Hi! We see you’re using an ad-blocker. We’re fine with that and won’t stop you visiting the site.
But as we’re losing ad-revenue from this then why not make a donation towards website running costs?. Or you could disable your ad-blocker for this site. We think you’ll find our adverts are not overbearing!
Joined: Jun 17, 2004 Posts: 20 Location: Northumberland
Posted: Thu Jun 17, 2004 5:51 pm Post subject: 'Isolated' spliter cables
Hi,
Not sure where to post this, so here seems as good as any.
Also apologies for the length, but it's a little technical.
I have an intercom system on my motorcycle which I use to talk to my pillion passenger and also accept telephone calls. I also have a PDA (Dell Axim) running TomTom 3. I want to add the voice output from the PDA into the intercom system.
The intercom system has two inputs. One for phone/GPS and another for music. The idea is that any signal comming in via the music input will be muted whenever a signal is received via the phone/GPS input.
The intercom manufacturer sells a special 'splitter' cable with a built-in 'isolator' or 'filter' to allow both the GPS and phone to share the same intercom input channel. The input to the intercom system is a standard 3.5mm sterio audio connector. This special lead costs £30 and was apparently originaly developed for the Garmain StreetPilot III.
My question is, does anyone know what the issues are in this scenario and what components/wiring is likely to be in this special lead?
If it helps, both the PDA and the Intercom are powered by the bike electrics so will share a common ground/earth etc.
For now, I am simply going to feed the GPS audio into the music input and take a (very small) risk that I may miss a GPS instruction if I am currently receiving a telephone call.
Joined: Apr 11, 2004 Posts: 26 Location: Kent - UK
Posted: Fri Jun 18, 2004 8:06 pm Post subject: Re: 'Isolated' spliter cables
glennk wrote:
For now, I am simply going to feed the GPS audio into the music input and take a (very small) risk that I may miss a GPS instruction if I am currently receiving a telephone call.
Hi glennk. The quick answer is - yes good idea mate.
The long answer is....It's an audio fact that it's best not to directly couple 2 audio outputs directly together, normally you 'buffer' them with an amplifier or at least some resistance. - Thats what the isolator is for (just like 2 inputs on a mixing desk).
The phone and the PDA have LOW OUTPUT impedances (which can be regarded as resistance) and the intercom has a HIGH INPUT impedance. In this way very little current is drawn from the phone or PDA when they are individually feeding the intercom.
The isolation unit is there because if you couple the phone and PDA directly together they will both be 'looking' at each other's low impedance which will cause alot more current to be drawn - there is a risk of serious audio distortion or even that you might damage the output stage of either unit. It might be OK, but I wouldn't risk it.
Hope this helps
John _________________ ipac 2210, Integral 128Mb, Haicom 303E CF (& TT wired), Fugawi, TT3 & POI Warner
Nuvi 610T on my motorbike
Tomtom 720 in my car
Posted: Today Post subject: Pocket GPS Advertising
We see you’re using an ad-blocker. We’re fine with that and won’t stop you visiting the site.
Have you considered making a donation towards website running costs?. Or you could disable your ad-blocker for this site. We think you’ll find our adverts are not overbearing!
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum
Or you could disable your ad-blocker for this site. We think you’ll find our adverts are not overbearing!
Hi! We see you’re using an ad-blocker. We’re fine with that and won’t stop you visiting the site.
But as we’re losing ad-revenue from this then why not make a donation towards website running costs?. Or you could disable your ad-blocker for this site. We think you’ll find our adverts are not overbearing!
Forum FAQ
Search
Usergroups
Profile
Log in for private messages
Log in
) comments greatfully received.
