[mythtv-users] USB to Serial Adapter cable for IR Blaster?

Gary Buhrmaster gary_buhrmaster at usa.net
Tue Mar 16 20:41:04 UTC 2010


On 03/16/2010 11:33 AM, Brent Meyer wrote:
> On Tue, Mar 16, 2010 at 7:58 AM, Ben Eisemann <ben at locojeeper.com> wrote:
>>
>> Has anyone had any success running the USB to Serial adapter cables?
>> I read (okay, skimmed) an article in Linux Journal about kernel driver
>> versions and it just made my head hurt.    Is there anything out there
>> that I can use?
>>
> 
> Unfortunately, serial IR blasters do not work with USB adapters. As I
> understand it, the serial blasters exploit a feature of the serial
> port that simply cannot be recreated by a USB adapter.

Simple serial IR blasters toggle a control line (DTR) with (more or less)
precise timing to control the IR signal.  It requires being
able to turn on/off the control line at around 38Khz in the low level
kernel serial driver with some precision.  *A* reason that sometimes
the simple serial blaster fail is because the kernel may be busy doing
something else, and does not get back to the driver as soon as needed
for the next transition.  A USB serial adapter is not designed to be
able to control the DTR line with that type of timing precision.
 
> A few months ago, I faced the same situation you're facing now. After
> spending too much time and money trying to get various solutions to
> work, I threw in the towel and bought a CommandIR mini. It's an
> expensive unit, but it works very well and was very easy to set up.
> It's definitely worth the price.

I looked into that, but found that they were out of stock, and
besides........
 
> You might also look into the IguanaWorks IR blaster, which is half the
> price. It seems like some people have been able to get it working
> pretty reliably.

The IguanaWorks IR blaster seems to work fine (I purchased
the 2 stereo jack model - 4 IR transmitter capability).  One
issue is that your distribution might not include lirc already
compiled with the IguanaWorks driver (while others include the
CommandIR driver), so you may need to rebuild lirc after
installing the IguanaWorks code (once the IguanaWorks 
headers are installed in the usual place, rebuilding should
include the driver via configure tests).

To make things cleaner in the long run I plan to use some
optoisolators to run the signals from the blaster to the
DTA units thanks to the ideas from others that have done
the same thing from tivo's to the DTAs.




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