alerting, and I'm using the RS232 port option to trigger a
relay. I can speak to this - I was one of the people who
originally suggested this option be built into the system.
I admit that when using the system for just straight alerts
I've never been a big fan of passing audio through the sound
card. As you have found this can degrade audio quality, it
also can introduce delay into the audio chain. If you're
using a cheap sound card, especially a consumer grade sound
card, it can just sound bad (in my opinion). And if the
power fails on the box then you are silent to air.
Using a relay will eliminate the delay when you are "live to
air". It'll also eliminate the possibility for the box to
cause audio degradation. If the power fails on the box
it'll still pass audio through by default.
What happens - when an alert comes in it'll first trigger a
high voltage on one of the serial port output control lines
(sorry - I'm not at home as I type this, I don't recall
which control line it is - I'll have to check once I get to
where my notes are). As long as the alert is playing then
the voltage will remain high. Once the alert is done then
the voltage on that control line goes back to low.
Simply build a circuit to have that control line switch a
relay box. Wire up your audio to normally pass through the
relays. Wire up the audio output from your OpenBroadcaster
box to the normally open (NO) side of the relay. When the
relay is triggered it'll connect the OpenBroadcaster audio
output to the output going to the transmitter. When the
relay is turned off it'll restore your audio.
It is relatively easy to build your own relay circuit,
especially if you are an analog plant. Assuming the system
you are running your OpenBroadcaster player on has a serial
port then all you need is a 4 channel relay, a power supply,
a connector to hook to your serial port, a project box to
put it all in, some time and knowledge to be able to wire
the whole thing up and build the thing. I think I also
needed a little transistor in the trigger circuit to make
mine work. I built the relay unit we're using at CJAM-FM
for about $30 worth of parts and it works like a charm
(although I admit that I had some of the parts in my parts
bin so I didn't have to purchase them).
Any of the 4 channel relay boards for a Raspberry PI or
Arduino should work, something like the following should
work (I admit that's not the board I used, I can't vouch for
it but the reviews look good):
You'll also need a 5 volt power supply - it is possible to
pull power from the computer's power supply itself if you
know what you're doing, or you could just get a wall-wart.
Cell phone USB chargers are 5 volts and generally have
enough available current to drive one of these boards, so
that's a viable option.
I can send another note with more details. Openbroadcaster
has some pictures of a unit that was made in Waterloo as an
idea of what I'm talking about.
Bottom line is - the RS232 relay option does work well and
if you have some technical knowledge it can be done for
relatively low cost.
We have a unique setup. Our broadcast engineer works for the commercial stations in town and he found that the NAAD box they bought can send DTMF tones before the alert. So we have a radio permanently tuned to one of those stations with a DTMF decoder/relay device that cuts to their signal for the alert and then cuts back.