HellasTechn
- Apr 14, 2013
- 1,579
- Joined
- Apr 14, 2013
- Messages
- 1,579
Dear friends,
About 3 years ago i came up with the idea of creating a circuit that would be used as a safety feature in a computer that requires GPS at all times (the reason for that is not important now).
At that time Chris provided me with a very simple but yet very reliable LM555 circuit that monitors No1 GPS output and in case of signal absence it would flip the computers input to No2 GPS output through a relay array.
https://www.electronicspoint.com/threads/help-with-data-switch.259040/
the protocols involved here are RS-232 or RS-422 at baud rate 4.800.
I noticed that the receivers on their internal screen indicate an error estimation and it was then that i started thinking how to upgrade the above circuit in order to make it monitor not only the signal presence but also siglan quality.
I know that the GPS receivers use NMEA sentences. Each NMEA sentence provides different information. So the error estimation must have something to do with the receiver utilising some NMEA sentence to calculate error [DOP (dilution of precision)].
After googling for NMEA sentence error calculation i came up with this :
http://www.gpsinformation.org/dale/nmea.htm
GSA - GPS DOP and active satellites. This sentence provides details on the nature of the fix. It includes the numbers of the satellites being used in the current solution and the DOP. DOP (dilution of precision) is an indication of the effect of satellite geometry on the accuracy of the fix. It is a unitless number where smaller is better. For 3D fixes using 4 satellites a 1.0 would be considered to be a perfect number, however for overdetermined solutions it is possible to see numbers below 1.0.
Finally i am thinking if it would be possible to replace the 555 circuit with an other one powered by a Picaxe microcontroller and a program that would read nmea data from the inputs and determine which is better to bo fed to the output.
I am completly ignorant as far as programming is concerned but i am willing to study (at least picaxe).
Do you think it may be possible to complete this project ?
I am really open to suggestions.
Thank you.
About 3 years ago i came up with the idea of creating a circuit that would be used as a safety feature in a computer that requires GPS at all times (the reason for that is not important now).
At that time Chris provided me with a very simple but yet very reliable LM555 circuit that monitors No1 GPS output and in case of signal absence it would flip the computers input to No2 GPS output through a relay array.
https://www.electronicspoint.com/threads/help-with-data-switch.259040/
the protocols involved here are RS-232 or RS-422 at baud rate 4.800.
I noticed that the receivers on their internal screen indicate an error estimation and it was then that i started thinking how to upgrade the above circuit in order to make it monitor not only the signal presence but also siglan quality.
I know that the GPS receivers use NMEA sentences. Each NMEA sentence provides different information. So the error estimation must have something to do with the receiver utilising some NMEA sentence to calculate error [DOP (dilution of precision)].
After googling for NMEA sentence error calculation i came up with this :
http://www.gpsinformation.org/dale/nmea.htm
GSA - GPS DOP and active satellites. This sentence provides details on the nature of the fix. It includes the numbers of the satellites being used in the current solution and the DOP. DOP (dilution of precision) is an indication of the effect of satellite geometry on the accuracy of the fix. It is a unitless number where smaller is better. For 3D fixes using 4 satellites a 1.0 would be considered to be a perfect number, however for overdetermined solutions it is possible to see numbers below 1.0.
Finally i am thinking if it would be possible to replace the 555 circuit with an other one powered by a Picaxe microcontroller and a program that would read nmea data from the inputs and determine which is better to bo fed to the output.
I am completly ignorant as far as programming is concerned but i am willing to study (at least picaxe).
Do you think it may be possible to complete this project ?
I am really open to suggestions.
Thank you.
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