USB to Serial Adapter - Page 1
Forum section: electronics / general

author: sony mavica
author_rank: Frequent Contributor
timestamp: November 11, 2015, 10:03:39 pm
content: how well do these work i have an old pda and a old camera both use Serial cableshow well do they would will be using on xp computer

author: retrolefty
author_rank: Super Contributor
timestamp: November 11, 2015, 10:09:12 pm
content: Quote from: sony mavica on November 11, 2015, 10:03:39 pmCan you be a little more specific? As a general note nearly every model arduino ever sold (but a few exceptions) uses a USB serial converter chip very successfully that work with MS, Linux, and apple OSs.

author: sleemanj
author_rank: Super Contributor
timestamp: November 11, 2015, 10:18:19 pm
content: Quote from: retroleftyThey use a USB-UART chip, that is a very, very different thing to a USB-RS232 chip that the original poster will be requiring.

author: sleemanj
author_rank: Super Contributor
timestamp: November 11, 2015, 10:22:20 pm
content: Quote from: sony mavica on November 11, 2015, 10:03:39 pmA device that plugs into a (near extinct) "serial port" is talking RS232 serialThe majority of cheap "USB to serial" converters (eg for connecting to microcontrollers) are plain old UART serialRS232 basically sits on top of UART, RS232 is inverted logic, uses negative voltage, and has a voltage span from like -12v (high) to +12v (low).UART is standard logic level, ie, 0 = low, Vcc=high.So in short, make sure you are buying an RS232 converter (most likely has a 9 or 23 pin serial port already on it), and not use a UART converter.

author: sony mavica
author_rank: Frequent Contributor
timestamp: November 11, 2015, 10:50:10 pm
content: Quote from: retrolefty on November 11, 2015, 10:09:12 pmthe pda is a Casio Pocket Viewer PV-100 will have to check the model of camera

author: Rick Law
author_rank: Super Contributor
timestamp: November 13, 2015, 03:15:27 am
content: Quote from: sony mavica on November 11, 2015, 10:03:39 pmUSB-serial converters work like a champ for me, but it also depends on if the Serial-USB converter you got supports the features you need.For example: With my UT61E dmm, the stock software only works with one of my converter (FTDI), whereas, with my home-grown software, I can use any of my three converters (FTDI/Polific/Philips chipsets) - difference is with my home-grown UT61E logger, I connect without turning on parity.One new thing you have to watch out for if you get a Serial USB converter with FTDI chipset. If the chipset is not a real FTDI but a work-alike/compatible/fake, the FTDI driver may disable the chip forever.

author: SpidersWeb
author_rank: Unknown
timestamp: November 13, 2015, 05:49:42 am
content: I also want to add that the USB interface doesn't have hardware interrupts, and those cheap adapters don't usually have a proper hardware UART chip in them.So for stuff like an Arduino or other devices that are a bit more dedicated to the port that only really need RX/TX anyway it's not a problem, but with devices that require handshaking these adapters often take too long to respond. With my testing I was finding each time the hardware handshaking was used I would lose between 1 and 3 bytes of data in the stream and this happened as low as 2400 baud - often a partial byte occured too which generates a whole bunch of junk. I was able to get around it in software by sending one byte, and having the software check the slave device was ready, then repeating but this cut performance by half - but long story short, if you need handshaking, just find a laptop / computer with a serial port still on it.I'm not an expert, just my personal experience.Considering how cheap they are though, it's almost always worth a punt.

author: TheSteve
author_rank: Unknown
timestamp: November 13, 2015, 06:40:15 am
content: I've always had success with proper FTDI based devices - everything else is a crap shoot. Often the others work fine, but you also have a good chance of having problems.Long story short - buy one that uses an FTDI chip and save yourself the potential hassles.btw, FTDI did "brick" the fake FTDI devices using one specific driver rev but they have long pulled that driver and stopped the bricking. You could also recover bricked devices with one of FTDI's own tools - you just needed to reset the VID and PID.

