I want to use serial 3 to send to a second computer, so I can monitor variables on a second machine, while programming on machine one.
I have a USB to serial adapter, but read that rs232 is 12v. Are the USB to serial adapters actually rs232/12v, or can I simply hook from serial 3 TX on the Arduino to some pin on my usb/serial adapter?
It depends on your adapter - RS232 serial is indeed 12v (and even -12v!), and will quickly fry your poor Arduino. However, if you happen to have a TTL level serial adapter, it will probably run at +5v and 0v, as the Arduino expects. You can easily by TTL level usb-serial adapters from sites like SparkFun - the FTDI chip that older Arduinos have is a commonly used USB-serial IC, and breakout boards for it will cost you around $10-$15.
Alternatively, you can use a MAX232 IC to convert RS232 serial to TTL level serial, and use your existing adapter - it's just a bit more work, although probably cheaper if you get it right the first time.
This is just a device that has USB on one end and a 9pin serial mouse port on the other. How does it get 12v if USB is only 5v?
Do they contain DC to DC converters?
Seems like these would be safe, no?
some of them do contain capacitor based boost circuits. however if they are rs232 their output signal will be inverted and you will have to invert it again to get a signal that your arduino can understand. by inverting i mean a high on the converter needs to be a low to the arduino, and a low on the converter needs to be a high to the arduino.
I had one of these TTL adapters lying around so I hooked Arduino's TX to Pin 2 on the DB9. I can see it's sending data to the PC, but it's scrambled.
Any tips?
a ttl adapter or an rs232 adapter?
It's this USB to RS232 Converter: (an older revision)
I can see that the data is being sent, as the scrambled data gets sent at about the same speed as the data being sent to COM5 the normal way.
I have serial 2 of Arduino to pin 2 of the db9.
one of these
between the tx of the arduino and rx of the adapter.
There's info on the RS-232/ TTL issues at...
And more on serial / Arduino / PC issues at...
Are you saying just an inverter on the TX line like a 74hc14n?
So Arduino pin 1 tx out to 74hc14n pin 1 input
inverted IC output pin 2 to usb serial adaptor pin 2
5v to ic pin 14
0 v to ic pin 7
yeah
Very nice. That works.
Much appreciated.
glad it worked 