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  #1  
Old 05-17-2021, 06:30 PM
RV8Squaz's Avatar
RV8Squaz RV8Squaz is offline
 
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Location: Senoia, Georgia
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Default RS 232 out signal

Is there a way to check for or confirm with a meter, an RS 232 out signal from a device such as a GNS 430? I know how to get into the configuration pages and change the settings. But how do I verify the signal is actually being transmitted? Itís going to an Artex 345, 406 MHz, ELT. Thanks!
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  #2  
Old 05-17-2021, 06:51 PM
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Ed_Wischmeyer Ed_Wischmeyer is offline
 
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Location: Savannah, GA
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Been there, done that, just last week...

The Artex can receive NMEA data at 4800 baud or some other format at 9600 baud. That baud rate is set at the factory and cannot be reset in the field without a specialized Artex programmer. In other words, just knowing that the GNS is putting out serial is not good enough, it has to be the right format. My guess is that 9600 baud is what you want.

Here's what I suggest: connect the GNS to the Artex, and that's easier to state than to explain. Turn on the GNS and let it establish a GPS position. Then hit the Test function on the Artex. If you get one long beep, all is good. If you get the five beeps of death, then the serial data is not being read properly. Try the other baud rate / format on the GNS and see if that gets rid of the five beeps.

You may get other beep groups if the Artex discovers other things that it doesn't like. The explanation of those beeps is in the Artex manual, available on line.

NOTE: There may be some gotchas of which I'm not aware, so please do not assume that I completely know what I'm talking about... Nor am I claiming that this advice is fully in compliance with all the regs...
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  #3  
Old 05-17-2021, 10:11 PM
rapid_ascent rapid_ascent is offline
 
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Using a DVM doesn't really work well for checking RS-232. As the data is transmitted the average voltage level changes. This tends to mean that you just see an average voltage value which isn't a good indicator.

For RS-232 it might be easiest to just buy a USB RS-232 adapter for your laptop. Then you can just see if you are getting data. This might come in handy for checking other RS-232 signals at some point.

There are also little breakout widgets which have leds that blink on transmission. A bare minimum test setup is just an LED and a series resistor which will blink on data transmission. These LED setups don't work well though for high data rates though.

I'd buy the USB adapter if it was me.

Remember you can monitor an RS-232 output by connecting an output to the input of your monitoring device (laptop) even if it is connected to the input of another device. However, don't connect 2 RS-232 outputs together. If you do this the two outputs end up fighting each other and it doesn't work at all.
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  #4  
Old 05-18-2021, 05:58 AM
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RV8Squaz RV8Squaz is offline
 
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Quote:
Originally Posted by Ed_Wischmeyer View Post
Been there, done that, just last week...

The Artex can receive NMEA data at 4800 baud or some other format at 9600 baud. That baud rate is set at the factory and cannot be reset in the field without a specialized Artex programmer. In other words, just knowing that the GNS is putting out serial is not good enough, it has to be the right format. My guess is that 9600 baud is what you want.

Here's what I suggest: connect the GNS to the Artex, and that's easier to state than to explain. Turn on the GNS and let it establish a GPS position. Then hit the Test function on the Artex. If you get one long beep, all is good. If you get the five beeps of death, then the serial data is not being read properly. Try the other baud rate / format on the GNS and see if that gets rid of the five beeps.

You may get other beep groups if the Artex discovers other things that it doesn't like. The explanation of those beeps is in the Artex manual, available on line.

NOTE: There may be some gotchas of which I'm not aware, so please do not assume that I completely know what I'm talking about... Nor am I claiming that this advice is fully in compliance with all the regs...
Hello Ed,

Thanks for your reply. I do have the manual, but I didnít get as far as the operational checks. Thanks for the summary. I am aware of the required settings/baud rate which is configurable on the 430. Hopefully I wonít get the five beeps of death.
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  #5  
Old 05-18-2021, 06:06 AM
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RV8Squaz RV8Squaz is offline
 
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Quote:
Originally Posted by rapid_ascent View Post
Using a DVM doesn't really work well for checking RS-232. As the data is transmitted the average voltage level changes. This tends to mean that you just see an average voltage value which isn't a good indicator.

