Old is Gold

Greetings Experts,

I got an old beagle, rev B5. I want to connect its serial port. The problem is I have only USB. But I do have a USB to TTL converter (5v and 3.3v).

Can i connect this BB to the converter directly ? I think BB`s signal levels are +5 to -5. But i think RS232 standards are +12 to -12. So I dont think i can plug it directly to 5v converter.

Will it work If I use MAX232 based converted circuit ? I mean like this :

Computer`s USB port ------->USB to TTL converter( 0 to 5v, FT232 based)------------> MAX232 based converter---------------> BeagleBoard

Specifically, what I meant to ask is, what would be voltage at the output of MAX232 ? Will it be standard +12 to -12 or will it be +5 to -5 ? If its former, what do I do???

Thanks in advance,

Aurabindo J

3V or 5V TTL is not compatible with a serial port. You are correct that Tte MAX232 uses positive and negative voltages for the signaling.

You need to take a look at the System Reference Manual and buy the suggested cable and plug it into a USB to serial adapter…

Gerald

Thanks for the reply Gerald, but I dont have a serial port. So no use if i buy the serial port and connectors. There must be some way out. I`m planning to do this circuit to make it work with my 5v TTL converter:

path1102.png

I have modified the circuit from this page: http://sodoityourself.com/max232-serial-level-converter/ .
The difference is that pins 16 and 2 are shorted rather than connected through a capacitor. If there is capacitor, then an 8.8v (for Vcc = 5v) will appear at pin2. As a result, the voltage at pin14 is around -8.8v. If it is shorted, I find a negative voltage around -5v.

Looks like this would do, I`m just afraid to hook it up. Suggestions are welcome.

Best Regards,
Aurabindo J

What you have drawn here is basically the same as what i a lready on the board. What is on the TTL side of this schematic? Where does it connect to?

If you look at the MAX232 datasheet, it will except up to +/- 30V. So 8V is ine on the receiver.

Gerald

path1102.png

What you have drawn here is basically the same as what i a lready on the board.

Yeah, Just removed a capacitor. Just drawn it to get familiar with Kicad. Just started using it :smiley:

What is on the TTL side of this schematic? Where does it connect to?

It is a USB to TTL converter, which connects my computer to MAX232 : http://www.rhydolabz.com/index.php?main_page=product_info&products_id=304 like Computer`s USB port <----------> TTL converter <----------> MAX232 <------> beagle