USB to TTL Serial Converters

Projects Networking, Protocols, and Devices
1

Hi all,

I have a project that takes it's input from a PC program. The output from the PC program is in the form of the combination of HIGH/LOW states of the RS232 DTR and RTS pins (ie HIGH/HIGH, LOW/HIGH, HIGH/LOW, LOW/LOW).

So far I have used a USB to RS232 cable, and a MAX232 IC to convert the signals to TTL and then input the signals to a couple of Arduino pins.

What I am wondering is if the devices like the one in the link below can help me make this level conversion easier?

What am I not sure of is whether this device can be used to get DTR and RTS output or whether it is only meant for input to the PC.

Any advice warmly appreciated.

Joe

2

Those are indeed the DTR and RTS from the computer that you need.
Do you have a logic analyzer, you should be able to see the data at those pins.
I think the CP2102 is a 3.3V chip. A 5V Arduino board might have trouble reading those signals.

There are many modules for usb-to-ttl-serial modules. You don't need to scale up to RS-232.
They often use one of these chips: CP2102, PL2303, CH340G, FT232R.
The FT232R (FTDI chip) is dangerous, because there are many counterfeits FTDI chips, and the FTDI driver tries to give you a bad day if you have a counterfeit chip. So don't buy this one, even if that is an original FTDI : SparkFun USB to Serial Breakout - FT232RL - BOB-12731 - SparkFun Electronics

3

Buy your FTDI chips from a reputable source and you won't have a problem.
3 that I use all the time:
www.tinyosshop.com for FTDI Basic type modules with microUSB and miniUSB connector
www.mouser.com for MIKROE483 FTDI module great for mounting on a board
www.digikey.com for FT232 chips when I want to put a chip on a board.

Ebay and Amazon are not reputable sources.

4

I would avoid the prolific ones also. I received a fake when I spent extra money to get one from what I thought was a reputable US seller.

It's nice to buy a complete package instead of loose chips from mouser or digikey.

If I get annoyed with my fake prolific adapter, I'm going to buy a CH340G. Those are cheap enough I don't think anyone is putting out fakes.

The problem is with the fakes (ethics aside) isn't with the chip, it's that the original companies make the fakes fail to function with the drivers.

5

Here is one that will do the job. It has all UART signals on one row and some GPIO along the other. It outputs TTL and has a jumper on the end to select 3v3 or 5v operation. I use one between a Mega2560 and a laptop running a program written in Lazarus with a link speed of 2Mbps. All of the handshake lines work as I use them with jumpers to identify the board and port amongst others connected via USB. TMK, the chip is a geniune FTDI.

6

Thanks for the replies, guys, very helpful and I'm very interested in the devices Eddie and CrossRoads have mentioned. I've ordered them to test them out.

On the same subject (kind of), I'm looking for an app or batch file (or something) that will let me toggle the DTR and RTS outputs LOW/HIGH, this would save me a ton of time in testing the project out. Does anyone have any ideas on this?

Thanks again for your advice, things are progressing really well.

Joe

7

Use one of the terminal programs RealTerm or HTerm as they both have handshake signal control.

8

Great advice, Eddie, thankyou!

http://realterm.sourceforge.net/index.html#Pins__Status

Looks like Realterm will save me a load of time!

9

USB to TTL Serial Converters

You might be able to use boards like below that use the CH340G chip, and tap off of the chip the desired serial lines. The bottom uno board appears to have four solder rings adjacent to the apparent CH340G chip that might be of use. You might need to look at the CH340G data sheet to see the chip pinouts.

http://www.ebay.com/itm/USB2-0-To-TTL-6Pin-Converter-Arduino-CH340G-for-STC-PRO-Serial-Replace-PL2303-/321754572767?hash=item4aea1127df:g:12MAAOSwymxVPddi

10

Be sure the adapter has all the UART signals available. Most only include DTR for the CPU reset function.