Saturday, November 6, 2010

November 2010 – why so quiet?

Hello readers and visitors

November will be somewhat quieter than usual, I am relocating interstate which as you can imagine involves lots of boring, non-electronic work. So things will be a little quiet around here until the start of December. However your emails and questions will still be answered whenever possible. Follow me on twitter, or head over to my site tronixstuff.com - then subscribe (see the column to the right) to be notified when things are back to normal. 2011 will be much more interesting – I will have more work space, a house to modify, and even some products to offer. So stay tuned!

Wednesday, November 3, 2010

Kit Review – adafruit industries mintyboost v3

Hello readers

Today we are going introduce another useful kit from adafruit industries – their mintyboost kit. The purpose of this kit is to provide a powered USB socket suitable for charging a variety of devices, powered from a pair of AA cells. The mintyboost is quite a simple, yet clever design – the latest version is based around the Linear Technology LT1302 DC/DC step-up converter that we examined a few months ago - and can provide a full 5 volts DC at 500 milliamps, enough to charge the latest round of USB-chargable gadgets, including those iPhones that I keep hearing about. And unlike an iPhone, the mintyboost kit is licensed under a Creative Commons v2.5 attribution license.

But enough reading, time to make it. As always, instructions are provided online – are easy to follow and very clear. The kit will arrive in a nice reusable anti-static bag:

Which contains everything you need except for AA cells and a housing:

Where or how you contain your mintyboost is a subjective decision, and will probably vary wildly. The original design brief was to have it fit inside a tin that Altoidsconfectionary is sold in, however those are not available around my area. But I found a suitable replacement. The PCB is very small, and designed to fit snugly inside the aforementioned tin:

Very small – less than 38 x 20 mm in dimension. However with some care and caution, you can solder the components without using a vice or “helping hands”. Though if you have access to these, use them as it will make life a lot easier. Before we move on, please note that my 49.9k ohm resistors, ceramic capacitors and the inductor are a different size to those included with the kit. This is my second mintyboost, and to save money I bought the PCB only and used my own parts to make this one.

If size is an issue for you, it is a good idea to buy the entire kit, as you will have resistors that fit flush with the PCB, unlike mine :)

However, construction moved along smoothly, by following the instructions, double-checking my work and not rushing things. There is some clever designing going on here, I have never seen a resistor underneath an IC socket before!

But when PCB real estate is at a premium, you need think outside of the box. After this stage there was just the electrolytic capacitors and battery holder to install. One that has been done, you can insert some fresh AA cells and check the output voltage on the USB lines:

Looking good, however it could have been a bit higher if the AA cells were freshly charged. But the second USB voltage was spot on:

Success! It always feels good to make a kit and have it work the first time. The last soldering was to take care of fitting the USB socket, and then it was finished:

Now to take it for a test run. I have two USB-charging items to test it with, my HTC Desire:

The LED to the right of the htc logo indicates the power is in, and the battery indicator on the left of the clock indicates charging. Excellent. The phone battery is 1400 mAh – I most likely won’t get a full recharge from the two AA cells, but enough to get me through an extra night and half a day. The mintyboost is a perfect backup-charging solution to leave in your backpack or other daily case. And now for something from Apple, an iPod of about four years old (it still holds a charge, so I’m not falling for the “buy a new iPod every twelve months” mantra):

Again, perfect. Apple equipment can be quite finicky about the voltages being fed to them, and will not work if there is a slight difference to what the device expects to be fed. As you can see the team at adafruit have solved this problem nicely. There is also much discussion about various devices and so on in their support forums.

Now for the decision with regards to housing my mintyboost. The Altoids tins are not an option, and I’m not cannibalising my mathematical instruments storage tin. But I knew I kept this tin for a reason from last February:

Plenty of room for the PCB, the charging cable, emergency snack cash and even more AA cells if necessary. And where else could I have put the socket, but here:

:) I have named it the bunnyboost:

… who can safely live in the bottom of my backpack, ready to keep things powered at a moments’ notice. Excellent!

As you can see, the mintyboost is a simple, yet very practical kit. It would also make a great gift for someone as well, as USB-charging devices are becoming much more popular these days. If you are looking to buy a kit, those of you in the Australasian market can get one from Little Bird Electronics, or globally available from adafruit industries.

Once again, thank you for reading and I look forward to your comments and so on. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts, and if you have any questions – why not join our Google Group? It’s free and we’re all there to learn and help each other.

