My 12V Signal To 0V -=- My 0V Signal to 12V

[iso9001]

I have a signal coming from a peice of equipment that when ON sends 12V to a computer and when off 'sends' 0V.

I replaced the equipment with a newer version that works the oposite way around. So that when ON is have a 0V signal and when OFF the signal is 12V

I can not modify either system. Only add somthing in between that will convert it to what I need.

What is the easiest way to take that 12V signal and make it 0V and when its at 0V make it 12V?

I know I can do this with a signal throw relay, but they are large and might not be the best way. Or maybe it is ?

 

[Optikon]

I have a signal coming from a peice of equipment that when ON sends 12V to a computer and when off 'sends' 0V.

I replaced the equipment with a newer version that works the oposite way around. So that when ON is have a 0V signal and when OFF the signal is 12V

I can not modify either system. Only add somthing in between that will convert it to what I need.

What is the easiest way to take that 12V signal and make it 0V and when its at 0V make it 12V?

I know I can do this with a signal throw relay, but they are large and might not be the best way. Or maybe it is ?

My first thought is use a transistor in common emitter configuration. This will invert your 12V signal. Also, don't be so quick to throw out relay idea.

Think about power & switching speed requirements this will determine the actual physical size of both the transistor and relay solution. If the speed is relatively slow and low power, one can obtain small relays comparable in size to common transistor packages.

Tell us, how fast does it need to do this switching and what kind of currents are involved?

 

[iso9001]

I'm not EXACTLY sure, but its operating a small solenoid/pump... so figure a high speed would be 30-50ms. I know a relay would work, I was just wondering it maybe there was a specific component for this or somthing,

Very small signal, a few mA. Just to make sure this thing is working or not.

Normal 30amp 12V relays cost $5 a pop, but I guess I could order in somthing smaller or maybe even solid state

 

[Roff]

You said in your first post that the signal goes to a computer. This should not be a high current load. You should be able to invert the signal with a 12 volt supply (battery or wall wart) and a CMOS Schmitt trigger (CD40106 or CD4093). Be sure to connect all unused input pins on the IC to GND. You could use a transistor instead, as Optikon suggested, but the CMOS inverter will not load your output.

 

[jbeng]

A LM311 voltage comparator circuit could be used for this application, or an optocoupler circuit (4N37 for example). Both would also require a power supply, like Ron H's suggestion.
JB

 

[iso9001]

opto-iso wha now... ? I think thats a little more work then a relay.

What are the pros/cons of a solid state vs mech relay anyway ?

 

[Roff]

opto-iso wha now... ? I think thats a little more work then a relay.

What are the pros/cons of a solid state vs mech relay anyway ?

I don't see any need for a relay. That's sorta like using a WWII tank to drive to the grocery store.
An optoisolator would be useful if you have a lot of electrical noise or separate ground references for the source and destination, but if it worked before, it seems like a simple inverter would work here.

 

[williB]

You said in your first post that the signal goes to a computer. This should not be a high current load. You should be able to invert the signal with a 12 volt supply (battery or wall wart) and a CMOS Schmitt trigger (CD40106 or CD4093). Be sure to connect all unused input pins on the IC to GND. You could use a transistor instead, as Optikon suggested, but the CMOS inverter will not load your output.

That would be my suggestion Ron..
exactly a cmos inverter with schmitt trigger inputs