Introduction: Universal Mini OMTP ↔ CTIA Adapter - Convertendo
If you happen to have either some old earphones or mobile phones lying around, you might have noticed that the old earphones aren't compatible with the current phones and the old phones don't support the newer earphones. That's because older accessories were based on a different TRRS jack wiring standard known as "OMTP Standard" while nowadays, a new wiring standard known as "CTIA Standard" is being implemented in our accessories. The pinouts for each standard have been posted above.
That's enough for the explanation, now back onto the topic!
So what Convertendo simply does is the interchanging of SLEEVEand RING-2 poles of the inserted TRRS jack, because only their wires(MIC and GND) are different in the above mentioned wiring standards. The TIP and RING-1 poles are left untouched. Just to be clear, this adapter won't, in any way, do any modifications to your earphone. All it does is take the SLEEVE and RING-2 poles from the earphone jack though the Female TRRS jack, reverse the poles at the switch and send the switched poles to the Male TRRS jack. That's what make this project very convenient and clean. After making this and inserting your earphones in it, they will become compatible with every phone there is!
Step 1: Gather Around Some Stuff
For making this project, you require the following stuff.
1. A "6 Pin Push Switch" a.k.a. "Mini DPDT Push Switch".
2. A TRRS Male Jack.
3. A TRRS Female Jack.
I happened to have both, TRRS Male (salvaged from a non-working earphone) and Female(salvaged from a mobile phone) jacks lying around. But I wouldn't recommend their usage. You could buy a TRRS Male to Female Extension of considerable length for this job. Then simply cut it in half and voila! you've got your male and female TRRS jacks for making this project.
4. A TRRS Male to Female Extender.
If you plan to buy this, then don't buy the above two jacks for this will substitute them. You can buy it from here.
5. Heat Shrink Tubes:
Their usage is only for cleanliness' sake and they aren't that important. But still, if you do want to use them. Here's what you need:
- 10mm tube ≈ 1 cm.
- 2mm or 1mm tube ≈ 0.5 cm.
6. Some wire.
You might already have it. In my case, I used enamelled wire, which is used in earphones, because it occupies very less space and doesn't require any insulation work.
1. Hot Glue Gun, and
2. Soldering Iron.
That's all for the requirements.
Step 2: Doing the Switch Connections
Pick up the switch and trim its pins. After trimming them, bend them inwards carefully as done in the pictures.
The connections are to be made according to the schematic posted in the "Requirements" step. For clearer interpretation, I have added another picture of the wiring above. For this step, only interconnect the diagonal pins. The remaining two pins will be wired later ahead.
Step 3: Putting on the Heat Shrink Tube
Cut a 10mm heat shrink tube about the size of the switch and put it on the switch, and make two holes on opposite sides as shown in the picture. The hole we have currently made is for the wires of male and female TRRS jacks.
Step 4: Wiring the TRRS Male and Female Jacks
The Male Jack:
Pick up the male jack and strip its ends. You should get four wires. Don't mind looking up for their colour codes because most Chinese manufacturers don't even bother about it. The best way to determine the wire poles is by removing the enamel insulation from the wire by dipping it in excess solder present on the soldering iron's tip. After the enamel has been removed and your wire looks silver in colour(due to solder), pick up the Continuity Tester, and find out which wire is connected to which pole. If you lack a continuity tester, you can alternatively check for 0 ohm resistance through a multi-meter.
My wires didn't follow the standard colour code for TRRS wiring. That's why it is always best to test the connections. After the wire connections are determined, note them down.
The Female Jack:
If you have used a female TRRS jack like mine, you'll need to add wires to it, otherwise if you're using the TRRS extension's female jack then you'll just have to determine the wire connections. The process will be same as in the male jack.
I'll proceed with this step considering you have a female TRRS jack just like mine.
Gather any wire which contains 4 wires. I happened to have some leftover of my earphone's enamelled wires. I soldered the ends to remove the enamel and then connected each pin of the jack with a wire randomly. Now all that's left for you is to determine which wire connects to which pin of the inserted TRRS male jack. To do it, insert the above stripped male jack into the female socket and start comparing the wire connections using a Continuity Tester. Note down the wire connections for later reference.
Step 5: Connecting the Jacks With the Switch
After determining the wires clearly and ensuring that no two wires are interconnected, you can proceed further.
Remember the two holes you made in the beginning? They were for this moment. Yep, that's right! For being a passageway for the jack wires. That being said, insert the wire of the male jack through a hole and solder the SLEEVE and RING-2 wires of your male jack to the switch(leave the other two wires untouched) as shown in the above picture.
After that, insert the female jack wire into the heat shrink tube hole as well. You may refer to the above picture. Then, interconnect the audio wires and after that, solder the remaining female jack wires to the switch as well.
That does it for the technical part of this project. Now it is in working condition. Check whether it is working by plugging your earphone to your phone through Convertendo. If it sounds alright, then it's working, if it doesn't, unplug Convertendo from your phone, push the switch to change adapter mode and re-insert it into your phone. Now it should sound normally. If you still face any problem, refer to the schematic and check your wiring.
After testing it, let's proceed with making it durable! Move the 10mm heat shrink tube up the wire to the switch's end and cover it. Be careful while arranging the wires. Then heat the tube and it should look as shown above.
If you want to, you can also move a step ahead and insulate the female jack as well. Picture's above.
This isn't necessary for those who used the TRRS extender to get the Female jack.
Step 6: Strengthening the Solder Joints
Step 7: Congratulations!
Congratulations! Now your Convertendo is finished, and now you can go on and enjoy listening to music across all devices without worrying about compatibility.
If you have found this instructable helpful, please support me by reopening the shortened links twice or thrice. That's all for this instructable! If you have any doubt, feel free to comment.
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Thanks to Ashish Choudhary for lending his camera.
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