which USB to serial converter?

[MikeGyver]

So I was programming a picaxe and somehow in the process something on my workbench arced to my serial cable and now my serial port on my laptop is dead. As I recall it arced to the tip of the headphone jack end of the cable (ground).

Anyway instead of buying a new motherboard for $100 I want to get a good USB to serial converter. I also need my serial port for tuning my car, so simply buying the picaxe USB cable isn't a good option.

I've heard most converters suck. So what ones are good and work for most things? what should I look for/stay away from?

 

[boriz]

Look for:
High voltages floating around on workbench.

Stay away from:
High voltages floating around on workbench.

(Sorry, I couldn’t resist)

I like my serial port. USB is the ‘dark side’.

 

[inglewoodpete]

Maybe I was lucky a couple of years ago. When my serial cable was plugged into the sound port of my PC, the soundcard was the loser. (I have children: I bred, I pay the price hey Boriz?)

The recommended cables are the AXE027 (USB to stereo mini plug) or USB010 (USB to DE9 (DB9)).

The most important thing is that the cable uses the Prolific USB to Serial protocol chipset. Two of my friends use USB to DE9 plug cables purchased from Jaycar in Australia. These cables use the Prolific chipset. If you choose a 3rd party supplier, you must use the drivers supplied by Revolution Education. I found out the hard way that drivers from the Prolific website do not work with PICAXE on my PC.

 

[hippy]

The AXE027 USB-to-Serial cable uses the FTDI chipset. The same as used by other manufacturers who have serial downloadable product and I've personally not had any problems with FTDI drivers on Win 98SE nor WinXP.

 

[Mycroft2152]

M,

The reason most USB converters "suck" is that the PICAXE chip requires a non standard output, the Rx and TX signals have to be inverted. This is done from within the drivers.

If you have a FTDI chipset you can download a free programmer to reset the signal to be PICAXE friendly.

This has been covered previously, run a forum search on FTDI USB.

Myc

 

[westaust55]

AXE027 Serial Cable

I also have been using the AXE027 USB to Serial cable (thats the one with the stereo plug on PICAXE end) without any programming problems at all using WIN XP.

Only thing to watch, is that if you start up the Programming Editor without the AXE027 cable connected to the PC (not a problem if the PICAXE end is not conencted at this time), then the PE software cannot find the AXE027 and defaults to COMM port 1. What you have to do then is to manually select from the PE toolbar:

View / Options / Serial Port ​

and then set the comms port to the correct port for the AXE027 cable.

 

[BeanieBots]

I have both the AXE027 and USB010.
Like westaust55, no issues with the AXE027.
The USB010 however, won't program an 18X. Fine with everything else and all other PICAXE chips.

 

[hippy]

The reason most USB converters "suck" is that the PICAXE chip requires a non standard output, the Rx and TX signals have to be inverted. This is done from within the drivers.

Most USB-to-Serial converters should put out an idle low ( 0V or -Ve ) / active high ( +Ve ) signal as comes out of a physical serial port. This is the way all Rev-Ed USB-to-serial cables are configured when shipped.

This is compatible with the PICAXE download interface and should be compatible with all devices with a 9-way D serial connector providing the USB-to-serial output voltages are compatible with what that device requires.

Only when a USB-to-serial cable is connected directly to the High Speed Serial connections of a PICAXE without using a MAX232 or similar inverter does the output of USB-to-serial need to be reconfigured to be inverted.

The AXE027 USB-to-serial products should be usable with other serial devices out of the box providing they expect idle low / active high signalling, are voltage compatible, and only need RX, TX and 0V connections. It will of course be necessary to build a 3.5mm Jack to 9-way D converter.

 

[BeanieBots]

Does the USB010 support full hardware handshaking or just Tx,Rx & 0v?

 

[hippy]

I've not used the USB010 but would expect it supports all signalling and hardware handshaking. From the USB010.PDF - "Supports the standard RS-232 Serial Interface", and the same on the Prolific website ...

http://www.prolific.com.tw/eng/Products.asp?ID=59

 

[BeanieBots]

Thanks, I was aware of the chip capabilities, it was more a question if the cable supported it. Time to play I guess.

 

[gengis]

The one I got from Anderson worked right out of the box. Only a foot long so needed an extension.


http://www.phanderson.com/picaxe/picaxe.html

 

[Technical]

The reason most USB converters "suck" is that the PICAXE chip requires a non standard output, the Rx and TX signals have to be inverted. This is done from within the drivers.

This is totally incorrect, the PICAXE requires a normal signal as you would find on any traditional 9 way serial port - otherwise none of our serial cables would have ever worked!

So if the 'universal' USB adapter ends with a 9 pin port, and has a prolific chipset (as most of them do), it will work with PICAXE. The USB010 is like this and supports all handshaking.

