 should start to give pulses at
its output.
step3: On completion of 20mins the output of the 555 is given to the
gate of a triac to fire it up.

thanks is advance.

 

[Tom Biasi]

Hello,

Is it possible to give a delay of 20mins upon power on before a LM555
can be used as a oscillator in its astable mode? I am designing a
circuit which has to follow this sequence: -
step1: On application of power to the 555 its output should be 0volts
step2: Upon completion of 20mins the 555 should start to give pulses at
its output.
step3: On completion of 20mins the output of the 555 is given to the
gate of a triac to fire it up.

thanks is advance.

Might be easier to just use two 555s. One to trigger the other after 20
minutes and the triggered one to send the pulses.
Both these circuits are in the app notes.
Tom

 

[kfel]

are they in the app notes of LM555 from STMicro?

 

[default]

are they in the app notes of LM555 from STMicro?

There are whole sites devoted to novel ways to use the 555. Try
google

 

[John Fields]

are they in the app notes of LM555 from STMicro?

---
1. Why don't you do your own legwork?

2. 20 minutes is quite a long time for a 555. How accurate
do you need the 20 minute timeout to be?

3. Once the pulses have started, how long do you want them
to continue?

4. Please bottom post.

 

[kfel]

Accuracy within +10% to -10%. Once the pulsing has started it should
continue till mains is disconnected.

 

[John Fields]

Accuracy within +10% to -10%. Once the pulsing has started it should
continue till mains is disconnected.

---
I've rearranged your post to give you an example of what bottom
posting looks like. Also, you may want to read:

http://groups.google.com/support/bin/answer.py?answer=12348&topic=250

Particularly:

"Summarize what you're following up.

When you click "Reply" under "show options" to follow up an existing
article, Google Groups includes the full article in quotes, with the
cursor at the top of the article. Tempting though it is to just
start
typing your message, please STOP and do two things first.
Look at the quoted text and remove parts that are irrelevant.
Then, go to the BOTTOM of the article and start typing there.
Doing this makes it much easier for your readers to get through your
post. They'll have a reminder of the relevant text before your
comment, but won't have to re-read the entire article.
And if your reply appears on a site before the original article
does,
they'll get the gist of what you're talking about."



If you bottom post I'll help you. If you don't, I won't.

 

[kfel]

2. 20 minutes is quite a long time for a 555. How accurate
Accuracy within +10% to -10%.

Once the pulsing has started it should continue till mains is
disconnected.

 

[Chris]

Hello,

Is it possible to give a delay of 20mins upon power on before a LM555
can be used as a oscillator in its astable mode? I am designing a
circuit which has to follow this sequence: -
step1: On application of power to the 555 its output should be 0volts
step2: Upon completion of 20mins the 555 should start to give pulses at
its output.
step3: On completion of 20mins the output of the 555 is given to the
gate of a triac to fire it up.

thanks is advance.

Hi, Kfel. From your earlier conversation, possibly this might fill the
bill (view in fixed font or M$ Notepad):

|
| VCC .--------------------.
| + | |
| 16| | VCC VCC |
| VCC .--o---------------------. | + + |
| + | Vdd | | | | |
| |.01uF | | | .-. .--o--o--.
| --- | | | | | | 8 4 |
| --- | |3 | | | | RST |
| | 12| CD4060 Q14o---o '-' | |
| o-------oRST | | | | | To
| | | | | o----o7 |Triac
| .-. | | .-. | | 3o-->
| | |10K | | | | .-. | 555 |
| | | | Vss | | |15K | | | |
| '-' '--o----o-----o------o---' '-' | | .-o6 |
| | 8| 11| 10| 9| | '-' | | |
| === === .-. .-. | | | | | |
| GND GND | | | |56K | V o--o-o2 |
| | | | | | - | | 1 5 |
| '-' '-' | 1N914| --- '--o--o--'
| | | | | --- |
| | .-. | | | ===
| | .->| |100K | | === GND
| | | | | | | GND
| | | '-' | |
| | | | || | |
| '-o---o--||--' |
| | ||1uF |
| '--------------'
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Sorry you can't do this with a 555 alone, but 20 minutes is just too
long for +/-10% accuracy. As an alternative, try the CMOS CD4060 along
with your 555. The 4060 kind of revolutionized industrial time delay
relays back when the earth's crust was cooling, and it can work fairly
well for your application, too. Look at the data sheet for reference:

