NMEA to RS232 Interface Board

  
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This design is based on that of Andrew Bruno. His design appeared under the name of `bruno-if`. My contribution was to provide Postscript files for a Printed Circuit Board. This circuit is quite old and goes back to the days of NMEA-0180 and 0182. Note that it is non-inverting. Its purpose was to shift the NEMA voltage levels to be RS232 compliant
NMEA to RS232 Interface Board - schematic

. Many early GPS units were not fully RS232 compliant, in the sense that they did not produce a negative voltage level. The voltages were at TTL levels, but in the same sense as RS232: Although not fully compliant, this meant that a GPS unit could be directly connected to many computer RS232 interfaces, but not to those that required the negative voltage. NMEA-0183 recommends that a talker output should have EIA-422 differential outputs and that the input circuit should use an opto-isolator with suitable protection circuitry. I cannot, therefore, recommend the use of this circuit with NMEA-0183 compliant equipment. ICs: MAX232CPE RS232/TTL Interface CD4049UBE Hex Inverting Buffer L7805C 5 Volt regulator Capacitors: C1, C2, C3, C4, C5 22 microfarad (electrolytic - 16 volt working) C6 10 microfarad (electrolytic - 16 volt working) C7 100 microfarad (electrolytic - 16 volt working for 12 volts in) (electrolytic - 50 volt working for 40 volts in) Resistors: R1, R2 4K7 ohm (4700 ohm) Diode: D1 1N4002 Power Diode Two Postscript files are provided. They can be printed directly or used as EPS files. When used as EPS files, they should not be subject to any further scaling.



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