Running I2C on Pro Micro (4) - TRRS Connection
In this fourth article of the series, we will connect the breadboard using a TRRS cable. This will enable us to connect distant breadboards with a single cable, increasing independence and simplifying wiring.
Prerequisites
TRRS cable is a four-pole (four independent wiring) cable. The acronym TRRS comes from the first letter of Tip, Ring, and Sleeve, and is commonly used in audio equipment that requires a microphone. A similar cable is the TRS cable, which is a three-pole cable. It is often used for unbalanced stereo connections[1], which is frequently used in general audio equipment, so if you buy a similar cable without thinking, you may end up with a TRS cable by mistake.
So, why use a TRRS cable? You may think, "But we were using I2C connections until now?" However, there is a hint in the previous articles. Think about it like a mystery novel.
Why use I2C
In the previous articles, we connected the breadboards using I2C connections. However, to operate the IC, we needed not only the SDA and SCL signals but also the power supply VCC and GND.
Therefore, since we need four signal lines to operate the IC, we use a TRRS cable. There are several types of cables that meet this requirement, but the TRRS cable is widely used as an I2C cable due to its ease of use and the convenience of its connectors.
Parts needed
This time, we will add a TRRS jack to both the Pro Micro side and the IO Expander side.
- MJ-4PP-9 (3.5mm TRRS jack) x2
- PJ-320A is also possible. Any 3.5mm four-pole jack will work.
- 3.5mm TRRS cable x1
- Note that four-pole (TRRS) cables are rare. A good deal can be found for around 220 yen for a 0.15m cable (Sengoku Net)
Parts used so far
- Breadboard (BB-801 or similar) x1
- Pro Micro + pin header x1
- Reset switch x1
- Pin input switch x1
- Jumper wires x many
- Cable to connect Pro Micro to PC
- MCP23017 x1
- 1kΩ resistors x2
- Breadboard (BB-801 or similar) x1
- If you want to separate the breadboards. If you can fit everything on one breadboard, that's fine too.
Configuration
Preparation
Unfortunately, the MJ-4PP-9 jack cannot be inserted into the breadboard. Therefore, we will solder jumper wires to each leg of the jack and insert them into the breadboard.
Wiring diagram
We assigned the four-pole jack as follows. After researching, it seems that the assignment of the pins is not strictly defined, except for GND. As long as the assignment is consistent within the board, it's okay. However, if the assignment is different between the two connected devices, it may not work or cause a short circuit.
The assignment is okay as long as it's consistent within the board
We will connect the breadboards using the TRRS jack, similar to how we connected them using cables before. The independence has increased, and the wiring looks neater.
Actual result: Cable connection
Operation check
If the TRRS cable is connected correctly and the behavior is the same as before, it's a success If it doesn't work, make sure the cable is inserted all the way into the jack.
Summary
We have connected two distant breadboards, making it look more like a real project. Next time, we will connect three devices and try a daisy chain. From here, the strengths of I2C will become apparent.
This may not be familiar to those who are not familiar with audio. ↩︎
