555 Timer Circuit Short pulse Help

Dodgydave

Joined Jun 22, 2012
8,473
Have looked into the extra switches and you're going to have to make a transistor for each switch, like in post#88, this will make sure it pulses in the Off position,

The drawing you made in post#101 wont pulse in the centre position for the second switch as its not got a transistor to it.


Also the diode that Scott was on about goes across the 1meg resistor on pins 4,8 its to discharge the the 1uF capacitor faster on pin 4.

Hope thats clear to you?
 
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ScottWang

Joined Aug 23, 2012
6,834
Have looked into the extra switches and you're going to have to make a timer with transistor for each switch, like in post#88, this will make sure it pulses in the Off position,

The drawing you made in post#101 wont pulse in the centre position for the second switch as its not got a transistor to it.

Also the diode that Scott was on about goes across the 1meg resistor on pins 4,8 its to discharge the the 1uF capacitor faster on pin 4.
If the RC on Pin 4 were useless then it can be take away and just connecting pin 4 to+12V.
 

Thread Starter

Michael Knight

Joined Nov 5, 2015
90
DTMF_PulseForDPDT_RockersAddingOtherRockersTheory_LR.jpg

All good points guys, Yes the power up pulse was an issue naturally because I would not want a pulse sent just by the simple act of starting the car. About a few seconds or so should be ample enough time to start the car before wanting to go about pressing any buttons so even 5 or so seconds to discharge the caps in the circuit would be I would think more than enough.

OK so then, does this look like it should be OK?
I think I'm not understanding the placement of D7 & D6 though? So another visual there would help ;)
 

Thread Starter

Michael Knight

Joined Nov 5, 2015
90
I said take away because the TS said it didn't work, and if he didn't care about the time, even the parts D6 and R9 also can be take away, less parts less problem.
No no, I must have not been clear, sorry about that, it did work, but what I was doing was plugging back in the power supply too fast, I found if I waited a short time and plugged it back in then the pulse was NOT sent on power up.
Sorry I must not have been clear enough ;)
 

Dodgydave

Joined Jun 22, 2012
8,473
Mike, this is what you need for each rocker switch, like this

DSC_0042.JPG


Thats one transistor, 3 diodes,100k resistor, 10k resistor, 1meg resistor and pulse cap,.

Also this is where the diode D6 should be, its to discharge the cap on power down.

DSC_0047.JPG
 
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ScottWang

Joined Aug 23, 2012
6,834
No no, I must have not been clear, sorry about that, it did work, but what I was doing was plugging back in the power supply too fast, I found if I waited a short time and plugged it back in then the pulse was NOT sent on power up.
Sorry I must not have been clear enough ;)
Then if you take that RC away and connecting pin 4 to +12V, and try to waiting for 5~6 seconds as you did, when you power up again to see does it has the pulse appear again?
 
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