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Old 14th August 2009, 15:04   #1
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Thumbs up Inspired DIY bluetooth handsfree for DXZ 785USB

With full credits to Shreyas for his inspiration, here is my DIY. I had some time on hand and so I wrote this up right now. Unfortunately, as I have already assembled everything, I do not have detailed pictures. Will still be posting as many as I can separately soon.

Mods - if this post does not belong here, please shift it to the appropriate location.

Stuff needed:

A Bluetooth mono handsfree – I chose ‘Enter’ brand because it was cheap and is still fairly good quality – Cost: Rs. 650

Cellphone with Bluetooth functionality – needless to say!

A thin gauge audio wire – I used one from an earbud type headphone. The wires are thin and easier to route inside the small Bluetooth device casing – Cost: Rs.0 (I had a spare headphone)

An audio cable – Female 3.5mm socket at one end and male RCA connectors at the other. Select the length according to your setup – Cost: Rs. 30

A car cigarette lighter adaptor with USB power port – I had one spare from a portable car FM transmitter I used long ago.

Soldering Iron

Wire sleeves

Multimeter (if available, for continuity checking) - You can even do without this.

Hacksaw blade

Pincers

Cable ties

Insulation tape

A piece of adhesive backed Velcro strip

Time and patience

Steps:

1. Pair your cellphone with the Bluetooth you have bought. Test and make sure the sound quality is good enough.

2. Prepare the Bluetooth device for modifications – using the pincers or a really flathead screwdriver, carefully pry open the Bluetooth device casing. Start from the end where the microphone is situated and pry upwards. It has 4 retaining snap-ons inside. Be careful not to break them while opening. Do not push the pincers too far into the casing or you may damage the circuit/electronics inside.

3. Once opened, locate the two wires connecting the tiny speaker to the circuit board (red and black). Snip off the wires as close to the speaker as possible so that you have around 8-10mm of wires to play with. Be very careful lest you accidentally pull off the soldered connections on the circuit board. I did and then I had to really struggle with soldering on the board itself (lack of proper equipment). Also, the electronics are very sensitive and may fry if you are a novice trying to directly solder something on the board.

4. The speaker is glued into the casing’s bottom half. With a little force, try to rotate the speaker while holding the casing. The glue should give way and you can pull the speaker out of the casing. This makes it easier to mount the completed setup on a flat surface later. The speaker protruding out is a problem otherwise.

5. Using a hacksaw blade cut a tiny notch into the bottom half of the casing towards the back (where the power connector is). Take care to cut the notch where the power connector DOES NOT mate while assembling. We will route the audio cable through this notch.

6. Snip off the earbud headphone speakers from the spare set you have so that you are left with an audio cable with a 3.5mm male connector at one end and free wires at the other. This being a stereo connector, has a ‘common’ and ‘channel’ strand each for two channels. You can combine the channels later.

7. Select one of these snipped wire ends. Slip in the wire sleeves before soldering. Strip off the insulation and with the best of your electronics’ hobbyist skills; solder the ends to the ones you exposed from the Bluetooth in step 3. Slip back the sleeves onto the joint and heat-shrink them in place. If you are not comfortable with this process, please go to a good electronics repair guy in your area and ask for help.

8. Now route this wire ‘around’ the battery in the device (the big shiny thing), pushing it under the retaining notches, behind the volume control buttons and out from the back. The idea is to make sure that your joint will be securely held and not come off from inside later.

9. Assemble the casing together making sure that your wire is coming out of the back through the notch you cut earlier and not forgetting the tiny plastic for the volume control buttons. I did and then I had to open the whole thing up again.

10. Strictly Optional – strip the wire a few inches from the Bluetooth device. Strip (remove the insulation) – do not cut. You can then splice the second ‘channel’ wire end into this making sure the ‘common’ gets connected to ‘common’. This will essentially feed the same signal into both channels. Insulate with wire sleeves as necessary.

11. At this point, I turned on the Bluetooth and tested my connections using a multimeter and making a call. There would be a tiny fluctuating voltage at the 3.5mm male jack between the common and the channel. Don’t worry if you can’t do this step. Just keep your fingers crossed instead!

12. The Bluetooth comes with a charging cable that plugs into a USB port for charging. Connect the charging cable to the device and tape your new audio wire with the power cable for neatness.

13. Take out your HU from the facia and locate the Aux connectors. Read the HU manual to locate them. Connect the RCA cable (with a 3.5mm female jack) to the Aux.

14. Plan your mounting location. You will have to route and secure the wires accordingly. I’ve seen that a location closer to the center of the car on the dash works best (gives minimal echoes in the final result). I decided on mounting the Bluetooth device on the left side of the steering column cover. This way it is closer to the center, not very prominent and the buttons are also accessible easily.

