Serial to USB cable - varying results

[Charles Linquis]

As long as you are not attempting to bootload, then I think you will have no trouble. I have at least 4 brands of serial-USB adaptors, and all work fine. After you install, you may have to open up Windows Device Manager and go into the driver/properties tab in order to change the com port assigned to the device. I had one that installed itself as Com 12!

[brid0030]

Hey Charles. Thanks, but I don't think it is that simple. I have a 'no name' serial to USB cable that works with other devices, but not with the PIC/MAX232 setup. One of my collaborators reported that there was no readable communication using a radio shack cable and a compaq presario, but she got it to work with the same cable and a newer vista computer. So I don't think all cables and computers are created equal when it comes to serial to usb. I'll post what I learn when I get cables in the mail.

[Charles Linquis]

Maybe you found a bad one. I made a loopback tester that just connects pins 2 & 3. I plug it in, and press a key. If I see an echo, I have the right COM port selected, and it is working.

One thing: I never use any form of hardware handshaking.

[keithdoxey]

Another thing to bear in mind is that if you plug the USB Serial Adapter into a different USB Port (either on the PC or a hub) it will get "reinstalled" as a completely different serial port hence the high com Port numbers some people get upto.

You also cant uninstall a USB Serial port if it isnt physcially connected but you can steal the Com Port number that it was occupying in Device Mangler

[Mike, K8LH]

I do it a bit differently and so I am able to connect even the lowliest 8-pin 12F683 project to USB for a modest $2.68 investment (plus the cost of connectors).

I use a 'clone' Nokia CA-42 cell phone cable (USB to TTL level serial) available from one of several different Chinese vendors on eBay which uses the Prolific PL-2303 IC instead of an FTDI IC. Here's one of the vendors I use; Nokia CA-42 + CD, $2.68



I cut off the connector on the cell phone end of the cable and replace it with a 3.5mm "stereo" plug. I wire up the WHT (phone Tx), GRN (phone Rx), and BLK (ground) wires. I put a matching 3.5mm "stereo" jack on my PIC project boards and I'm in business (no MAX232 or equivalent level shifter IC required). Please note that there is no 5v wire in the cable (bummer!).

I've been using a 3.5mm "serial port" jack on my project boards for years (to save space) along with a simple two transistor RS232-to-serial adapter cable. Now I have the luxury of using those project boards with the RS232-to-serial adapter cable or the new USB-to-serial adapter cable.



The image above is of a successful serial bootloader download using my CA-42 USB-to-Serial cable.

Regards, Mike, K8LH

[keithdoxey]

Great tip Mike.

Looked a bargain at $2-68 then I discovered it INCLUDED shipping !!!!

Got 2 on the way to me now

[rmteo]

I cut off the connector on the cell phone end of the cable and replace it with a 3.5mm "stereo" plug. I wire up the WHT (phone Tx), GRN (phone Rx), and BLK (ground) wires. I put a matching 3.5mm "stereo" jack on my PIC project boards and I'm in business (no MAX232 or equivalent level shifter IC required). Please note that there is no 5v wire in the cable (bummer!).

Regards, Mike, K8LH

Do you know if perhaps other signals are available on this cable - in particular RTS and CTS? Thanks.

[Mike, K8LH]

Well, it's kind of a "good news" and "bad news" situation, I'm afraid...

The PL-2303 circuit board on the "business end" of the cable includes pads for 3.3v (<50ma), 5v (<100ma), RTS, CTS, etc. but since the cable is molded you have to cut away the blue plastic molding and the black rubber potting underneath to access to the circuit board. Here's what you end up with;



It seems that each new generation of clone cables are cheaper then the last. If you check out the original Jonathan Thomson article that caught my attention you'll find that earlier versions of the cable had a removable shell at the USB end and had more wires to work with and so that's kind of a bummer(!).

Regards, Mike