How do I make ne555 work only once?

Thread Starter

하용우 (하랩)

Joined Jan 23, 2019
1
Hi.
I attached ne555 circuit.

I push 2pin switch, There is output on 3pin and stop output.
If I push switch again, ne555 works agian.
But I want to make ne555 work for the first time.

Is it possible??
 

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crutschow

Joined Mar 14, 2008
24,350
Sorry, I don't understand.

What is 2pin and 3pin?

What do you mean "make ne555 work for the first time"?

What exactly is the purpose of the circuit?
 
Last edited:

jpanhalt

Joined Jan 18, 2008
8,734
Motor control circuits often have a push button switch to turn on and another button switch to turn off. When on, current to a relay coil through the NO contacts keeps them on. The only way to tun them off is to interrupt that current. You could apply that principle to your problem:

1579756320312.png

Once that relay is activated by the 555, the normally open contacts (NO) will stay closed and the relay energized until you remove or interrupt the the power. There are variations on that design. That is just one.
 

crutschow

Joined Mar 14, 2008
24,350
He probably wants the 555 to work ONLY for the first time.
If that's what you want, then remove the connection to pin 7 and connect a small diode (e.g. 1N4148) across the 100kΩ resistor (anode towards pin 6).
Then you will have to momentarily remove the power before the 555 will retrigger.
 

ci139

Joined Jul 11, 2016
1,187
there could be an option that the device will cycle once if the power is turned on and further triggering is done by a button?
 

eetech00

Joined Jun 8, 2013
1,836
Hi.
I attached ne555 circuit.

I push 2pin switch, There is output on 3pin and stop output.
If I push switch again, ne555 works agian.
But I want to make ne555 work for the first time.

Is it possible??
Hello,
I think you want it to time out only once no matter how many times the PB is pressed(?).

Here's one way to do that:
The circuit below disables the pushbutton after it is pressed once and timing begins.
You'll need to test on breadboard (I didn't).

eT

1579813048248.png
 

crutschow

Joined Mar 14, 2008
24,350
The circuit below disables the pushbutton after it is pressed once and timing begins.
Yes, I just realized that my simple modification will cause the output to go high whenever the TRIG input is low, even though it won't stay high after the TRIG input goes high, so the trigger input needs to be disabled after the first pulse.
That could also be done with a second 555 used as a latch.
 

ci139

Joined Jul 11, 2016
1,187
NE555.gifTLC555.gif
••• if you want the first cycle to be triggered by the event "POWER ON" -- it might occur so simultaneously - because the timing capacitor has no charge and if the internal trigger "boots" to ON state the OUTP will be high until reset by increasing capacitor voltage
if it does not simultaneously "trigger" at startup you should keep the RESET (p4) LOW by RC chain and send a LOW pulse to the TRIGGER (P2) ← the least is done by another startup RC timing chain at the input of extra inverting buffer and the output differentiator + reverse diode to (p2)
, or less certain and more noise prone as below
Misc - 555 - TEST - 2.png

••• if you want that the TRIGGER (p2) has a response only at the first time it's pressed -- there are variety of ways to implement such . . .
one way is to use RS LATCH and a MOS-Fet that will disable ground from the trigger button after the OUTP (p3) goes high
, etc. ...
1579898575723.png
 
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ci139

Joined Jul 11, 2016
1,187
Since the TS hasn't been back since his original post, we may be just spinning our wheels.
i don't have a problem with that . . . if there's nothing to do just start a linear voltage regulator or reference or CC or SMPS design from scratch and see what's coming out of that . . . if you just wait - nothing happens
 
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