OUTERNET – Quick Power Guide

Since the Raspberry Pi foundation posted about their Outernet installation, and thanks to the Raspberry pi guys sending me a spare tuner card, I have been busy setting up my own system.

I really like everything about the Outernet project, the goal, the hardware and the team behind it.

I have been frequenting the forums, and the Outernet team have been superb in troubleshooting my snags. I also want to help other users, so, in response to a power related question on the forum, I’m going to describe my hardware set-up, so hopefully others can follow.

There are plenty of DIY guides from Outenet on how to purchase and assemble the hardware. The information below is specific to me, and isn’t the best or only way to do it!

First, check the input rating on your hardware, both voltage V and current A.

I have three items requiring power:

Pi 5V @ ~700mA (mA = milliamp – one milliamp is 1/1000 of an amp, so 700mA is also 0.7A)

Geniatech HD Star Tuner. Supplied with 9V wall brick (but I didn’t get one so I don’t know its current (A) requirement.)

Netgear ADSL router. I’m using this to create my WIFI hotspot. 12V @1A as stated on the data sticker on the rear.

So, I had three separate voltages to supply, which would require additional hardware, and as I’m planing to run off batteries, this would be less efficient. Voltage conversion has an overhead of wasted energy.

The HD Star tuner generates the 18V DC required to power the LNB, so it must have some DC to DC conversion built in.

Could it be powered from 12V? I trawled the internet for an input specification, but didn’t find anything. I followed the PCB tracks from the input jack to see if I could identify the immediate components, and that was, well, challenging.

In the end I decided to just try it at 12V. No blue smoke, and it still works.

Great. Now I only need 12V and 5V.

Luckily I was powering my Netgear router from a 12V DC 2000mA (2A) PSU, so I spliced an additional DC jack into the 12V cable for the tuner.
TEST SETUPAt this point I plugged up everything to get it working, with the Pi still powered from a 5V USB phone charger.

To convert 12V DC to 5V DC for the Pi I used a DC to DC buck converter. These clever little circuits are cheaply found on ebay, and can take a range of input voltages, and provide an output that is set via a small potentiometer.

Sacrificing a spare USB cable, I soldered the red wire from the micro USB connector to the +V output terminal, and the black to the 0V.  I then spliced another pair of wires into my 12V PSU, and “trimmed” the output to just over 5V.

I made some assumptions that are still to be verified:- the Pi will be drawing 700mA, the Netgear wont draw anything like 1000mA (1A) and the tuner will draw approximately 500mA*, so the total current draw should be under the 2000mA rated PSU output.

*Previous test set-ups had the tuner powered from a bench DC power supply. It was well below 500mA.

Below is a schematic:


The 12V DC cables were simply cut, spliced with solder, and covered in heat shrink.

Everything was boxed up in a peli case. The connection to the LNB passes through the case on a F type bulkhead adaptor, the power goes through a gland, and the wifi antenna is connected to an ebay extender cable. This makes the whole unit rain proof. My intention is to attached the peli case to the pole.

I should also mention that there is an in-line DC plug and socket between the mains adaptor and the splice in the cable. This allows me to plug into any 12V DC source available. I have powered this from SLA batteries and a cigarette lighter socket in a car.setup

With the aid of a cheap satellite finder, I can be on the air in less than 5 minutes, providing I have line of sight to 13E.  One warning, a car cigarette lighter socket can be higher than 12V, and that voltage would be passed directly to the router and the tuner.

This image shows my completed terminal.  The cable going off the bottom is for the 12V DC input.

Right now I am scaling some solar panels and batteries to run it off grid completely.

If you have any questions, look me up on the Outernet forum, user John Space, leave a comment here, or tweet me @johnchinner


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