Lets look inside Nomad

Above is the circuit I built for the purpose of powering the LED PCB. At the heart of the circuit is a LM317 adjustable, three terminal regulator.

Initially setup without a 20 ohm resistor in line with the voltage out. This amendment to the circuit was needed to control the current feeding in to the PCB. Which caused the first setup to overheat and fail. In plain English, the microchip on the PCB melted, well near enough!

For the correct voltage to output from the circuit, the values of resistor’s R1 and R2 had to be determined. As my maths is terrible, I cheated by using an online calculator to figure out the necassery values. Which turn out to be 120 x 150 = 2.81 Volts. This was under the 3v given to the PCB by the 2 AA batteries that originally powered it. But given batteries are a constantly depleating power source, I did not think feeding a constant 3 volts in to the PCB would be healthy in the long term. Which is why I choose 2.8v.

I have to say that when it came to making this circuit, I found it quite a challange. I’ve always had a love for taking things apart, rebuilding them. But that has always been easy to me. It’s like working on a three dimensional jigsaw, where the pieces are components, which all slot together in a specific way. But making a circuit from nothing, this was something else, especially as I did not fully understand circuit diagrams and symbols. Luckily consulting several people online via IRC, proved the most useful thing I could have ever done. It is thanks to those individuals i was able to understand what i was doing and actually turn a rough diagram in to something that functioned.

With it completed, I connected a universal PSU outting 3v 1.5mah and tested the regulator. Nothing, the thing had zero output. except from when i hooked the voltmeter to the V in and ground. So something was wrong. I had nothing coming from the V out and Adjuster. While to this day I’m not sure how it happened. R2 somehow became perminently open, perhaps it was a faulty component, who knows. But for the cost of a few pence, i wasn’t really bothered. In addition to this, i had the feeling that my brief fight with a stubborn soldering iron, which refused to get properly warm. Had resulted in the regulator being damaged. In the end, I bought full set of replacement components. Using my dad’s older 70’s soldering gun, yes a gun with a trigger. I was able to fit the replacement parts in minutes. Honestly i dont know how i’ve managed so long without having this tool, compared the standard wand iron i have. The trigger iron, applies heat when you need it.

With the new components in place, i tested the circuit and discovered huzaar 2.8volts!!  When i saw the reading pop up on the multimeter I was relieved. As i was sure the reason for the fault had been something i had wired wrong. But no, the circuit layout as it turned out was good.

With the circuit tested, I set about putting all the parts together within the case. The end result was a rather full looking box of wires and parts and myself looking ever more worried something would surely come loose.

Switching from the universal PSU to the internal mini ITX power supply did not strike me as anything that would set off a red flag. Having taken in to account the 12v and 5v feeds, I had already worked out that i would steal power from a redundant HDD molex connector. When the machine powered up, it was on the kitchen side. Everything worked! Leaving the system on while I went for my camera up stairs. I thought five minutes turned on would tell if everything was working. I couldn’t have be more correct. On my return i noticed one of the LED’s was nolonger working. Flicking the switch, it came back in to life, while two others had died. Placing my hand over the microchip on the LED PCB to check the heat, the hot glue covering the chip stuck to my hands. It wasn’t warm, it was cooking! Powering down for 10 minutes and then back on, revealed the PCB was indeed cooked beyond repair.

It was at this point i realised something i had overlooked, the current! the universal PSU had a maximum output of 9v 1.5mah. But what rating was the Uniross adaptor i was now using to power the entire system through the ATX power connector? A lot more then 1.5mah.

Advertisements


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s