I am using an NPN transistor to pull down PTT, controlled by the parallel
port. I am not using an optoisolator for PTT, nor am I using isolating
transformers for the audio, because I am callous and evil.
It looks like this IIRC:
PC MIC ---------------------------------------------------- HT SPK
100n
PC SPK ------||---+---------------------------------------- HT MIC
|
<
< 2k2
<
10k |
LPT.0 --vvv-----K NPN
|
GND -----------+---------------------------------------- GND
I could probably have found a web page with a better diagram of this circuit.
Anyway, the whole thing cost a couple of dollars, and it worked. The
laptop is an old Thinkpad 600E (dicky sound drivers), and I am using a
cheap Chinese HT, so I'm not in the hole for much if it goes bang.
What I *really* want to do is find a cheap USB audio adaptor with a
controllable LED on it. They are available, but I don't actually have one
to play with. I am sure it would be possible to hack the driver so that
the LED could be used to drive PTT, then you would have a single unit to
connect a radio to the PC.
73,
Andrew
ZL3AME
On Sun, December 7, 2008 04:33, Alan Crosswell wrote:
> I'm curious what hardware interfaces people are using these days for PTT
> for soundmodem? So far, the old computers I use for aprsdigi are still old
> enough to have a parallel port so I use a 2n2222 PTT setup, but pretty
> soon that's no longer going to be the case. A long time ago I tried the
> VOX-based PTT ckt but was not successful with it.
> 73 de N2YGK
>
>
>
> Gary Huntress wrote:
>
>> Thanks to everyone for all the replies. I definitely needed to
>> change the permissions on the xastir binary, that helped. The
>> permissions on /dev/soundmodem0 were already 777 so I didn't do anything
>> with that.
>>
>> FWIW, on the same box, I'm running an XP virtual machine with
>> soundmodem and it is receiving. I shut down that VM and switch to
>> Ubuntu and I'm not
>> getting anything. I have to assume it's something with ALSA, the
>> various capture devices, or mixer settings.
>>
>> Thanks for the help. I may just switch to a hardware TNC if I can
>> find a decent one supported by linux!
>>
>> Gary H.
>> KB1QOJ
>>
>>
>>
>> On Sat, Dec 6, 2008 at 2:49 AM, Andrew Errington <
>> [EMAIL PROTECTED]> wrote:
>>
>>
>>>> I suspect if a few of us who have set it up before got together and
>>>> wrote a step-by-step on the Wiki, we'd be able to keep it up to
>>>> date from then on. I've got many years under my belt with AX.25 on
>>>> Linux (KISS
>>>> TNC's attached to real serial ports). I've only done
>>>> soundmodem setups a few times and never set up transmit with it.
>>>>
>>> Crikey. I thought I was way behind the curve with a lot of catching
>>> up to do! I've been busy in the last couple of weeks.
>>>
>>> I built a radio cable using the parallel port to control PTT and I
>>> was very pleased when it actually worked. There were three issues I
>>> had to deal with:
>>>
>>> 1) Permissions on the soundmodem0 device. I mentioned how I solved
>>> this, but Curt has give the correct answer, which I will have to do. 2)
>>> I was using a handheld radio with PTT combined with the mic. signal.
>>> I
>>> had to put a capacitor in the line from the PC audio out otherwise PTT
>>> just pulled the audio signal straight to ground (many PTT circuits
>>> don't show this). 3) Tweaking the sound mixer settings to coax the
>>> audio driver to work properly. For some reason the mic. input on the
>>> laptop doesn't work unless I turn the mic. boost switch on then off
>>> again. I knew this was an issue on this laptop as I have the same
>>> problem with Skype.
>>>
>>> After that it Just Worked. Thanks to the XASTIR dev. team for much
>>> coolness.
>>>
>>> 73,
>>>
>>>
>>> Andrew
>>> ZL3AME
>>>
>>>
>>> _______________________________________________
>>> Xastir mailing list
>>> [email protected]
>>> http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
>>>
>>>
>>>
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>>
>>
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