UdderlyOffroad Posted March 13, 2012 Share Posted March 13, 2012 As the subject line really…Is anyone aware of a discrete, ready-built unit that would operate as an AND gate, but with 12v? I have tried to google this, but 1) Google does boolean search-strings (kinda) and 2) search for 12v Gates produces gates of the common or garden-variety! I know I could use a relay as described in the picture below, and probably will be what I end up doing, but I was just wondering if anyone had an off-the-shelf solution? Matt Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted March 13, 2012 Share Posted March 13, 2012 CMOS will work for you http://www.nxp.com/d...et/HEF4081B.pdf however it really depends what you are doing and the relay may work better for you. EDIT: oops just noticed you said ready built, sorry. You could use a solid state relay if you felt like it ... wouldn't click then Quote Link to comment Share on other sites More sharing options...
simonr Posted March 13, 2012 Share Posted March 13, 2012 Any CMOS chip will operate on 12v. AND gates are rarely used however. Instead you use NAND (Not AND) where the output is inverted. To implement an AND gate, use a second NAND gate with both inputs connected together - which will invert the output of the first gate giving you a logical AND function. The relay is simpler though. Si Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted March 13, 2012 Share Posted March 13, 2012 Oh and a tip for googling would be to look for 'Logic Gates' instead of 'AND Gates', they tend to be in families anyway so once you find one of the right type the one you are after won't be far away Quote Link to comment Share on other sites More sharing options...
HoSS Posted March 13, 2012 Share Posted March 13, 2012 What's simpler or more off-the-shelf than the relay?! Its exactly what i have done on my truck. Have 12V and 24V circuits,both with battery isolators, so to avoid damage to either altenator, this relay will not let me start the engine unless both 12v AND 24v isolators are in. Quote Link to comment Share on other sites More sharing options...
UdderlyOffroad Posted March 13, 2012 Author Share Posted March 13, 2012 Oh and a tip for googling would be to look for 'Logic Gates' instead of 'AND Gates', they tend to be in families anyway so once you find one of the right type the one you are after won't be far away Facepalm! I knew that...honest Any CMOS chip will operate on 12v. AND gates are rarely used however. Instead you use NAND (Not AND) where the output is inverted. To implement an AND gate, use a second NAND gate with both inputs connected together - which will invert the output of the first gate giving you a logical AND function. The relay is simpler though. Si What's simpler or more off-the-shelf than the relay?! Thanks guys, you are both correct of course...I just wanted to ask in case I'd missed a trick. But yes a relay will be much quicker than soldering CMOS chips onto breadboard and heatshrink-wrapping the resultant assembly. Fortunately all I'm driving off this circuit is an LED. M Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted March 13, 2012 Share Posted March 13, 2012 What are you trying to achieve? If you need an LED to light when two things BOTH happen, perhaps one of them could work on the ground side of the LED instead and hence no gate needed. Also try googling "relay logic", "transistor logic" for how-to's on making gates with discrete components. Quote Link to comment Share on other sites More sharing options...
HoSS Posted March 14, 2012 Share Posted March 14, 2012 well, if its just for an led you could do it with 2 transistors, and 3 resistors... but thats some soldering. Still think a small relay is the most 'off the shelf' and robust solution. Quote Link to comment Share on other sites More sharing options...
MrKev Posted March 14, 2012 Share Posted March 14, 2012 As the subject line really…Is anyone aware of a discrete, ready-built unit that would operate as an AND gate, but with 12v? Any CMOS chip will operate on 12v When you say 12V, do you really mean "from a vehicle's supply"? There's quite a difference between an nice clean 12V regulated supply, and vehicle electrics. Expect to see lots of spikes due to changes in alternator loading, windscreen wiper motors, plus voltage depression during cranking, and so on. I wouldn't want to run a CMOS device directly from the vehicle without some protection. As others have said, particularly if this is a vehicle application - use a relay! Kev Quote Link to comment Share on other sites More sharing options...
simonr Posted March 14, 2012 Share Posted March 14, 2012 When you say 12V, do you really mean "from a vehicle's supply"? More or less - at least in this case. If it's just as an indicator - one LED lighting when two inputs are high then the odd spike or noise are not going to make much difference - the LED might flash briefly occasionally. The point was more that CMOS will be happy at the 12v to 15v you are likely to see - and unlikely to spontaneously die as a result of transient spikes. It is however crazy not to de-couple the power supply to the chip - for sake of a couple of Capacitors. If the circuit were being used as part of a finite state machine controlling something more critical - then yes, you would need to bomb proof the power supply. However, it's still often useful to have it operate on 12v rather than 5v. Si Quote Link to comment Share on other sites More sharing options...
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