For RS-232 it might be easiest to just buy a USB RS-232 adapter for your laptop. Then you can just see if you are getting data. This might come in handy for checking other RS-232 signals at some point.

There are also little breakout widgets which have leds that blink on transmission. A bare minimum test setup is just an LED and a series resistor which will blink on data transmission. These LED setups don't work well though for high data rates though.

I'd buy the USB adapter if it was me.

Remember you can monitor an RS-232 output by connecting an output to the input of your monitoring device (laptop) even if it is connected to the input of another device. However, don't connect 2 RS-232 outputs together. If you do this the two outputs end up fighting each other and it doesn't work at all.

Hello Ray,

Thank you very much for your response. I didnít know such a device existed. Great idea! Cheap enough and it would be a great tool to have for future use. Once connected to my laptop (an Apple Mac Air), what application would one use to monitor the signal?

Although, it sounds like a DVM may actually work for my purposes as I am simply looking for the presence of a signal.

Thanks for your help.
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  #6  
Old 05-18-2021, 07:12 AM
FinnFlyer FinnFlyer is offline
 
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Location: Bell, FL
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Default Cheap oscilloscope

Actually these days you can get really inexpensive oscilloscopes. Some simply plug into a USB port and uses the laptop as display. For RS-232 monitoring you do not need a high-frequency oscilloscope. 1MHz or lower would be plenty.

For some reason I'm having a hard time finding a one or two channel, really low-cost, low frequency USB oscilloscope or USB data acquisition module. Really shouldn't be more that $20-$30. Maybe you'll have better luck.

Something as simple as this would do fine to look at a RS-232 signal:
https://www.amazon.com/DSO138-Oscill...97794422&psc=1

and does not require a laptop. Just a 9V power supply.

Finn
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Last edited by FinnFlyer : 05-18-2021 at 07:32 AM.
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  #7  
Old 05-18-2021, 07:15 AM
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rv8ch rv8ch is offline
 
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Quote:
Originally Posted by RV8Squaz View Post
... Once connected to my laptop (an Apple Mac Air), what application would one use to monitor the signal?
This page has some hints.

https://pbxbook.com/other/mac-tty.html
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  #8  
Old 05-18-2021, 09:35 AM
rapid_ascent rapid_ascent is offline
 
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You can find free terminal application programs that will allow you to display the RS-232 data. You'll have to setup the BAUD rate and format to match the sending device.

RS-232 is really a hold over from the older days and was used terminals, old modems and etc., but its still a useful interface. It has a large signal swing so it tends to be somewhat immune to noise and etc.
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  #9  
Old 05-18-2021, 09:42 AM
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Draker Draker is offline
 
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Ray's advice is right: Connect the RS-232 output to a computer. Tx on the GNS to Rx on the serial adapter (pin 2), signal ground on the GNS to ground on the serial adapter (pin 5). Configure the software in the way you expect the GNS to output (baud, data, parity, stop bits), and verify data shows up in the software's terminal screen. If you are expecting NMEA, you'll see text sentences that kind of look like this:
$GPGSV,2,1,08,02,74,042,45,04,18,190,36,07,67,279, 42,12,29,323,36*77
$GPGSV,2,2,08,15,30,050,47,19,09,158,,26,12,281,40 ,27,38,173,41*7B
For software, I don't have much of a recommendation for Mac, but it's simple software--they all should work. Don't pay money for one.

Some "cheaper" USB to serial adapters can be (or at least used to be, in my day) flaky or simply not work. You should be fine with Belkin or some other big name. To test yours out before connecting to the GNS, wire pin 2 to pin 3, open up your software, and start typing. If you see what you type, it's working. When doing this professionally, I would always use ancient computers that have "real" serial RS-232 ports sticking out of them, rather than the adapters.

Good luck!
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  #10  
Old 05-18-2021, 09:45 AM
12vaitor 12vaitor is offline
 
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You can build a simple LED test light to see if your RS232 port is operating. The attached image is from the ACK ELT installation manual and should work with any RS232 port. I built the test light and an on/off switch into my panel next to the ACK ELT remote so I can periodically check the RS232 operation.

John Salak
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