tux Posted August 19, 2003 Report Share Posted August 19, 2003 alright i talked briefly w/ shelby about this for a friend and actually i had a better idea and wanna use it myself but only have it "cooler" so we both want this circuit here's what i wanna do supply voltage is 12v (auto) i gotta drop voltage down to 5v for motorola absolute manifold pressure sensor sensor appears to output -4.9 to +4.9 depending on boost reading. now whats gotta happen is trigger a 12v lamp (for me .24amp) and LED for him so according to what i'm thinking i gotta use resistors to drop resistance down from 12v to 5v then go to map then from map increase the output to something between 0-12v (at least i think so the lamp/led would increase in brightness) or maybe i'm wrong and need it increase to +12v and ramp the amperage? but anyways i think it'd be voltage so ramp up to 12v and it appears to go from +/-4.9v i need to use an op amp to hop it up to 0.xx volt to +12 volt anyone have any idea how this circuit is done? thanks andy Link to comment Share on other sites More sharing options...
_Jason Posted August 24, 2003 Report Share Posted August 24, 2003 i'm sure there is a much better way.... to drop the voltage from 12 volts to 5 volts, i'd try and find a cigarette lighter voltage converter like the ones that come with portable cd players. they're fairly cheap and abundant, plus they take a lot of the guesswork and calculations out of it. =) the problem with using a resistor would be the wattage. using V: 12 - 5 = 7v I: .24 amps R = V / I = 50 ohms P = V * I = 2.88 watts, which would require a fairly large resistor, or a network of several resistors. as far as driving a lamp off of the output of the chip, check and make sure it can source that much current. many cmos chips can't, you could hook the output to a transistor to try and achieve the light getting brighter as the voltage increases. unfortunately i don't remember how to find out the type of transistor you need based on the ohmic region... i just remember it involved math. =( if you want the light lit at 0 volts, you'll need to amplify the source somehow. but you already knew that, so sorry i'm not much help. Link to comment Share on other sites More sharing options...
starquestPilot Posted August 24, 2003 Report Share Posted August 24, 2003 Your're going to have to be more specific... Which Motorola sensor are you intending to use? I need the part number. If the sensor needs -5 to + 5 volts, where is the -5v coming from? At what pressure (vacuum) is the indicator supposed to light? In other words, what is this circuit intended to tell you? I can build it, but I need more information... Thanks, Mike Link to comment Share on other sites More sharing options...
89onaquest Posted August 25, 2003 Report Share Posted August 25, 2003 look up the Lm3914 you can feed Power the chip 12-24V with no regulator. If you go series, you can get .5V increments on an LED readout drive. Link to comment Share on other sites More sharing options...
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