http://www.fairchildsemi.com/ds/CD/CD4060BC.pdf

Internal to the 4060 is the makings of an internal oscillator, which
can be set up either with a crystal or an R-C network. The components
above are chosen so it will oscillate at between 3Hz and 9Hz, depending
on the pot setting. You'll have to tweak it in, because the frequency
of oscillation is somewhat dependent on power supply voltage (you do
have a well-regulated DC power supply between +5V and +15V here,
right?). Look at one of the intermediate outputs, and tweak it in with
a frequency counter if you want exact results.

The thing is, to get +/-10% repeatability, you'll need a cap that can
do that. Your repeatability is going to be almost entirely dependent
on your cap. I'd look at mylar or one of the polys -- stay away from
electrolytics and tantalums.

Anyway, after 20 minutes, the Q14 output will go high. That will
forward bias the diode, pumping current into the summing junction and
swamping out the oscillations. The 4060 will stay stuck until you
cycle power, which is what you want. It also puts the RST input of
your 555 high, allowing it to oscillate, and drive your triac as
requested.

By the way, as a simple precaution, make sure the 1N914 is shielded
from light if it's got a glass case. Light will mess up the diode
leakage current.

Would you like fries with that?

Cheers
Chris

 

[kfel]

Thanks a million chris. Will try it out.

 

[Chris]

Thanks a million chris. Will try it out.

Trust, but verify. The circuit should work at any 555 supply voltage
(5 to 15VDC), but make sure it's regulated. Check the math for choice
of Rs and C ( f = 1/(2.2 * R1 * C) ). The R2 (coming off pin 11)
should be 330K or so. The diode and 15K resistor business is an
example of the time-honored MML logic family (Mickey Mouse Logic) --
great for hobbyists, kind of something to be embarassed about if you're
actually getting paid. It should work, though. You may want to
consider using a spare gate or something if someone's looking over your
shoulder, or inhibit the oscillator in another way.

Either that, or just brazen it out -- grin and say, "Well, it works,
doesn't it? Haven't you ever heard of Wired-OR?" ;-)

Cheers
Chris

 

[kfel]

Chris, I did try out the circuit but went about the testing in a phased
manner.
Step 1:
I rigged up the 555 in astable mode. Provided it with supply from a 9V
battery. Checked the output pin for oscillation and found it to be ok.
Step 2:
Then I rigged up a simple DC supply circuit using a 5.2V zener in
parallel with a 470uF/16V capacitor. (This circuit is explained in the
application note 954A of microchip corporation). Using this as the
primary source of the power to the 555 i checked the output pin for
oscillations and found it to be ok.
Step 3:
Rigged up a circuit containing of a 40W GLS lamp in series with triac
BT06600 from ST Micro. Connected one end of the lamp to the MT2
terminal. Other end of the lamp was connected to Phase (240Volts AC
RMS). MT1 terminal was connected to Neutral. Connected a wire from gate
terminal but did not connect it to the output of the 555 as yet.
Step 4:
Switched on the power supply and checked the output at pin 3 of 555 and
found it to be ok. As the gate terminal was not connected the lamp did
not glow. Now when i connected the gate terminal to the output of the
timer the 555 went kaboom. So did the triac. Unable to understand what
went wrong. Any help would be appreciated.

 

[John Fields]

Chris, I did try out the circuit but went about the testing in a phased
manner.
Step 1:
I rigged up the 555 in astable mode. Provided it with supply from a 9V
battery. Checked the output pin for oscillation and found it to be ok.
Step 2:
Then I rigged up a simple DC supply circuit using a 5.2V zener in
parallel with a 470uF/16V capacitor. (This circuit is explained in the
application note 954A of microchip corporation). Using this as the
primary source of the power to the 555 i checked the output pin for
oscillations and found it to be ok.
Step 3:
Rigged up a circuit containing of a 40W GLS lamp in series with triac
BT06600 from ST Micro. Connected one end of the lamp to the MT2
terminal. Other end of the lamp was connected to Phase (240Volts AC
RMS). MT1 terminal was connected to Neutral. Connected a wire from gate
terminal but did not connect it to the output of the 555 as yet.
Step 4:
Switched on the power supply and checked the output at pin 3 of 555 and
found it to be ok. As the gate terminal was not connected the lamp did
not glow. Now when i connected the gate terminal to the output of the
timer the 555 went kaboom. So did the triac. Unable to understand what
went wrong. Any help would be appreciated.