 

[evans_us]

Good USB to serial

I have had good success with the Keyspan products in XP and VISTA. They make single units as well as 4 port expanders. The ports can be selected in their software. I use 2x 4port units running a robotics setup and have never had problems. The single units have worked fine both on PCs as well as my laptop (sometimes issues in powering USB show sup here) so I highly recommend these. The single ended unit is ~$35 and the 4port is ~$120.
Here is the link to theiir website: http://www.keyspan.com/products/usa19hs/

Programming for picaxe works with single units

 

[Mycroft2152]

This is totally incorrect, the PICAXE requires a normal signal as you would find on any traditional 9 way serial port - otherwise none of our serial cables would have ever worked!

So if the 'universal' USB adapter ends with a 9 pin port, and has a prolific chipset (as most of them do), it will work with PICAXE. The USB010 is like this and supports all handshaking.

Technical,

Hippy's response was more responsible and informative.

Your response is true, but only if you apply a very narrow set of qualification.

Again, it all depends on your definition of "standard" and all the qualifications you want to add.

The point is that if someone buys a "standard" USB adapter, let's say from Sparkfun, it will not work with a PICAXE even though it will work with many other micro controllers. There have been many posts about problems with USB adapters and PICAXE both here and on other forums.

It is unfortunate because it should be a non issue and a not a stumblng block to use a PICAXE.

Myc

 

[hippy]

Again, it all depends on your definition of "standard" and all the qualifications you want to add.

The best "standard" is what polarity is carried on an RS232 cable, what comes out/in of the PC, what comes out/in of a 9-way on any RS232 device and what comes out/in of a USB-to-serial cable.

The standard there is Idle-Low / Active-High - That's what all the Rev-Ed USB cables use.

The point is that if someone buys a "standard" USB adapter, let's say from Sparkfun, it will not work with a PICAXE even though it will work with many other micro controllers.

That's a case of them not being "standard" USB adapters. If they are not Idle-Low / Active-High they will not work with millions of RS232 devices in the market without needing reconfiguration.

It is unfortunate because it should be a non issue and a not a stumblng block to use a PICAXE.

It is a non-issue for anyone buying a standard USB-to-serial cable whether from Rev-Ed, Maplins, Tesco, PC World, Walmart or wherever. It's when people buy USB modules from Sparkfun and others which are configured for direct connection to microcontrollers which do not use RS232 signalling standards that there's a problem.

Rev-Ed USB-to-serial cables are standard RS232 polarity. It is those modules which are not which cause problems Those modules will not interface with any serial device using 9-way D's / RS232 without being re-configured.


Bootnote

The world uses standard RS232 - Voltage may vary but polarity is Idle-Low / Active High.

Any standard USB-to-Serial cable will comply with standard RS232 - Again voltage may vary but polarity is Idle-Low / Active-High. If it were any other way the cables would not work with standard RS232 equipment.

The PICAXE download interface is RS232 polarity compatible. Thus it can be connected directly to a PC serial port or a standard USB-to-Serial cable. This ability is fairly rare for most microcontrollers and is one of the great and attractive features of the PICAXE. It allows a very simple and cheap interface to be used, just two resistors.

Other microcontrollers use an inverted signal because they expect a MAX232 interface to be installed between themselves and RS232. Having to add a MAX232 to every board using that microcontroller adds cost and makes it more difficult for end users to use ( where the PICAXE wins over them ).

With the advent of cheap USB modules which are voltage compatible with the microcontrollers, it was realised that the MAX232 could be done away with and the inversion done in the USB modules. That's why USB modules which connect directly to such microcontrollers have inverted polarity outputs compared to standard USB-to-serial cables. They work with the microcontroller they are designed for but are absolutely useless for connecting to standard RS232 devices unless re-configured for that purpose.

 

[Michael V]

Great Explanation

Great explanation Hippy.

Ive tried about 6-7 of these all bought from various people on Ebay.
It's true, the ones that have the Prolific chip set all work fine for the standard two resistor picaxe download circuit. They load up as a Com port, and when they install on Vista and XP they say Prolific chip set, com port no XXX ready for use, or words to that effect.

The ones that come up as a "Human Interface Device" - even though it says they are succesfully installed, they don't work. Must be some other chip set. The sellers usually don't tell you the chip set though.

If you are going to use a few of these - eg one for programming, one or two for reading serouts so you don't have to keep plugging, plus USB hubs you will find that your computer will add com ports till the cows come home (Sorry Stan, sheep) The picaxe programming editor only goes up to 16. You can change the name of your new com port, covered on the Picaxe Reved USB Cable data sheet.
Michael

 

[Mycroft2152]

Thanks Hippy,

That was a straight, informative answer -- finally.

Keep up the good work.

Myc

 

[hippy]

@ Myc : After a night's sleep I can also see more in your "standard" for USB modules as Sparkfun et al sell.

What it really boils down to is USB-to-Serial cable is not equivalent to USBA-to-USBB cable plus USB module, only equivalent after the USB module has had its outputs inverted.