High resolution photos are available on flickr.

[Note - this kit was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

Monday, November 1, 2010

Kit review - nootropics design EZ-Expander Shield

Hello readers

Today we are going introduce an inexpensive yet useful kit for Arduino people out there - the nootropic design EZ-Expander shield. As the name would suggest, this is an Arduino shield kit that you can easily construct yourself. The purpose of the shield is to give you an extra 16 digital outputs using only three existing digital pins. This is done by using two 74HC595 shift registers - whose latch, clock and data lines are running off digital pins 8, 12 and 13 respectively. For more information about the 74HC595 and Arduino, read my tutorial here, or perhaps download the data sheet.

Before moving forward I would like to note that the kit hardware is licensed under Creative Commons by-sa v3.0, and the design files are available on the nootropic design website; the software (Arduino library) is licensed under the CC-GNU LGPL. Nice one.

However, there is a library written instead to make using the new outputs easier. More on that later... now let's build it and see how the EZ-Expander performs...

Packaing is simple and effective, like most good kits these days - less is more:

Everything you need and nothing you do not. The design and assembly instructions can be found by visiting the URL as noted on the label. The parts are simple and of good quality:

The PCB is great, a nice colour, solder-masked and silk-screened very well. And IC sockets - excellent. There has been some discussion lately on whether or not kit producers should include IC sockets, I for one appreciate it. However, what I did not appreciate was having to chop up the long header socket to make a six- and eight-pin socket, as such:

Why the producers did not include real 6 and 8 pin sockets is beyond me. I'm not a fan of chopping things up, but my opinion is subjective. However there are a few extra pin-widths for a margin of error, so life goes on. The instructions on the nootropic design website were well illustrated, however the design is that simple you can determine it from the PCB. First, in with the capacitors for power smoothing:

Then solder in those lovely IC sockets and the header sockets:

Then time for the shield pins themselves. As usual, the easiest way is to insert the pins into another socket, then drop the new shield on top and solder away:

Finally, insert the shift registers, and you're done:

The shield is designed to still allow access to the digital pins zero to seven, and the analogue pins. Here is a top-down view of the shield in use:

From a software perspective, download the library from here and install it into your arduino-00xx\libraries folder. Then it is simple to make use of the new outputs (20 to 35) on the shield, just include the library in your sketch as such:

#include <EZExpander.h>

then create an EZexpander object:

EZExpander expander = EZExpander();

with which you can control the outputs with. For example,

expander.digitalWrite(20, HIGH);

sets the new output pin number 20 high. You can also buffer the pin mode requests, and send the lot out at once. For example, if you wanted pins 21, 22 and 23 to be HIGH at once, you would execute the following:

expander.digitalWrite(21, HIGH, false);
expander.digitalWrite(22, HIGH, false);

expander.digitalWrite(23, HIGH, false);

expander.doShiftOut();

What happened is that you set the pin status up in advance, then sent all the commands out at once using the expander.doShiftOut(); function. The maximum amount of current you can source from each new output according to the designers is theoretically six milliamps, which is odd as the 74HC595 data sheet claims that 25 milliamps is possible. In the following demonstration I sourced 10 milliamps per LED, and everything was fine. Here is the sketch for your reference:

/* EZ-Expander shield demo
CC by-sa v3.0 tronixstuff.com/kitreviews */
#include <EZExpander.h> // you need the library  EZExpander expander = EZExpander(); // and to create an EZExpander object void setup()
{}
void loop()
{
for (int z=0; z<5; z++)
{
for (int i=20;i<=35;i++)
{
expander.digitalWrite(i, HIGH);
}
delay(1000);
for(int i=20;i<=35;i++)
{
expander.digitalWrite(i, LOW);
}
delay(1000);
}
for (int z=0; z<10; z++)
{
for (int i=20;i<=35;i++)
{
expander.digitalWrite(i, HIGH);
delay(250);
 }
delay(1000);
for(int i=20;i<=35;i++)
{
expander.digitalWrite(i, LOW);
delay(250);
}
delay(1000);
}
}

And the demonstration in action:

Overall, this is an inexpensive and simple way to gain more outputs on an Arduino Duemilanove/Uno or 100% compatible board. Also good for those who are looking for a kit for basic soldering practice that has a real use afterwards.

You can purchase the kit directly from Little Bird Electronics. As always, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts. Or join our Google Group.

High resolution images are available on flickr.

Otherwise, have fun, be good to each other – and make something! :)