Hi,
I need a 12 pulse every time 12v comes on,
for a friends car im looking at,
when you unlock the cars 12 volts stay on and when you lock the car the 12 volts swap over to the lock wire, now i need a pulse each time the power swaps over, i have looked into the 555 timer but i cant work out how to get a pulse, I am using a program "ciruit wizard"
any help would be great.

 

planty,

Attached is a circuit that I helped a student with, to detect the daily activity of 3mm blind cave fish. The input has been modified to detect positive going 12v levels...as in your lock system. I think this will do it.

Ken

Attached Images

Change Detector.gif (26.0 KB, 12 views)

__________________
"To invent, you need a good imagination and a pile of junk."
Thomas A. Edison (1847 - 1931)

 

Thanks for that, but thats a bit much i think, just a basic kit
when i recive 12volts i just need a pulse.
Then i can just make another one for the other lock...

 

Hi Planty,

Is this simple enough ?

on1aag.

Attached Images

	Pulse schematic.PNG (13.5 KB, 16 views)
	Pulse.PNG (13.7 KB, 9 views)

 

OK...a little less complicated. RA and CA can be paralleled with as many lock/unlock inputs (RB/CB, RC/CC....RX/CX) as needed. Whenever one lock/unlock changes there is a fixed width pulse out of the 555. Or, if you don't care about the output pulse width...there is one without the 555 monostable.

Ken

Attached Images

	Change Detector2.gif (16.2 KB, 9 views)
	Change Detector3.gif (10.8 KB, 10 views)

__________________
"To invent, you need a good imagination and a pile of junk."
Thomas A. Edison (1847 - 1931)

 

looks easy, what is that bs250, u1?

 

That look easy ish, but what is that 2n3904 - Q1 thing?

 

It's a common NPN transistor.

__________________
Bill
Smart Kits build Smart People
http://www.blueroomelectronics.com

 

on1agg,

Could you complete your schematic with two inputs, one from a 12v locK wire and one from a 12V unlock wire, as in planty's original description. Lock is always high or unlock is always high, and with positive output pulse as in your signal display for the "change over". I might be just missing something in your approach.

planty:
And not knowing what you are going to do with the 12v pulse...one more with even less.

Ken

Attached Images

Change Detector4.gif (5.9 KB, 5 views)

__________________
"To invent, you need a good imagination and a pile of junk."
Thomas A. Edison (1847 - 1931)

 

just made this up and no power goes past the resistors or the capacitors
try the other one now

 

Thanks for that, my circuit wizard has that, i might know what they are if i saw them.
Thanks

 

just made this one up also and the same thing, no power get past the resistors or the caps..

 

Hi Planty,

O.K. now it's stereo !

on1aag.

Attached Images

	Pulse schematic 2.PNG (15.9 KB, 17 views)
	Pulse 2.PNG (13.7 KB, 15 views)

 

O.M.G. will give this a go in a sec

 

well this one works now. it help if i put power to no.4, i think i need a bit longer time on the pulse. i will have a play,