# 555 Timer Circuit Short pulse Help

#### Michael Knight

Joined Nov 5, 2015
90
OK here is a video demo to try and best explain what it is I am trying to do here.

#### Michael Knight

Joined Nov 5, 2015
90
Yes, i think your getting us confused here,

Do you want to trigger the timer when the rocker is pressed, and again when the rocker is released?
OK video is up, you might have to check my last post

#### Dodgydave

Joined Jun 22, 2012
9,443
Ok, rocker switch to the right, pulse timer, rocker switch in centre pulse timer, rocker switch to the left no pulse, yes or no?

#### Michael Knight

Joined Nov 5, 2015
90
Ok, rocker switch to the right, pulse timer, rocker switch in centre pulse timer, rocker switch to the left no pulse, yes or no?
Simple answer is "No" As in left also NEEDs a pulse, All three switch states need a pulse.
Rocker switch to middle (off) = Pulse
Rocker switch to left Device 1 (on) = Pulse
Rocker switch to right Device 2 (on) = Pulse

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#### Michael Knight

Joined Nov 5, 2015
90

I wonder if something like this will work? I found this circuit on Google that has an indicator state for output state High and Low. My thought was that perhaps the two states could be sent to our other "Timed" 555 circuit via the trigger input of this circuit from the rocker switches.??

This is the image I found online:

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#### marcf

Joined Dec 29, 2014
260
But do you know if there is a way for the latching switches to also generate a pulse through the timer when they are switched off?
Or is that so complicated it would not be worth the time?
Try this in the 'BU' mode.

#### Attachments

• 33.9 KB Views: 4

#### ScottWang

Joined Aug 23, 2012
6,933
View attachment 94289
I wonder if something like this will work? I found this circuit on Google that has an indicator state for output state High and Low. My thought was that perhaps the two states could be sent to our other "Timed" 555 circuit via the trigger input of this circuit from the rocker switches.??

This is the image I found online:
Before you connecting the LED to the pin 3 , you should test that two R and two LEDs independently to make sure they won't light up when the power is upper than 9V, if they light up then you better in series with a diode for each LED and recalculate the values of R.

#### Michael Knight

Joined Nov 5, 2015
90
Try this in the 'BU' mode.
Thanks macf, but I would need this explained in a lot more detail in order for me to understand what it is and how it works, and how I would implement it into my scenario.

#### Michael Knight

Joined Nov 5, 2015
90
Before you connecting the LED to the pin 3 , you should test that two R and two LEDs independently to make sure they won't light up when the power is upper than 9V, if they light up then you better in series with a diode for each LED and recalculate the values of R.
I did test out this circuit on it's own just wired to a 9V battery, I used a couple of 470R resistors for the two "R" resistors and the circuit works.
What I'm wondering is if it is possible to somehow use the two different LED states for pin 3 being either High or Low to send out to another timer circuit, (the one we have already worked out that sends the needed short pulse.) and have that generate the pulse for when my latching switches are in their "OFF" position.

#### Dodgydave

Joined Jun 22, 2012
9,443
Ok mike, try this circuit, extra diodes, resistors, and a transistor.

With the switch in either left or right position you get your pulse from the capacitors as normal, when the switch is in the off state ( centre) the two diodes Da and DB wont conduct and the transistor will turn on via Rc and Dc, and will give a pulse to the555 timer.

#### ScottWang

Joined Aug 23, 2012
6,933
Ok mike, try this circuit, extra diodes, resistors, and a transistor.

View attachment 94318

With the switch in either left or right position you get your pulse from the capacitors as normal, when the switch is in the off state ( centre) the two diodes Da and DB wont conduct and the transistor will turn on via Rc and Dc, and will give a pulse to the555 timer.
Please don't forget to cut and compress to as 800x600, I already did this for you, next time don't forget again, thanks.

#### Michael Knight

Joined Nov 5, 2015
90
Ok mike, try this circuit, extra diodes, resistors, and a transistor.

View attachment 94318

With the switch in either left or right position you get your pulse from the capacitors as normal, when the switch is in the off state ( centre) the two diodes Da and DB wont conduct and the transistor will turn on via Rc and Dc, and will give a pulse to the555 timer.
Thanks Dodgy dave, this one looks doable only I'm unclear on a few things in your diagram, I redrew it a little more clearly with some "?" marks.

Mod edit:
You still not to compress to 800x600.
I compressed it from about 1.3Mb to 48Kb, it is close to 26:1.

#### Michael Knight

Joined Nov 5, 2015
90
Dodgydaves last post looks really promising, I'm so going to try that today and post my results.... in the mean time I was also wondering about something like this?:

#### Dodgydave

Joined Jun 22, 2012
9,443
No you have missed out Rc, and its pin 1 that goes to negative supply not pin 4, look at my drawing.

#### Michael Knight

Joined Nov 5, 2015
90
No you have missed out Rc, and its pin 1 that goes to negative supply not pin 4, look at my drawing.
I'll try making a much clearer one in photoshop just to make sure I have it correct, but this looks very promising dodglydave

#### Michael Knight

Joined Nov 5, 2015
90
No you have missed out Rc, and its pin 1 that goes to negative supply not pin 4, look at my drawing.
OK I did a more cleaned up version but I'm sure I'm missing a few things so if you could kind of fill in the blanks that would be awesome.... just incase I have it wrong or have missed something.

#### Dodgydave

Joined Jun 22, 2012
9,443
The circuit is correct upto pin 2 of the 555 timer,

then you need to have your timing resistor and capacitor on pins 6,7 as normal, supply pins 4,8 to positive, pin1 to negative, output on pin 3.

#### Michael Knight

Joined Nov 5, 2015
90
The circuit is correct upto pin 2 of the 555 timer,

then you need to have your timing resistor and capacitor on pins 6,7 as normal, supply pins 4,8 to positive, pin1 to negative, output on pin 3.
Awesome Dodgydave, Take a look at this and see if it looks OK, if it all looks good then I can test this out and post a video with the results.
I think my timing 1M was lower i'll have to look at what I have on the breadboard

#### Dodgydave

Joined Jun 22, 2012
9,443
Connect pin 4 to pin 8, and its perfect.

#### ScottWang

Joined Aug 23, 2012
6,933
Awesome Dodgydave, Take a look at this and see if it looks OK, if it all looks good then I can test this out and post a video with the results.
I think my timing 1M was lower i'll have to look at what I have on the breadboard

View attachment 94333
Why you need that bjt stage for?