I’m having trouble debugging the AVR-to-GSM modem serial communication.
Fortunately, my colleague has made me a circuit to view the communication. Unfortunately, it takes two serial ports just to debug the serial communication while my laptop doesn’t have any serial ports (I use USB-serial converter). So, I was thinking to buy another USB-serial converter, before I was struck by this idea.
Here’s the simplest circuit to debug the RS232 serial communication between two devices:
Believe it or not, although the signal that’s received by the sniffer is not 100% perfect, this circuit works !!
For diode, I use 1N4004 power diode (since that was the only thing that was inside my pocket). But if you want to make it better, I suggest to use Schottky diodes (since they have low forward voltage and fast recovery).
Anyway, there are other things that you should know too before using this circuit. First, you cannot use this circuit to debug full duplex communication (data is sent while other data is received at the same time). Second, the baud rate is limited by the choice of your diode (that’s why you need fast recovery diodes).
There’s other version of this circuit. Like this:
You can refer to the original site for the details of this circuit.