Hi Stefan,
Unfortunately I haven't been able to come to any of the pi meetings but your project sounds very cool!
The USB to TTL plug you posted is long because it contains a FTDI chip to convert the signal, but you know the Pi has a perfectly good selection of built in gpio serial pins right? (Even if you're already using the dedicated p14/p15, the other pins are multipurpose)
For powering the Pi, you can actually wire the usb power directly through the 5v and GND pins on the pin header to conserve space. The pins are here: http://elinux.org/RPi_Low-level_peripherals#Power_pins for reference, and I'd recommend double checking before turning it on. One tutorial that has a diagram for direct power hookup is at http://learn.adafruit.com/light-painting-with-raspberry-pi/hardware (It uses a DC adapter but its the same for usb power, you could even build a tiny 9v to 5v regulator with a tutorial). If you want it to look nice and clean you can order a pi 2x13 header socket to solder everything to instead of directly to the pi pins (You might already be using some of these pins for serial comm sensors anyways), or you can use servo extension wires.
For getting power out of the usb battery device without using much space, you could order this: http://www.digikey.ca/product-detail/en/1001-010-01001/1175-1007-ND/3064738, which has 4 pins that should be easy to solder to.
For the Male to male RCA phono jack, it does indeed appear not to exist, but for the male to female the easiest source I found was http://www.amazon.ca/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywo.... Alternatively you might connect two of these: http://www.digikey.ca/product-detail/en/3501MX/SC1312-ND/1125424 together since they seem to take up almost no space (I'm not entirely sure how easy they are to solder to though...).
Parts aside, you mentioned you're putting a variety of sensors into the enclosure, you should test these in close proximity to the Pi first. The EM field will probably interfere with the compass, accelerometer and gyroscopes (if they are chip based) so you might want to shield the Pi or put them in a separate waterproof box.
P.s. Not sure if you've ordered from Digikey before but if not, make sure you order everything at once because the shipping is a $8 flat fee but arrives literally overnight.
Hope this was helpful! David Gaul
----- Original Message ----- From: "Stefan C. Kremer" skremer@uoguelph.ca To: pi-users@socs.uoguelph.ca Sent: Wednesday, June 12, 2013 5:56:37 PM Subject: [Pi-users] My Pi Project
Hi,
So a few weeks ago, I spoke to this group about my RaspberryPi project: an on-board sailing coach computer. The goal of this is to create a self-contained, battery powered, waterproof Pi equipped with GPS, Compass, Accelerometer and Gyroscopes.
This is a little project report/update for anyone who is interested as well as to see if anyone has any help with a couple of challenges that I have encountered.
I purchased a 4.3" diagonal TV (designed for car use) and successfully connected it to the Pi (via RCA cable) and a USB cable for power (it can run off 5v). My goal is to embed that display into my waterproof Otterbox connected to a Cell-phone recharger USB battery. I will power the Pi also via another Cell-phone recharger USB battery.
The problem that I'm facing at this point is connecting all the cables and still fitting everything into the box.
For the RCA video connection, I need to take the cable from the mini-TV which has a female RCA and connect it to the Pi which also has a female RCA, so I need to have a male-male connector, like this one:
sold by Adafruit.com
But, that's going to stick out really far from the Pi, especially when I connect the connector on the end of the TV's cable to it. I might try to get a right-angle RCA connector like this:
I haven't found a good source for this connector in Canada; if you can find one, please let me know.
But, really I should get a male-male right angle RCA connector which does not seem to exist. If anyone can find a male-male version of the right angle connector, please let me know.
The other solution is to just remove the female connector from the video screen and replace it with a male connector that I can plug into the Pi. If there is a short male RCA connector that I can attach to the video cable, that would be awesome! Let me know if you know of any.
The situation is even worse with the USB connections. I connect the GPS breakout board to the Pi using this USB to TTL Serial cable:
Holy cow! Look at the length of the USB plug on that sucker! It almost doubles the length of the Pi when plugged in!
I'm using the same cable to connect the Battery to the video. But the battery has the USB output power on the side so it more than doubles the width of the battery. Ack!
There's a swivel adapter:
But even the swively part of that sticks out about 1" beyond the edge of the Pi.
Crazy thing is I have a USB Wifi adaptor that is tiny in comparison and it does 802.11b/g presumably had an antenna inside, and only sticks out about 2mm:
Wow, that's nice and small.
So if anyone has any ideas on <how to build/where to buy> a "short-profile" USB connector, please let me know.
Once, I get these pieces resolved, I can finish the physical build.
The next step after that will be to start pulling data off the sensors and displaying them on the screen (first, while I walk to work, then on the boat).
Stefan Kremer