Saturday, November 30, 2013

USB Serial Converters, You don't need to buy one for each device.

I've been meaning to write about how to avoid having to buy a USB serial converter for every single radio, wireless router, microcontroller, or home automatic project.  Particularly because of all of the issues with counterfeit Prolific chips and driver woes. FTDI is the most desirable USB serial converter chip to have, but the premium is $10-20 at least for each cable.

You can use one USB to serial converter cable and adapt it to multiple devices, but you need to match voltages.  Devices can either be
  • RS-232 (-12Vdc to +12Vdc, or more commonly -5Vdc to +5Vdc).  This is the good old-fashioned serial that has all but disappeared from modern electronics.
  • TTL (0 - 5Vdc)
  • LVTTL (0 - 3.3Vdc)
[I Still Need to Add a Lot More Here]

The Chinese radio manufacturers (or maybe I should say accessory manufacturers have come up with an answer which could be a blessing or a curse.  They are now selling 6-in-1 or 8-in-1 radio programming cable kits which include one USB serial adapter which brings out 3 wires (RX, TX, Gnd)  in a 3.5mm TRS phone plug/jack set.  There are a set of cables to adapt to a number of different radio styles.

The Good news -- These are available for around $10 and should be useful to peuple who own multiple radios or need to program other people's radios, like clubs and emcomm groups.

The Bad news:
  • The converter is based on, you guessed it, the same crap counterfeit Prolific chips that fill every group I read with the same driver related questions over and over.
  • Because it's plug and pray, it will be easy to experiment and possibly/probably damage some electronics. 
Fortunately, it should be pretty easy to replace the USB serial converter component with one that is based on the FTDI or CP2102 (or CP2103).  I should probably write up a project.  Bonus points would be:
  • Adding TX/RX LEDs to assist with diagnosis
  • Adding over-voltage protection
  • Detecting and protecting against reversed connections
  • Ability to get at RTS/CTS lines for other uses.

No comments: