Long time no hear! This was because I had nothing new to report. I did nothing new with Open USB FXO and I did not have the slightest idea why my prototype failed to work.
I still do not have the slightest idea. However, in a private conversation with one of the blog readers, I was convinced that letting people take a look at my work could help in spotting the error in my design, whatever this error is (this statement makes the funny assumption that the number of errors my design accounts to just one).
Therefore, I created a google code project for Open USB FXO. It can be found at http://openusbfxo.googlecode.com/, and the sources can be browsed at https://code.google.com/p/openusbfxo/source/browse.
Please do not take the correctness of any of the uploaded files (schematics, boards and libraries) for granted. They are uploaded just for public scrutiny and review, in the hope that someone else can spot this error that I cannot see myself. Hopefully someone will.
Open USB FXO 
February 23, 2013 at 7:37 pm |
What kind of problems is happening?
February 24, 2013 at 7:52 am |
Hi Ricardo,
Please check my previous blog post https://openusbfxo.wordpress.com/2011/09/13/stillno-satisfaction/ for a description of the problems.
Cheers,
Angelos
February 26, 2013 at 1:16 am
Hi Angelos,
I saw your circuits. Some advance in change BAV99 to MAX8888?
Regards,
Ricardo Landim
February 28, 2013 at 4:19 am |
Hi Ricardo,
Yes, MAX88888 is regulated and will deliver a stable voltage. In contrast, the diodes in BAV99 have a voltage drop that depends on the current drawn by the circuit and the temperature. It should deliver a volage close to 3.5V, but this is not guaranteed.
Angelos
March 5, 2013 at 2:17 pm |
Maybe you can use some developer kit of PIC. This will ensure that circuit is working fine and you will able to test some code.
March 11, 2013 at 1:17 am |
Hi Ricardo,
I am afraid that the problem here is not in the code.
Angelos
April 5, 2013 at 3:18 am |
What about this project ?
http://www.rowetel.com/blog/?p=1776
April 10, 2013 at 4:23 am |
Hi Aranga,
I have been inspired by David’s $10 ATA in the first place, when I started my Open USB FXS project (we are in Open USB FXO here). David’s line of thought, if I am not mistaken, is that one can get rid of the specialized-and-expensive telephony driver chips and do all the work in the microcontroller. I am not sure whether he has finished this project, but it is a very interesting project to watch.
I have followed a more conventional approach: try to provide a USB-based interface using the same telephony driver chipsets as the modules of David’s IP04 and IP08 designs do. I have managed to get FXS working, and I have sort of got stuck with the FXO case.
Cheers,
Angelos
April 6, 2013 at 5:46 pm |
Where did you buy Silicon Lab IC’s? What vendor sites?
April 10, 2013 at 4:25 am |
Hi Marcello,
I have been using mostly Mouser. They tend to have a stock of Silicon Labs chips.
Cheers,
Angelos
May 20, 2013 at 7:35 pm |
Hi Angelos,
This is a great great stuff, I was looking at your Job and checking your schematics. In your previous post you said that the PIC18LF2550 never start.
In the past I played with the 2550 in CDC mode and found that the most of the issues are the capacitors in the XTAL, VUSB and the power supply. In VUSB I recommend to use a 470nF ceramic capacitor. You already are using 22pF in the XTAL so that’s ok.
About the program, do you have basic routine to blink some LEDs? just to notice that the PIC’s program is up & running. Your change to the LDO chip must help a lot.
Please continue with your great effort, If I can help you with something please let me know.
July 3, 2013 at 11:22 am |
Hi navaismo,
It took me months to notice there was a comment from you. I apologize deeply. I have seen the same issues as you have with the 2550 in various prototypes of my FXS board. Halas, I have not managed to make the FXO board show even the slightest sign of life.
Cheers,
Angelos
May 31, 2013 at 8:59 am |
Have you been able to attack the problem recently, perhaps using a different programmer?
July 3, 2013 at 11:25 am |
Hi David,
I apologize deeply for taking ages to reply. No, I have not had any progress. It is not the fault of the programmer, this I can tell, because eventually the programmer worked and I had it compare the flash-stored program to that on the local computer file. It is either some weirdness of the PCB (because I had not managed to make the programmer “see” the PIC on *this* PCB) or some other error. Never had the time to look extensively into it though.
Cheers,
Angelos