Hello world, today I am bringing you another instructable at the request of another member.
I recently made an instructable about booting the Raspberry Pi from a usb flash drive (Boot the Raspberry Pi from USB). In that instructable I had my RCA connection "jerry-rigged" to work fast to display on a small CRT television to test that my method actually worked. Member Mason Wright asked if I could post a tutorial on how I connected the monitor using RCA with the Raspberry Pi 2, along with a few others who had questions regarding the deal with the alligator clips on the Raspberry Pi. I figured I'm on summer vacation, so why not give the people what they want?
What you need is:
1x - Raspberry Pi 2 (or I think maybe B+)
2x - Alligator clips
1x - RCA cable
1x - Monitor to connect to
Step 1: Raspberry Pi 2 TRRS Connection
Here I just give some info about the connection on the Raspberry Pi 2, feel free to skip this step if you don't care.
The audio jack on the Raspberry Pi 2 is one called a TRRS jack, which stands for Tip Ring Ring Sleeve. What this means is that it had four connections instead of the standard three that is common with normal audio applications. The TRRS jack is used on smartphones to provide audio as well as a microphone input, but on the Raspberry Pi 2, it provides audio as well as composite video.
By the diagram above, the farthest two connections are for audio, the closest is for video and the one in between is ground. The position of the video being closest to the jack housing, or farthest out in the female jack is critical for this method.
Step 2: The Raspberry Pi's Jack
If you take a look at the TRRS jack of the Raspberry Pi 2, you'll see that you can see a little metal prong which is very close to the opening of the jack. This little prong is the video output pin. It is close to the outside since on the previous diagram, the video pin on the male jack was also in the same place.
This makes wiring it up very easy since all you have to do is connect an alligator clip to that little pin. It's very close to the opening so it doesn't even have to go in very far.
But word of caution, if you do put it too far in, then you won't get any video since it might short with ground or an audio pin. Shorting with ground should not damage the Raspberry Pi since a standard TRS (yes, only one R this time) will short the video and ground, so safety measures have been implemented to prevent damage. BUT!!! In the rare event that your Raspberry Pi does get damaged by shorting video with something else, it is IN NO WAY MY FAULT since I am not forcing you to do this (and I see no reason why anything would get damaged).
Step 3: Connecting the Pi
Here you can see a picture of my Raspberry Pi 2 with an alligator clip in the audio jack.
Here is also where I got a few questions. Some people were asking why I had a black alligator clip connected to the HDMI casing, and they speculated that it was for static discharge purposes or something. It is actually used as a ground connection for the video signal since composite video uses one signal wire and one ground wire. You can use anything that is grounded on the Pi (HDMI casing, ethernet casing, USB casing, gpio ground, circuit board ground, etc) as long as it is connected to ground. I just chose HDMI since connecting to that case would make the black alligator clip face the same direction as the white one (I like symmetry :p ).
In the second picture, you can see the white alligator clip connected to the signal pin of an RCA connector and the black clip connected to the grounding part of the RCA connector. The other end of the RCA cable went into this little portable CRT tv I have that can also accept composite video input.
Step 4: Alternate Method
For those who are eccentric or need their Pi for a super compact, flat embedded project, I have just the thing.
If you need/want to solder your video connection, I have provided a picture of the underside of the Raspberry Pi 2 and have circled the video pin in red. If you solder one wire to any grounding point, and another to the video pin circled in red, then you can get video out in a very compact way.
I originally did something similar where I used an alligator clip on the HDMI casing and one clip to the little tab barely sticking through the solder to get my video. This was before I figured out I could do it straight through the TRRS jack.