i like wireless, and i like the simplicity of the serial port. i have a bunch of devices (radio, gps, home vision, etc.) it would be nice to hook up, via bluetooth.
so, i finally broke down and bought a bluetooth rs-232 adapter to let me connect these serial devices wirelessly. simple right? while i was waiting for the price to drop on this --no luck there, still about $50-60. decided not to wait, and splurge on one.
turns out it's not quite a simple cable surrogate, as one might hope...
first of all, being a serial cable surrogate device, they do come in two flavors for the actual physical connector, DCE and DTE (data communications equipment, or data terminal equipment) --on the bluetooth side that's mirrored by the 'master' and 'slave' concepts.
DCE and DTE really just specify which wires transmit data/signaling --at each end. since i'm using my laptop (DTE) to connect to devices like a gps (DCE)... i got a DCE version. a switch on the device lets you swap the virtual master, and slave modes (on either version). the electronics are identical --so if you put a null modem in-line (which they ship with) you've got the other connector. all good.
in my case, the one item in particular i want wireless serial access --is my homevision controller. i'll admit, while i don't connect to it very often --i just want to make that convenient when i do, not to fuss with cables, or have to position the laptop (now tethered by wire) nearby!
another selling point motivating me, was that iogear makes an interesting version, you don't run external software like other vendors to configure the device (it uses external switches, and raw hyperterminal to access more advanced modes/settings). i already knew i'd have to plug in external power --still working on wiring +5 volts to pin 9 on that. but, not having to fuss with the software was a nice touch, i thought that might come in handy when switching devices... i might as well give it a shot.
but i had a ton of trouble getting the device to communicate --so frustrated, i nearly returned it! after pairing things up (pretty finicky there, really only pairs to one device at a time), it was relaying data from the home vision controller, but not transmitting.
after some detective work, i discovered that the gbs301 implements the entire rs-232 spec. the gbs301 waits for the CTS (clear to send) channel to signal +5v, then send data. however, just about every device i have only implements "3-wire" serial communication, just Rx, Tx, and ground --(receive, transmit, ground), and doesn't bother with CTS/RTS (clear to send, ready to send).
i can't actually fault iogear here --the gbs301 follows the serial spec! plus, their support line sent me a mod for the device. plus points there, good follow through. i think they heard this problem a bunch, had the a document already prep'd.
the fix is to bridge pins 7 & 8, the CTS and RTS lines --sending the RTS signal back to the CTS line. essentially if a device is waiting for the CTS line, it almost always also sends power to the RTS line. just be careful *not* to bridge the lines between devices, where both actually power the RTS line!
so, with any device that doesn't implement CTS/RTS, the gbs301 will never actually transmit data, it stops traffic right there. whereas the new homevision 'pro' models ship with a mod bridging CTS line back to RTS, my standard (older) version did not.
basically, it appeared like i could not send data, as if homevision wasn't listening at all.
i bought the parts but haven't bothered to assemble it... in the mean time, i took a tiny wire, plus a little solder, and bridged pins 7 and 8 on the homevision board itself (underside of the pcb board, adjacent pins, were easy to reach, middle two in the row of 4). that's great for now.
i'll still need my custom adapter, if i hook up anything like a gps --without having to fuss with that internal CTS/RTS pin mod. oh minor point... the baud rate on the gbs301 in pretty finicky --it must be set to the same baud rate as the device you're connecting.
you can invoke hyperterminal to swap modes on teh gbs301 there (first two seconds after powering up, hit keys "AT" --that gets you in the config screen). since 4800bps isn't in the range you can set externally, using the nmea 4800 gps protocol will require this extra step. so, a little extra to fuss with there, but you can do it.
my to changes to this product would be switch accessible 4800 baud mode (for the common nmea 4800 gps protocol). and then, add one switch for '3 wire mode' (no mods!).
oh, i'd also make it able to pair with more than just one device. while binding to one device makes it safer (won't unbind till you physically reset it), that makes it tougher to use. i can't swap laptops and still connect to the device, etc.
now, i'd consider getting a ethernet-serial adapter, and maybe hook up wireless up there --this would let any computer on my net connect up to the device... 'course all that comes, with a much higher price tag.
other links: gbs-301 manual
Interesting, thanks for the info. I actually tried a similar setup with a serial Bluetooth adapter from www.usconverters.com
Posted by Jack at November 4, 2010 05:21 AM
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