author: Galenbo
author_rank: Super Contributor
timestamp: November 13, 2015, 07:50:32 am
content: The problems I had with rs232 converters were all with really old gear, I think Y2K+ gear with a rs232 connector is told to be more tolerant.On 1 occasion we did some measurements, same device with a working/nonworking converter.The nonworking converter didn't have the voltage levels right, the difference was huge.So we assumed this was the only cause, and didn't look for other differences, timing, stability,...

author: sony mavica
author_rank: Frequent Contributor
timestamp: November 14, 2015, 11:04:41 am
content: thanks guys

author: Stonent
author_rank: Super Contributor
timestamp: November 14, 2015, 10:17:00 pm
content: I've seen some devices specifically say they will not work on usb to serial cables because of the tendencies of the usb to serial cables to use 5 volts output rather than 12. Also anything that uses bit banging won't work on usb to serial cables typically.

author: Galenbo
author_rank: Super Contributor
timestamp: November 15, 2015, 11:15:28 am
content: Quote from: Stonent on November 14, 2015, 10:17:00 pmCan you please document this? (i'm not trying to argue, just never saw this, and expected all Y2K devices got an update)The devices we had and didn't work, didn't mention it, because were released befor the existance of USB (converters)

author: ruffy91
author_rank: Regular Contributor
timestamp: November 15, 2015, 12:50:18 pm
content: Usually the problem with older gear and USB-RS232 isn't the converter bit the software that is not able to use VCP but relies on low-level control of the UART

author: joeqsmith
author_rank: Super Contributor
timestamp: November 15, 2015, 04:18:35 pm
content: I have ran into a few snags with them. One problem with Windows was that if the device was outputting data, Windows would see this as an old pointing device and start moving your pointer. FTDI has a function in the driver that will solve this.When NI released a new version of Labview, they screwed up the interface. Not sure how as Windows does everything for you and serial ports are not exactly a new technology. Non the less, they somehow managed it. Their advice was to buy their USB adapters. In the end, I tossed every USB adapter I had and switched to FTDI for everything.

author: Rick Law
author_rank: Super Contributor
timestamp: November 15, 2015, 10:15:32 pm
content: Quote from: joeqsmith on November 15, 2015, 04:18:35 pmI think it could be the USB/Serial PC's hardware ((in addition to / instead of) the rs232 device).I had this problem at times with my ancient machines but not with usb-rs232 devices. XP seem to get confused. My Sony V505 used to try to boot from the USB mouse thinking it is an HDD (or possibly external-CD). And with the Sony and another laptop (don't recall what the other one was), heavy USB-HDD activity will move the mouse cursor.

author: Stonent
author_rank: Super Contributor
timestamp: November 18, 2015, 04:19:50 am
content: Quote from: Galenbo on November 15, 2015, 11:15:28 amI know Velleman serial based PIC programmers don't work. The package even says so.

author: macboy
author_rank: Super Contributor
timestamp: November 18, 2015, 07:17:22 pm
content: Quote from: Stonent on November 18, 2015, 04:19:50 amThe main reason for this is that these programmers "steal" Vpp from the serial lines, which on a PC are driven by the +/- 12 V rails available inside. 12 V is just adequate for programming the PIC. But the USB devices usually use a charge-pump based voltage doubler to generate +/- 10V (more like 8 to 9 V) that is not adequate. Another potential issue is that they bit-bang the data and clock lines for the programming operation, but this would still likely work through USB, albeit at a limited rate. The voltage issue is a game-stopper.

author: Stonent
author_rank: Super Contributor
timestamp: November 19, 2015, 07:28:42 am
content: Quote from: macboy on November 18, 2015, 07:17:22 pmMy programmer requires external power.

author: Ian.M
author_rank: Super Contributor
timestamp: November 19, 2015, 07:36:23 am
content: Worse, Microchip's CDC driver isn't very good at keeping the control line changes synced with the data stream, and some s---tty USB <=> serial chipsets have a reputation for merging control line transitions. After all, as long as the lines reach the correct state a few ms later, who cares when they individually transition? You have to really slow down the bit-banging to get it to work, and it will fail if there's much else going on on the same host controller.