Sunday, June 10, 2012

Portable repair workshop

I sometimes found myself in those situations where I wish I'd have at least ONE SIMPLE FLATHEAD SCREWDRIVER... And it didn't happen just once. So to be prepared for every common situation, I threw in a box what I think is essential to have when not at home.

Here's "the toolbox". I'll try to find something fancier, I don't like that one.
It includes:
-A portable soldering iron (lasts for about 20 minutes with a full tank, bought it for less than 10 bucks)
-A multimeter (low profile, cannot measure amps, but good enough to test continuity and voltage)
-Foldable pliers (I've got to find something lighter, that makes half of the weight of the entire toolbox)
-A small flashlight
-Bits and screwdriver (+ a small Philips for smaller screws)
-Cutter blade
-Metal saw blade
-A small roll of duct tape (actually, an old adhesive tape roll, with a few turns of duct tape)
-A lighter (not in the picture)
-A small bit of heatshrink tubing
-A nail (inside the heatshrink tubing)
-Coil wire + normal pieces of wire (inside the tubing aswell)
-Small pieces of sandpaper
-CA glue
-A hot glue stick (meltable with the lighter)
-Tin for the iron
-A list with all the tools and a resistor color code reminder.
The only thing missing is the lighter/
 I hope that with those tools, I'll be prepared for most cases of electronics breaking down. On the downside, I'd have to remove the iron and the lighter if I wanted to take it on a plane...

Friday, June 8, 2012

Everybody loves Nixie tubes.

I came across those lovely tubes last month...
IN-12A Nixie tubes... You can still see a "CCCP" logo. Gotta love old Soviet surplus.

Those things are pretty cool: they're the ancestors of the modern 7-digit display, and they give a nice and warm light! People now build blocks out of those, I just wanted to see what they're like, and maybe use them for something else one day (who nows, maybe another watch?).
So I bought four IN-12A off eBay, and built a small power supply for them.
I just wanted to light them up, nothing using a complex microcontroller control...
The power supply. I uses 5V AC, and turns it into 180V.
Inside view. Nothing really complicated, just a backwards wired transformer, capacitor, along with a few other things.
I used a case from an old 220 to 110V transformer that burnt out. The plug you see there is wired with a 4K7 resistor to discharge the capacitor when not in use... You don't want to get a 180V shock from this...
The schematic... As I said, I wanted something quick and easy to build :)

I just love that sweet glow!
Along with that, I built a small "tester box" that plugs directly into the power supply, and has a socket to correctly test the tubes... It has a rotating switch to toggle between each digit and a potentiometer to regulate the current going through the Nixie. 
Nixie tube tester... The switch you can see on the left side of the box selects the different digits... Because it's a 5-pos, I had to use another switch to toggle between digit 1-5 and 6-0.

Thursday, June 7, 2012

DIY powerful, yet cheap mobile iPod speakers

When I first thought about this, I wanted something that would be cheap and fun to build. I came up with a LM386-based speaker, giving a good balance between weight and power. Using a shoebox as enclosure, the whole thing weighted under 500g, battery and speaker included, for less than 20€ ($25-28).
It was loud enough to use it indoors, but less effective outdoors. The sound quality wasn't perfect, but good enough to be "listenable". All of this was built last year...
First version... The case? A simple cardboard, wooden box, with lots of hot glue. The holes were "drilled" without any alignment...

Back of the "box"... A small perfboard holds the two LM386, half a watt each. Everything is powered by a 9V battery

In February, I thought about building something a stronger than cardboard, with a bit more power to give, while keeping it portable. 
First concern: what would I use as amplifier? I wanted to keep the circuit as simple as possible. Searching through Internet revealed the TDA2003 as the best alternative... It has 10W of power, and doesn't need a symmetrical power supply, thus making it eligible for portable applications. 
The schematic used. Source:

The schematic is pretty simple, It's nearly the same as the one you can find on the datasheet... I reproduced the circuit twice for stereo. 
As power supply, a simple 12V 3Ah SLA battery was used. The speakers came from a car radio.
In the first version, the iPod was plugged in the headphones jack, with an annoyingly long cable. For this one, I wanted something clean. I bought a cheap iPod type connector to line out+USB cable off eBay for 4 bucks, and cut the jack to solder it directly to the amp. I kept a 3.5mm jack as alternate input, to plug in other devices.
Here is the Heavy-duty, more recent version... Still a simple box. I used a safety switch from RadioShack, thought it would look cool :)

Back of the device. I know, I have to tidy my wires up. The battery is hiding the circuit. In the upper part, you can see the "dock" cable.
Details of the amp. Simple, but powerful circuit. I added two heatsinks, but they never get very hot.

As for the case, I didn't want anything fancy... Remember: Keep it Simple. That's why I stuck to a simple wooden box. I never tried at full power yet, but at half throttle, it's already loud enough to be heard quite a distance away. Normally, the battery lasts for at least 3hrs, at medium power, without charging. It also includes an external power plug, that way I can use it when the battery goes flat (as for the charging, I'm using an external charger... I have to figure out something more portable). Still not audiophile quality, but it's already pretty good, I can't hear any distortion. 

The dock also has a charging feature (By sending 5v in the USB power line, along with 2.5V in the D+ and D- to trick the iPod into thinking it's plugged into an official product), but for the sake of autonomy, I added a switch to turn it off when not needed. I still have to fix a problem with the 5V regulator, it gets VERY hot, even with a heatsink, which is weird as the 7805 is rated at 1A, and the iPod Classic charges at 500 mA.

The only drawback I can think about is the weight: 3.5kgs! 7 times more than the first version... I had to lose a bit of portability for the benefit of power.

Total cost? 25€ (or $30)

Raspberry Pi rover?

I made a few years ago a small robot using a Lego Mindstorms plus my HP mini netbook... It was controlled with my local Wireless network, through another computer (using TeamViewer). The netbook was connected to the IR programming interface, linked to the RCX, and controlled the motors directly through Bricxcc. I could "see" through the Webcam embedded on the screen of the computer. We called it the "Kitchen Rover".

100% Lego. Well, except for the netbook.

 Pretty fun to play with, but the major drawback was that the whole thing was way too heavy, making it difficult to turn. Those little wheels were too small and fragile to withstand about 2.5 kgs of heavy Lego frame and computer. It was also subject to lags, the webcam stream plus TeamViewer used too much bandwidth.

Two days ago I ordered a Raspberry Pi. I was thinking about using it for making a small Media center (using XBMC), or a small Web Server. Then I tought about my small "rover". Why not use it as a controller, making the whole thing much lighter? I'm not sure yet if I'm going to use a Lego frame+motors like the first rover, I'll maybe build to something much sturdier, with more powerful motors (and using the GPIO pins instead of the lego RCX brick)...

For now, I can't do anything but wait. RS says "7 week lead time" before dispatching my order, so I'm going to stick to other projects until then...