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GPS Speed to voltage converter

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Squintz

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Ok this is a real life situation which i need to solve. I have a GPS receiver which puts out NMEA protocol all i need from the NMEA is the speed of which a vehicle is travling. But i need that converted to voltage so that i can feed it into a Data Aquisition System. I have not yet got my PIC programmer in the mail yet so i have not been able to learn how to use it. I this this is what i need to do.

The gps receiver can be programed to only ouput speed in the NMEA protocol. That part is easy. I need to program a PIC (This is where you guys come in) which will convert that NMEA output into a digital output and from there i can use a Digital to Analog Converter to supply the voltage to the System.

The system wil accept an input of 5v

its a 12 bit system so the 5 volts can span of 4095. we call the 4095 "Counts"

we read this as -2048 to +2048 and speed can only go positive so the span is 2048/5 = 409.6 Counts / Volt

how accurate can i get the Digital output to be?
Can anyone help me write the program?

The GPS receiver is powered by 12 volts!
 

crust

Member
If you are going to use a PIC, wouldnt it just be easier to have the PIC take the NMEA data from the GPSr on its own, skipping the D/A conversion? Beyond that, you would need to convert the decimal serial output of the GPSr into a binary value which you could then apply to a D/A conversion for input to the PIC. However, this has the added problem that you need to know the range and possibly how to scale the value before you apply it to the D/A, that is probably the hardest part -- in fact, it would be best to use a micro to do this.
 
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