voltage converter help please
 

ok so ive been thinking about my afm to map sensor thread and i have a idea but i have no idea about how to build something that would take a 0-12 volts input and convert it to a 0-5 output voltage any ideas or suggestions would be appreciated

It can be easily done with a few resistors and wiring a voltage divider circuit.
I'm sure you can find the right one by searching the topic. You are not the first person switching from a AFM to a map, so there should be a lot of good info on the internet.

i figured but i dont know what to call it somebody called it a translator anyway i found a calculator and i need to know at least one of the resistors values to do the calculator but i wouldnt even know where to start cause that would be alot of guess work for me

You can purchase a 0-12 Volt to 0-5 Volt converter at most Industrial Instrument supply houses. Some have adjustments to accurately adjust the output signal (0-5 Volts).

ok that sounds like the best idea but i cant find one anywhere could you help me please

Look in the telephone book and find an industrial instrumentation supply house. Rochester Instruments is one brand but they tend to be expensive so ask them if they have a source of low cost converters. Another source might be a large computer store or you will have to check online with someone like Tiger Direct. Best Buy might have them or could probably get one. You just have to search.

The voltage divider idea will work only if here is a constant load. If you know the load current you can calcualate the resistances and their wattage. You say there is a 0-12 supply and a 0-5 volt output. The ignition voltage when the alternator is running is more like 13.8 volts. It is not constant since it is at battery voltage when the engine is not running so more like 12.0 volts. Is the load always 5 volts? if so you can use a zener diode and a dropping resistor. There are zener diode calculators on the web. You will need to know the load current to size the zener diode and the resistor. I built one for my instrument cluster for less that $10 to replace the switching regulator in the fuel gauge.

BTW there is a solid stste device caled a voltage regulator that will take 12-14 volts and output 5 volts. I think it is a 7805 and it may e available at Radio Shack. If not it is available from Vetco or Mouser Electronic, NTE960 at Vetco for $3.73.

amateur wouldnt it output 5 volts all the time until the input coltage dropped below 5 volts?

Yes. It is a reguator so as long as the input voltage is high enough and it is not drawing more that its rated current it will hold the output voltage at 5 volts. If you are looking for an output voltage that is proportional to the input voltage then the voltage divider is the way to go.

BTW this thread reminded me that the electronic voltage reglator is a good way to go so I replaced the zener diode and rsistor in my instrument cluster with a 7809 voltage regulator which uses much less current than the zener diode method and stabilizes the fuel and temperature gauges veery nicely.

ok i think after i graduate out of my diesel tech class i need to go back for electronics because this is so far over my head im just so confused as to how to set up the voltage divider and everything

Ok now I think I understand what you are trying to do and in theory it could be done with a votage divider. The problem is that the characteristic of the MAP relative to goltage would have to be the same as the AFM. The AFM is not linear, however, and usually starts out with a relatively flat voltage drop followed by a steep voltage drop, followed by another relatively flat voltage drop. I don't know what the characteristice voltage of the MAP is but It doesn'r sound like it would follow the same voltages as the AFM. Here is a link to a typical AFM voltage characteristic. http://atlanticz.ca/zclub/techtips/afm/index.html.

I think I may have led you astray without understanding what you wer trying to do and for that I appologize.

no your good i thought i knew what i was talking about at the begining of the thread and after the first few replies i was lost
i knew that the afm wasn't exactly linear, i guess i just figured that the o2 sensors would compensate for the slight lean condition one end of the rpm and the rich condition at the other the only reason i really considered this was because somebady said they drove a pickup with no afm and it was really "woken up" by the lack of the most air restrictive box on the planet the Toyota decided to use on these motors