#1 2015-04-13 14:11:21

desarrolloayv
Member
Registered: 2015-04-13
Posts: 5

Problems trying to get it all running

Hello everyone, i've been working on 2 modems and i am trying to make them work, but it doesn't seem to be right, well, here is the thing, i put it all together, and then i try to transmit using some serial transmitter software such as termite, when i transmit something i can see how the leds go on and off (send and receive from one modem to another, all cool til now) but when it comes to the data, i see no serial response from the modem receiving the data.

I am not sure of what is happening.

I would be really greatful to anyone willing to help me to get this up and running, i bet i can give back in some other time. I currently need this kind of urgent.

Thanks in advance.

Andrés

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#2 2015-04-13 16:09:16

Stanley
Member
From: Kuala Lumpur, Malaysia
Registered: 2014-12-01
Posts: 65
Website

Re: Problems trying to get it all running

A quick guess is that you are doing a back to back Rx-Tx 2 modem setup ( without using 2 handy )

If yr output level is mic ( only 50mV ) , the back to back receiving modem would NOT be able to decode anything as the analog0 is listening to 3.3V level ....

Try sending using Line Level ( 2.5V ) and see if the receiving modem is able to decode it...


Stanley
9W2SVT/ N5SVT
http://9W2SVT.blogspot.com

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#3 2015-04-21 16:43:25

desarrolloayv
Member
Registered: 2015-04-13
Posts: 5

Re: Problems trying to get it all running

Good morning Stanley, i got it up and running last week, i had some issues with some random bad connection since i redid it.

I have now a more simple question, is there a way in which i can change the bps in which the modem receives de data? i need that to build in a solution, and plus, is it possible to change the frecuencies so that the mark and the zero become "1420" and "2150".

I've been trying to modify these parameters, but they don't seem to work, not sure if i am changing them where i shouldn't or if i am missing any other change i must do.

I would really apreciate if you can help me with this.

Thanks in advance.

Andrés

Last edited by desarrolloayv (2015-04-21 16:51:11)

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#4 2015-04-21 22:12:42

markqvist
Administrator
Registered: 2014-12-01
Posts: 112

Re: Problems trying to get it all running

Hi Andrés!
Are you wanting to change the bitrate of the data coming from the serial port to the modem, or the actual bitrate of the modulation/demodulation? Also just out of curiosity, why do you want to change the frequencies to 1420 and 2150 Hz?

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#5 2015-04-22 00:01:22

desarrolloayv
Member
Registered: 2015-04-13
Posts: 5

Re: Problems trying to get it all running

Hi!! Mark, first of all, thanks a lot for this masterpiece, right now there is a developement of a modem made by the company i work for, they made an aproximation to the bell 202 but it is not just the same, and those were the parameters they made:

Frecuencies: 2150 and 1420, not sure so far why those values, but they've been up for quiet some time.
Bitrate: well, i've looked up the references of the modem that was made here and the input bitrate is at 1200 bps; so i guess is that what i need. It was developed with some XR chips for fsk mod/demod.

So how this should be is 1200 of bitrate from the serial port to the modem.

Thanks a lot for the quick answer, hope i am giving enough info for you to help me out.


Regards

Andrés.

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#6 2015-04-22 10:06:31

markqvist
Administrator
Registered: 2014-12-01
Posts: 112

Re: Problems trying to get it all running

Thanks a lot smile
I don't know what firmware and source code you are currently looking at, but I just did some quick tests according to your previous post, using the MicroAPRS firmware. It works fine with alternate frequencies and baud! smile Try this:

In device.h change

#define BAUD 9600

To:

#define BAUD 1200

And in AFSK.h change:

#define MARK_FREQ  1200
#define SPACE_FREQ 2200

To:

#define MARK_FREQ  1420
#define SPACE_FREQ 2150

That's really all you need to do. I  tested this sending some APRS packets back and forth using Xastir on linux. Here's a sound recording of the two different frequency selections. You can hear the difference, though it's not very large!

http://unsigned.io/wp-content/uploads/2 … tfreqs.wav

But obviously, all of this depends on whether your current modem implementation is using AX.25 and HDLC framing, which is what APRS, and therefore the MicroAPRS firmware is using. If your current solution is using some other protocols, these would need to be implemented in the MicroModem for it to be able to "understand" your company's current modems.

It's all very interesting! Would you mind telling more about what you are trying to accomplish, and what the current modems are used for?

Many kind regards,

Mark

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#7 2015-04-22 14:31:10

desarrolloayv
Member
Registered: 2015-04-13
Posts: 5

Re: Problems trying to get it all running

Hey Mark, you are very kind and helpful!! THANKS

Well, the company i work for uses afsk modems for remote data transmission (through radio) of wheather variables such as temperature, river levles, etc...

Currently the XR mod/demod modem developed by the company is running out, and is each time more expensive due to the components, so, the main idea of the solution i am trying to make based on your developement is the substitution of that modem. Right now i am using the BertOS version of your modem, basicly because i know very little about the APRS and i do not requiere such task to be done in my particular case. I'll try to implement it so that i can make those changes, and upload it to the 2 UNO's i've got.

Thanks agian Mark.

Hope i can be giving back in the forums!!

Andrés  big_smile big_smile big_smile !!!!

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#8 2015-04-22 15:29:04

markqvist
Administrator
Registered: 2014-12-01
Posts: 112

Re: Problems trying to get it all running

Very interesting! Sounds like an exciting job you have!
Well, I will really urge you to not use the old BertOS codebase. The new codebase I have made is totally free of any BertOS code, and it is much more lightweight, easier to understand and adapt, and much nicer on resource usage of the MCU. The problem is though, that currently I have only build APRS-specific firmwares with this codebase, and as you say this is not what you need. I would also say that using the AX.25 format and APRS style messaging would be a bad fit for your needs.

Just to let me understand correctly, you are looking to make a solution that will also be able to talk with the old modems, right?

Does any data and specifications on the frame format of the current modems exist? Maybe I could even help you guys write a firmware that will fit your needs. Creating a new "general purpose" firmware with the new codebase has been on my todo list for a while, but I have been so busy with other projects that I haven't done it yet.

I'd be happy to discuss it with you over a skype call if you want!

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#9 2015-04-22 17:08:02

desarrolloayv
Member
Registered: 2015-04-13
Posts: 5

Re: Problems trying to get it all running

HI Mark

Indeed it is a quiet interesting job! and yes, you are right, that is the main goal of the solution i am working on, to have them both wroking correctly.

I sent you an e-mail with my infos so that we can get in touch!!

Thanks!

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