15. I ran the Aux cable from the back of my HU into the glove box (where my USB source cable with the thumb drive resides). This way I can use the Aux for connecting any other device if ever needed.

16. I ran the Bluetooth charging cable from the side of the steering column, inside the dash and brought it out right under the car cigarette lighter. The audio cable was routed from the side of the steering column, inside the dash, behind the HU and came out into the glove box. Cable ties were used to keep things in place. It required a fair amount of twisting and turning in unnatural positions to get this done!

17. Connect the 3.5mm pin to the Aux cable in the glove box. Using a strip of adhesive Velcro, mount the Bluetooth device at the designated location.

18. Reassemble the HU and the facia and fire things up.

19. Switch to Aux as the input source, switch the Bluetooth on and make a few calls to determine the volume levels you would need and setting the Aux input sensitivity.

You might notice crackling sounds in the speakers when you plug in the charging cable into the cigarette lighter USB adaptor. If this happens, disconnect the Bluetooth device from the Aux cable in the glove box before connecting the charger.

Now any time a call comes in on your phone, you can switch the source on the HU to Aux, hit the ‘Call’ button on the Bluetooth and take the call. It might take a few tries for you to get used to this.

The DXZ 785USB comes with a telephone interrupt. However the Clarion car Bluetooth handsfree compatible with this HU has a separate cable that wires into the HU to trigger the interrupt. I’m exploring what that interrupt does. If I figure it out, I’ll update the thread with the mod. This will then enable us to take calls without the need to manually switch the source. The interrupt also mutes the HU when a phone call comes in.

Last edited by the_maassk : 14th August 2009 at 15:11.
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Old 14th August 2009, 17:14   #2
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Hey Man, As far as I know, when some current is fed to the tel interupt lead, it mutes the system. How much current? I dont know. (can we get more info about this from a clarion phone kit manual??)

Similar is the illumination lead, that will dim the HU display light when current is fed by connecting it to the heallight switch. In this case, its 12v. What you can do is use an DC adapter that has variable voltage selector and start passing the current. I'm a dumb fellow at electronics, dont know how far the crap I spoke will work out

And for the USB enabled HU, you can charge the headset using the USB port instead of the cigarette lighter. One hour charge used to last 2 days for me considering 3-4 hours of drive everyday

My usual statement:- Please dont forget pics

Last edited by shreyasma : 14th August 2009 at 17:16.
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Old 14th August 2009, 17:23   #3
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My opinion below:
(20 characters)

Quote:
Originally Posted by shreyasma View Post
Hey Man, As far as I know, when some current is fed to the tel interupt lead, it mutes the system. How much current? I dont know. (can we get more info about this from a clarion phone kit manual??)
Have looked at the manual already. Nothing in it.

Similar is the illumination lead, that will dim the HU display light when current is fed by connecting it to the heallight switch. In this case, its 12v. What you can do is use an DC adapter that has variable voltage selector and start passing the current. I'm a dumb fellow at electronics, dont know how far the crap I spoke will work out.
I'm sure the trigger is a voltage signal. Also, it has to be persistent until the phone call lasts. Too risky to try using a standard DC adapter. Let me try and get some equipment in place. Thankfully I have some resources.

And for the USB enabled HU, you can charge the headset using the USB port instead of the cigarette lighter. One hour charge used to last 2 days for me considering 3-4 hours of drive everyday
Yes, you can. But I have my USB drive with all my music connected to the USB port on the HU. Also, I would not risk a 2-port USB hub on that connection because the hard drive draws a good amount of power.

My usual statement:- Please dont forget pics
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Old 15th August 2009, 11:55   #4
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Quote:
Originally Posted by the_maassk
The DXZ 785USB comes with a telephone interrupt. However the Clarion car Bluetooth handsfree compatible with this HU has a separate cable that wires into the HU to trigger the interrupt. I’m exploring what that interrupt does. If I figure it out, I’ll update the thread with the mod. This will then enable us to take calls without the need to manually switch the source. The interrupt also mutes the HU when a phone call comes in.
I can help you a bit. When I was looking for a BT kit, I tried to find out the function of this "telephone interrupt" wire. If I got it right, this is how it works- when it is grounded, whatever being played is muted and source is automatically switched to aux-in. Only one of the channels is used for phone, left or right. You can set it appropriately as per your connections. When this wire is left open, HU resumes it's normal functionality. However, I am wondering how will you "generate" that signal? Car kits do have this features, but I don't think it makes any sense for BT headsets to have such output.

One easy way would be to put a switch that grounds or opens it (after doing due testing, don't take my words for it!) and mount it at a handy place. It won't be automatic as such, but pressing it manually would be much more convenient than fiddling with HU buttons located at he center of dash. Not to mention the chances of pressing eject instead of source button would be ruled out!

Last edited by Technocrat : 18th August 2009 at 15:58. Reason: Splitting the post across 2 threads.
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