If you wired the power supply like Microchip shows on their
application note, you're lucky you're still alive. Notice that the
output of their supply is connected directly to mains HOT, so with
your TRIAC's MT1 connected to NEUTRAL, as soon as you connected the
wire from the 555 to the gate you were connecting mains HOT (through
the 555) to the gate, and then to NEUTRAL. Kaboom is right!

 

[Chris]

Chris, I did try out the circuit but went about the testing in a phased
manner.
Step 1:
I rigged up the 555 in astable mode. Provided it with supply from a 9V
battery. Checked the output pin for oscillation and found it to be ok.
Step 2:
Then I rigged up a simple DC supply circuit using a 5.2V zener in
parallel with a 470uF/16V capacitor. (This circuit is explained in the
application note 954A of microchip corporation). Using this as the
primary source of the power to the 555 i checked the output pin for
oscillations and found it to be ok.
Step 3:
Rigged up a circuit containing of a 40W GLS lamp in series with triac
BT06600 from ST Micro. Connected one end of the lamp to the MT2
terminal. Other end of the lamp was connected to Phase (240Volts AC
RMS). MT1 terminal was connected to Neutral. Connected a wire from gate
terminal but did not connect it to the output of the 555 as yet.
Step 4:
Switched on the power supply and checked the output at pin 3 of 555 and
found it to be ok. As the gate terminal was not connected the lamp did
not glow. Now when i connected the gate terminal to the output of the
timer the 555 went kaboom. So did the triac. Unable to understand what
went wrong. Any help would be appreciated.

Hi, Kfel. Sorry for your troubles.

The consensus of this group over time has been that the transformerless
power supplies shown in the Microchip appnote are not suitable for
anyone who asks for advice from this group.

Mr. Fields was kind enough to mention why your 555 blew up. Your
circuit common in Fig. 10, 11 and 12 are not at the same potential as
neutral. For Fig. 12, it's a long ways away!

I'd like to add that there are any number of other ways to do this
which don't involve putting your circuit at line voltage potential.
First, your 555 can drive a small relay directly, or it can drive an
NPN transistor which can switch the relay coil. If you're not
interested in a relay, you can use an optotriac IC to drive your triac.
If you want an authentic '70s feel to your circuit, you might have
your 555 drive the reset pin of another 555, which drives a pulse
transformer. The pulse transformer output can easily drive a sensitive
or non-sensitive gate triac or SCR.

The common element to all of these is that you're using an isolated
power source for fun and safety. A throwaway wall wart should me more
than sufficient, if you provide a voltage regulator of any kind that
can handle the current of your circuit.

If you'd like advice on any of these, feel free to ask.

Play safe, and have fun.
Chris

 

[kfel]

Chris,

The interesting part is that when i connected the output of the power
supply (using microchip's design) via a 3K9/2W resistor to the gate of
the triac (bypassing the 555 altogether) it worked perfectly. Is it
that i should have connected some resistance in series (say 820ohms)
with the output from the 555 before applying it to the triac?

 

[Chris]

Chris,

The interesting part is that when i connected the output of the power
supply (using microchip's design) via a 3K9/2W resistor to the gate of
the triac (bypassing the 555 altogether) it worked perfectly. Is it
that i should have connected some resistance in series (say 820ohms)
with the output from the 555 before applying it to the triac?

No, sorry, Kfel. I guess I wasn't being clear.

You *SHOULD NOT* use the transformerless power supply shown in the
Microchip appnote. I'm not giving advice on what is a ultra-cheap,
lazy and potentially hazardous way to power a circuit.

I'm not saying it's not done. But for a newbie (note your first
question), this type of power is too dangerous. If you want to talk
about any other option, go ahead. But I can't help you here.

If you want to talk about turning on line voltage stufff, get a wall
wart first so you have an isolated power supply. But I'm not going to
give advice on something that could potentially cause you injury.
Believe me, nothing personal at all. Just safety first here. Sorry.

Good luck
Chris