It Started With a Hardware Limitation I have been using Quectel GNSS modules in my designs for a while. They are reliable, well-documented, and the support ecosystem is solid. But the module I had been using had one problem that I kept running into: no external antenna support . For most projects that is a minor inconvenience. For a marine vessel monitoring and control system , it is a non-starter. A vessel hull blocks sky view, antenna placement is critical, and the difference between a clean fix and no fix at all often comes down to whether you can mount the antenna where it actually has line of sight. An integrated antenna in a sealed enclosure below deck simply does not cut it. So I went directly to Quectel. The Conversation With Quectel I reached out through their official sample request channel. I was not expecting much — most component manufacturers have a standard process: fill out a form, wait, get a few uni...
Today i completed the DTMF decoding circuit and interface it to the micro controller and DTMF tone was generated by the PC and fed to the decoder. After all the connections i wrote a test code for micro controller to get the decoded signal. With an interrupt i manage to get the decoded values from the tone generated. To view what i am getting i connected the LCD and found some problems and after a while i menage to fix it. from the flow you can see how it works. Then i have to test this from a mobile phone and for that i need to make a small preamplifier to control the volume.