Hacking Hard Buttons on Jaguar SatNav

Hello All,

This is my first post, just signed up new to this forum. I'm a regular on some other forums for Jaguar cars, where we've been doing a lot of mods & retrofit work, now im looking for some help regarding a momentary-switch to latching-relay circuit, with a twist.

This is a great forum, lots of info here. Though I did a search but only found something similar using rocker switches, not momentary inputs. And it was a more basic setup using relays, whereas this requires a voltage-free input since the momentary switches are already connected to another device.

The Jaguar X-Type, S-Type & XJ X350 use a Denso touchscreen SatNav, & it's popular to use a Video Interface Module (such as the NavTool NAVRGB) to bring video onto the touchscreen. This works fine, but you need an external switch to turn the NavTool on & off. The factory SatNav looks like this;

http://jaguar.bttlxe.com/xtype/projects/satnav/Finished!

There are five separate hard buttons around the screen to select menu's & functions in the touchscreen;

Left side, from top is Audio, Phone, Climate. Right side has Nav and Menu. These are momentary switches.

A single press of those buttons takes you to the relevant screen. Pressing the same button again does nothing.

What I'm looking to do is build some sort of circuit, so that two presses of the Nav button closes the input circuit to the NavTool interface to bring up the video. A third press of the Nav button opens the circuit to the NavTool interface. At the same time it would be great, if a press on any of the other four hard buttons, would also open the circuit to the NavTool. Since the screen will change to whatever button has been pressed.

I imagine we'd need something with isolated inputs, since we don't want to introduce any voltage to the SatNav electronics via the switch. Just something that will see if the circuit is open or closed only. Also needs to count how many presses, and close a contact accordingly. Same contact would also need an additional 4x isolated inputs, to open the circuit only, multiple presses on the other buttons won't do anything.

So, has anyone seen anything like this available as a kit? Or will it have to be made from scratch?

Could someone point me in the right direction of how to make this little gizmo?

Many thanks.

Currently messing around with Jaguar's...

Sorry, seems the pic was too big, let's try this one....

http://dl.dropbox.com/u/11575086/29012011453-S.jpg

Currently messing around with Jaguar's...

The first thing you need to figure out is how the actual buttons work. If they switch to ground it will be easier then if they are on a communication bus. With there being so few buttons it would be plausible that they are direct (-) inputs, but at the same time I wouldn't be surprised if they were on a bus - the only way to figure this out is to pull the system apart and use a volt meter to determine if one side of each switch is grounded. Once you determine this then you can figure out what it will take to interface with all the buttons. A "one, two, three" type button detection will most likely require more advanced electronics. You are right about isolating all the inputs if you want to use them all - they will need to stay separated so that everything continues to work correctly.Kevin Pierson

Thanks Kevin,

I'm waiting to get my hands on a scrapped screen to pull apart, as you can imagine I'm not keen to pull the perfectly good unit out of my car & experiment on it. I understand what you are saying about the difference between a grounded & BUS setup, though I thought it was better to stay out of the SatNav electronics completely, just piggy back two leads from the switch & go straight into an optical isolator. Maybe i'm thinking too simply about it? It's been a long time since I played around at this level....

Currently messing around with Jaguar's...

I HIGHLY doubt that they will be controlled by ground signal.  Generally there are 4 outputs and 4 inputs on the microprocessor.  The 4 outputs will have slightly different pulses on them.  The inputs look and determine which of the 4 outputs gets sent back to that particular input.  This is how it determines which function to perform.