NOOB needs help.

[ThisIsMe]

Hi all,

In reading through here I see a lot of great advice so  I figure I would see if I could get some assistance on my little project here.  It has been decades since I have done much with circuits and my mind is a little vague in the area, so be gentle.

I have the following circuit.  In short it is just a 555 monostable circuit.  When the switch is closed I get a one second high from pin 3.  Works great.


Problem is the actual switching current (coming from the reverse switch of a car) is +12v.  More or less I need to trigger pin 2 (which needs to see a low) with a +12V.

I have tried a couple of transistors to trigger it.  I can get the transistor to work but it does not trigger the 555.

I guess you could say I am a little over my head at this point and I turn here for help.  I assume I am correct in getting a transistor to work is the best solution?  If so is there a circuit example available?  I have searched a lot for something similar and no luck.  I have tried a number of different switching transistor circuits all without luck.

Any advice would be appreciated. 

Thanks,
Chris

 

[audioguru2]

A transistor inverts the input easily like this:

 

[ThisIsMe]

Audio,

Well thanks that puts a little confidence into my problem as I had thought the same thing.  Scary as the image you created is almost exactly what I had put together and was having trouble with (see attached).  So at least I was on the right path.

Problem is it is not working.  Even more confusing for me is that say 1 in 10 times hitting the switch it will work.  No idea why.  I had tried using your resistor settings as well and no luck.  I know I am missing something simple.  The transistor is working as it should, just not triggering.

Where to look at next?

Thanks again for the help.

 

[ThisIsMe]

Well I figured out the problem on this one.  It was not with the circuit but with the Multisim simulator that I am still learning.  Seems that my time divider was set too high and the circuit was not working.  ??????  Got me.  Either way it does seem to be working.

Audio,  Thanks for the vote of confidence that I was doing the right thing, could not of figured out the problem was elsewhere without.

On a similar circuit I am having another problem (should be easier).  I have a 555 circuit that is powering a solenoid.  Switch needs to be held down for one second before the circuit will activate. 

I have the timing and circuit working fine.  Problem is that I am getting a spike on the initial switch contact then down to 0v until the one second timer is done and the circuit goes high again.  In vane I cannot get rid of the spike. 

 

[audioguru2]

Your switch should activate the input of the monostable timer. It is activating the power supply of the timer and when the power is turned on then the input capacitor triggers the timer because it holds pin 2 low for a moment.

R13 does nothing but drain the battery.