Guest shaner74 Posted January 10, 2005 Share Posted January 10, 2005 Hi, wondering if someone can help me figure out a problem? I want to kick on a warning light based on resistance measured between a pressure sensor and ground. This is a 12v DC system. At pressure goes down, resistance goes up and visa versa. So, at 3psi resistance is 300ohms, at 10psi resistance is 80ohms. A gauge interprets this and displays the correct pressure, but I really need a warning light too. How could I trigger a warning light at 3psi(300ohms)? Thanks! Link to comment Share on other sites More sharing options...
5614 Posted January 10, 2005 Share Posted January 10, 2005 by the sounds of it what you want to look into is the 741 op amp ICC. it's one of those black chips that you often see in electronics, theyre not very hard to wire in. Link to comment Share on other sites More sharing options...
The Rebel Posted January 10, 2005 Share Posted January 10, 2005 Hi, wondering if someone can help me figure out a problem? I want to kick on a warning light based on resistance measured between a pressure sensor and ground. This is a 12v DC system. At pressure goes down, resistance goes up and visa versa. So, at 3psi resistance is 300ohms, at 10psi resistance is 80ohms. A gauge interprets this and displays the correct pressure, but I really need a warning light too. How could I trigger a warning light at 3psi(300ohms)? Thanks! Probably loads of ways, depending what you got around you, the characteristics of the pressure sensor, and what circuitry is already in place (i.e. the guage). The easiest way is probably to put the pressure into part of a potential divider that feeds a transistor (BC109 will do). This in turn will act as part of a second pontential divider which will feed a second BC109 (through a 1k bias resistor) for the warning light. You could also put it into a wheatstone bridge with an op-amp. The op-amp doesn't have to be anything special if its just a warning light. Or you could use the resistance as part of an opamp circuit. Link to comment Share on other sites More sharing options...
ed84c Posted January 10, 2005 Share Posted January 10, 2005 i thought the most universal op amp was the 740? Link to comment Share on other sites More sharing options...
5614 Posted January 10, 2005 Share Posted January 10, 2005 i thought the most universal op amp was the 740? i thought the most universal op amp was the 741? well it is where i use em! and looking at electronics computer software which program circuits and compile PCBs the 741 is always listed as an option, the 740 is never mentioned, of course with the PCBs all you need is any 8 holed pin, but still, it calls it a 741. Link to comment Share on other sites More sharing options...
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