Shopping list 2

Last night, I ordered a few more items from some of eBay's abundant "Free postage, but two month wait time" sellers in China.

As noted in a previous post, I discovered that pretty much all of my my power supplies, are unregulated, and deliver about 40-50% over-voltage when under no, or light loading.  The same will be true if I ever get around to using a solar panel to charge my 12V batteries.  So I've decided to build a simple regulator box, that can take anything up to 20V (my biggest mains power supply units are 12V - putting out around 18V, and a 12V solar panel can also get up to around 18-20V under ideal conditions.), and put out a regulated 9 or 12V, which can then in turn be safely put through either the Arduino Uno or MB102 PSU on-board regulators, to provide 5 or 3.3V to my circuitry.

I've found a 'buck' converter based on an adjustable output LM2596 regulator, for just $1.25, that takes anything from 4.5 up to 40V input, has a fully adjustable output ranging from 1.5 to 37V (so appears to require an overhead of 3V), and can handle up to 3A of current drawn through it - but I'll hopefully never need anything like that amount.  This will be the core of my regulator box.

I found some 3-30V 3-digit LED voltmeters, for $1.20 each, and I am going to wire one of those on each side of my regulator, to monitor the input and output voltages.

I will put a 2.1mm jack on the input side (salvaged from one of many old bits of hardware in my 'junk' box at work), to take power from the mains DC units, but at the moment, I'm not sure what to do for the connections on the output side.  Obviously, I want the regulated voltage to feed the Uno, but as the Uno has a limited potential for current, it would be nice to also be able to tap directly off the regulated supply for higher powered devices, such as fans and motors.  So maybe I'll have 2 output options - a simple 2.1mm plug that can connect to the Uno and MB102 for low power control circuits, and then the option to tap directly into the regulated voltage at higher amperage if required.  Just not sure what kind of connection to use for this - perhaps some form of PCB mounted pin connector that I can then connect to the breadboard using DuPont cables..?  It would be nice to mount all this in a little jiffy project box, and then mount it onto a board with the Uno, LCD, and breadboard all permanently mounted as a mini workbench.

The next item I've purchased is a Real Time Clock (RTC) module, based on the DS1302 chip.  I've read a few warnings saying they aren't the most accurate of devices, but to be honest - I don't need something that is accurate to less than a microsecond over 10 years... I just get fed up having to keep type in the seed time and date for any time-based projects while I am testing them.  So for $1.00, even if it loses a few seconds a day, it will do for my needs... maybe I can get some sort of wireless connection next time, that will allow me to reset the clock time from my PC or the internet once in a while.

My final purchase, was a bundle of header pin strips.  I got one set with my Uno clone, but have already used about half of them on my little breakout boards and for other testing, and that's without putting any on the Uno itself.  I've got a bundle of ten 40 pin strips - should keep me going for a while.

So, now I just need to sit back and see how long they take to arrive.  I placed all 4 orders last night 9th July, and 3 of the 4 claim to have 'sent' the items already, two with an ETA of 'before August 8th' (WOW - just ONE month!) and one (sadly, the regulator itself) not until September 1st.  I guess that means they have been packed and thrown into a 40ft shipping container on a dock somewhere, and when the container is full, it will be loaded onto the next cargo carrier coming our way...

The final item (RTC) has not yet been sent, though ironically, its ETA was the earliest at August 3rd!
I'll update this post as and when the items arrive.

11/07 - I got notified overnight that the RTC has now also been despatched, with an ETA of August 2nd.  Today, I also made one more purchase, this time of some 1x4 female header pin PCB connectors.  Thinking ahead to mounting all my gear on a little workbench, I want to utilise the extra bank of optional connection points for power and SDA/SCL, and build a custom semi-permanent I2C connection cable.  I could have ordered a pack of 10 of them from another Chinese supplier for $1, and waited till September, or pay $2 for the same pack of 10 and have them on Friday... I'm getting a little fed up with waiting for China's free "Economy International Post" option, so I paid the extra dollar and will be able to put up a post showing my upgrade at the weekend hopefully ;-)

25/07 - Ironically, the LM2596 regulator - the item with the latest ETA - arrived today, two days ahead of the start of the potential delivery period, and a full 5 weeks ahead of their final ETA date!