In short, I'm trying to increase the voltage going to one of the pins in a Euro SCART AV lead from around 2.3V to 7V-9V. The pin only carries an on/off voltage so my idea is to use an external supply (a 9V battery) to boost the signal. However, I don't want the battery to always be on and don't want to turn it on/off manually.

I am completely new to electronics (appart from some long-forgotten Physics from high school) so my efforts sofar have been inept at best. Here's the problem in more detail:

I plan to make an adaptor which sits between the (male) SCART plug and my TV's (female) socket. The adaptor itself would have a female socket, to accept the source plug and a male plug to attach to the TV.

SCART Socket.
Pin 8 = "channel selector" (2.3V when the source is "on", relative to pin 17 - this needs to increase to ~7V)
Pin 17 = (Video)Ground

All signals/pins would be wired to pass straight through except pin 8 (and pin 17? - I don't know). I read up a little last night and made a circuit with an NPN transistor (acting as a switch) this morning. I was trying to get the 2.3V to allow the 9V to flow through the collecter & emitter which I them connected to the appropriate pins connecting to the TV.

It almost worked except that the current flowed through the collecter/emitter even when the 2.3V was not present i.e. when the source was turned off.

Does anyone know of: the correct way of setting up the circuit; an easier way to achieve the same result (I know I can manually select the channel on my TV but where's the fun in that ) or a pre-made device which boosts the voltage on pin 8 of a Euro-SCART?

Any help is much appreciated.

Thanks
Dan

 

I've just found something on the web about a step-up converter/boost converter. Would this be suitable?

Dan

 

Originally posted by halfacandan@Apr 11 2006, 05:12 AM
I've just found something on the web about a step-up converter/boost converter. Would this be suitable?

Dan

[post=16048]Quoted post[/post]​

First question is why do you need to do this?

This site http://www.bnoack.com/data/cables/scart-pinout.html show pin 8 as being 9.5V to 12V for a high and 0V to 2V for a low. This would put your 7V in a neutral zone and may not do anything.

Also the step up/boost convertor may work but can't really say as we have no idea what it is. An ignition coil on a car is technically a step up convertor. If you can supply a schematic or a link to it it would help.

Overall your idea of a 9V battery should work. And if the cct is design properly then there will be no current drain from the battery when it is off.

 

Originally posted by windoze killa@Apr 10 2006, 11:05 PM
First question is why do you need to do this?

I think each TV varies slightly. The 2.3V volts doesn't do anything with my TV. When I had the battery linked up, it worked fine. 9.5V to 12V would be ideal.

Also the step up/boost convertor may work but can't really say as we have no idea what it is. An ignition coil on a car is technically a step up convertor. If you can supply a schematic or a link to it it would help.

Sorry, I thought it was a standard electronic principal There seem to be lots of variations on it but this one seems simplest.

Thanks for your help.
Dan

 

I just read that link that you gave me and describes what I am experiencing:

High (9.5-12V) AVmode
Low (0-2V) TVmode

A low signal won't switch a TV into AV mode (which is what I want).

Dan

 

Originally posted by halfacandan@Apr 11 2006, 08:41 PM
I just read that link that you gave me and describes what I am experiencing:

High (9.5-12V) AVmode
Low (0-2V) TVmode

A low signal won't switch a TV into AV mode (which is what I want).

Dan

[post=16092]Quoted post[/post]​

And what is your voltage when the signal is high?
Just in case you didn´t understand, the VCR or whatever can send two signals - High meaning AV mode and Low meaning TV mode.
To me it seems that it always sends low and that´s the real problem. You should find how to make it send the high signal, instead of trying to get high from low.

Or you want to make it High->TV mode and Low->AV mode?

 

Originally posted by kubeek@Apr 11 2006, 07:56 PM
And what is your voltage when the signal is high?
Just in case you didn´t understand, the VCR or whatever can send two signals - High meaning AV mode and Low meaning TV mode.
To me it seems that it always sends low and that´s the real problem. You should find how to make it send the high signal, instead of trying to get high from low.

Or you want to make it High->TV mode and Low->AV mode?

[post=16096]Quoted post[/post]​

I reread my last post an realised that it wasn't too clear. I realise that my TV sees ~2V as low and ~9+V as High. The source (a games console) outputs ~2V when on (high) and (as far as I know) it can't be made to output more than that. It is an american model which isn't made to use a EURO SCART plug hence the tiny 2V output to pin 8 instead of the necessary 9V.

I think that my options are to directly raise the 2V to 9V or use a switch/external 9V source circuit. However, I don't know enough about electronics to tell which of these is easier/feasbile.

Thanks
Dan

 

The site I linked to above says:

You can make an ultra simple 1.5v to 9v regulated stepup converter by using a TL496 IC, a coil and a capacitor

There's not circuit diagram though so I'm stuck. I found the TL496's datasheet (here) but it only shows a circuit for use in an AC system. It seemed to suggest that the chip is made to be used with batteries os sources of 2-3V output, raising them to 9v.

Am I on the right lines now?


Thanks
Dan

 

I think i just found a pre-made version of what I am looking for

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?Vie...mMakeTrack=true

Dan