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#1
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Question for Electronics Wizards.
Can someone tell me how to "pull down " a 6 volt signal to 3 volts?
Resistor? Where? How? P.S. Please don't tell me to cut the wire in half, I know that much.
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2007 C 230 Sport. |
#2
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The quick easy answer is Radio Shack.
Go there and buy an assortment of resistors, pretty much any of the standard resistor assortment packages they have are fine since you are talking low amps, low voltage. Grab your DMM (digital multimeter) and 4 d cell batteries. Electrical tape the 4 batteries together flashlight style and tape a red wire to the positive end and a black to the negitive end of your battery stack. You now have 6 volts. Try different resistors attached to the red wire and the resistor to the DMM red lead and the black wire to the DMM black lead. One or two of the resistors will get you very close to 3 volts. that is the elementary method for you. The expert way is to read the color bands on the resistors and find the one that completes the formula to reduce 6 to 3 volts. The way I would do it is turn my bench power supply to 6 volts and get my Fluke DMM and try a few of the assorted resistors I have until one gets me from 6 to 3 volts. More than one resistor can be used in line. I would try a resistor in the range between 100 ohm and 800 ohm is I remember correctly. The DMM will tell you right way if it is even close. Good luck
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Christopher Henkel 1990 190E 2.6 - Arctic white SOLD 1986 190E-16v - Blauswartze 1993 300CE - SOLD 2003 W208 CLK 320 Cabriolet - Magma Red |
#3
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@ crhenkel
Thank you, I will do it the way you described.
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2007 C 230 Sport. |
#4
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I don't really see how this question can be best answered with the limited info given. There is the obvious question of how much current will you draw at 3V? If you have more details there may be a better answer. However, you seem happy with the answer given.
__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine) 1988 F150 144,000 miles (leaks all the colors of the rainbow) Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra |
#5
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That would not work because you have no current. The voltage drop on the resistor depends on the load. What are you trying to do?
Mike |
#6
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It will work if the load is very low. But without the details it is impossible to make a good recommendation.
__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine) 1988 F150 144,000 miles (leaks all the colors of the rainbow) Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra |
#7
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I mean the measurement method crhenkel suggested would not work. Assuming meter has infinite resistance there would be no current in the circuit and the meter would still show full power supply voltage.
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#8
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What sort of signal are you modifying, on/off? If so you can use an LM317T voltage regulator and a few external parts. Cost about $3 at Radio Shack.
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#9
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Thanks for all the input.
I currently have a signal ( generated by an alternator ), that is 6 volts, going to a tachometer. I'm trying to " chop " it down to 3 volts.
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2007 C 230 Sport. |
#10
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You might have better luck modifiying the alternator. The signal won't be plain old 6V. It's got to be a wave form, so a simple resistor or voltage regulator isn't going to work.
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#11
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Yes, you are right. I thought he was describing a divider, but actually it is hard for me to understand what was being described.
__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine) 1988 F150 144,000 miles (leaks all the colors of the rainbow) Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra |
#12
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Usually "signal" implies some information is on it, such as a waveform, as was just mentioned. But since you say it comes from the alternator maybe it is just the power supply? It makes a big difference! Do you have a tach that needs a 3V power supply? That seems kind of odd. Is it usually battery powered?
__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine) 1988 F150 144,000 miles (leaks all the colors of the rainbow) Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra |
#13
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Try a pair of back-to-back zener diodes, fed by a resistor.
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#14
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This is as bad as an oil thread...
__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine) 1988 F150 144,000 miles (leaks all the colors of the rainbow) Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra |
#15
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Assuming that you don't need much current for a signal, put the 6 volts through a 10K resistor, and then connect a 2.8-3.0 volt Zener diode from that to ground. A 1N4148 diode in series with the 10K resistor would not be a bad idea in case of a failure (don't want anything feeding back to the 6 volts).
It might not be a good idea to use a 317 regulator for this because its response time might not be that good and it's "instantaneous" regulation isn't very good without capacitors-which will smear and distort the signal that you want. This assumes that the needed signal is "digital" - that is, a number of pulses per second, and not analog. My understanding of an electronic tach is that it is effectively digital.
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86 560SL With homebrew first gear start! 85 380SL Daily Driver Project http://juliepalooza.8m.com/sl/mercedes.htm |
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