ON/OFF LED Circuit

[jdaniels]

Hello,
I need some help. I am really new to electronics and am hoping I can get some help with this problem. I am sure this will be an easy solution for someone else.

I am trying to come up with a 9V tester to do a quick check on a machine that I work with. The tester will get hooked up through a connector to receive open and closed contacts from the machine. No voltages are on the contacts. I have attached a basic layout of what I am brainstorming, but ran into some problems. I am trying to turn on a GREEN LED if a certain contact is closed and a RED LED if the same contact opens up. I have 3 signals I need to monitor in this way but the fourth is just a GREEN LED if the contact is closed.

My problem is that I can't get the LED's to alternately work. Basically flip flop and latch. I have been able to get the RED LED to come on if the contact is open using a transistor. But then, I cant figure out how to wire in the GREEN LED so when the contact closes it comes on and the RED LED turns off.

On the attached print, the switches are actually contacts from relays on the machine, but to simplify the print I just used switches.

Like I said I am really new to all of this and the print is just an idea I had. Maybe I am looking at this entirely the wrong way. Hopefully someone will be able to help me on this. I appreciate all the help I can get.

Thanks in advance.

 

[ericgibbs]

hi,
Do you mean something like this.??

 

[jdaniels]

Eric,
Thanks for the reply. Yes, I think that looks like something that might work. I will mess around with it and reply back. Thanks again.

 

[colin55]

The circuit above is way over-designed. All you need is this:
View attachment 64023

 

[ericgibbs]

The circuit above is way over-designed. All you need is this:

This what the OP asked for:>

I am trying to turn on a GREEN LED if a certain contact is closed and a RED LED if the same contact opens up. I have 3 signals I need to monitor in this way but the fourth is just a GREEN LED if the contact is closed.

In your version of the circuit you have crossed over the LED colours.!!

In my way over-designed circuit, it does what the OP asked for.

If you feel the need to answer an OP's question, read the question first.

 

[colin55]

Just change the LEDs and put another diode in series with the 1N4148. It's not rocket science.
It just doesn't need a transistor to do the trick.

 

[jdaniels]

Eric,
Thanks for the post. It works as advertised. I knew this would be an easy fix for you guys.

 

[jdaniels]

Colin,
I was able to get your circuit to work. I just had to swap the LEDs to get the colors right. I started with a transistor because I wasn't aware I could use a diode that way.

Thanks for all the help. I appreciate the look.