The Youritronics electronics lab has a new look: 2 new benches and shelves all of them hand-built. When space is an issue you really have to make the most out of it. One thing is sure, I need more Ikea plastic boxes. On the first bench I do most of the electronics stuff while on the second one I do all the other stuff like assembling - disassembling or breaking stuff. Also on the second bench you can see my DIY reflow oven.

youritronics electronics bench 2

BlueRover

The past few months I’ve been working on the project for the Digilent Design Contest so I was quite busy. Together with my colleague Dragos I worked allot on this project but the results were great, our project the BlueRover won the 1st place so I say it was well worth it. First of all Digilent provided most of the parts needed for the project like :

  • 1 x Cerebot 32MX4 dev board
  • 4 x dc motors
  • 4 x HB5 motor drivers
  • wheels, metal pieces to put everything together

Besides these we also used:

  • 1 x LiPo 2S battery
  • 1 x 5V dc to dc converter
  • 1 x 6v dc to dc converter
  • 1 x BTM222 bluetooth module
  • 1 x MQ6 LPG gas sensor
  • 1 x MQ7 CO sensor
  • 1 x TMP275 digital temperature sensor
  • 1 x MMA7455 digital 3 axis accelerometer

The idea of a remote controlled rover excites almost every electronics student and when we heard about the Digilent contest we realized that we have the possibility to make such a project real. We decided to build our own remote controlled rover but it had to be different from what we’ve seen before. We came up with the idea that we could control the rover by using accelerometer data and that we could use a second accelerometer placed on the rover to sense the driving surface.

I handled the Rover with the sensors and my colleague took care of the control unit which is a Nokia E55 smartphone running a custom application in Python. The principle is simple the control unit sends acceleration data to the rover every 100ms thus controlling the movement of the rover. The rover reads data from the on-board sensors (CO, LPG, Temperature, Accelerometer, and Battery) and sends it to the control unit every 100ms. The control unit receives sensor data from the rover and reacts according to the rover accelerometer by vibrating on each bump sensed by the accelerometer. At the same time the control unit displays sensor data on screen.

I’m not going to go into details about the source code or the specs of all the boards we used in this project but you can find those in our report which I’m linking at the end of this article. I would like to add that Digilent RO did a great job in organizing this contest, it was a really great experience to be there and I’m sure we’ll be there next year too.

You can watch photos from the contest here: http://picasaweb.google.com/digilen.ro

Now I’ll leave you with a demo of our project captured right at the contest presentation:

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Downloads:

This article will be followed up by one dedicated to the BTM180 and BTM222 bluetooth modules from Rayson. Due to the lack of documentation on this module it was really difficult to get them working and I would like to share my experience for those who are facing the same issues.

If you make a lot of prototyping, especially with SMD components like myself you need to make for each design its own pcb. With SMD’s the one layer design usually isn’t feasible and since the component pins doesn’t run trough the board  the double layer approach results in many vias, even for a simple schematic you can have 50 of them.

Off course everybody can order from the factory trough hole plated pcb and they are off the hook, that is the professional solution and for the end product I do the same. But that costs more, there is a lead time and if there is some error on the board or on the schematic, you need redesign and order another one.

I personally use home-made double layer pcb’s for my prototypes, with photo method and some design constraints like track width, spacing,  clearance, the results are quite good.

Double layer pcb home made vias

Yes, that’s nice but it has a lot of vias, and can be painstaking  to make the connections for each via by running  through a thin wire, soldering one end then soldering the other end, cutting down the excess, because for each via you have to handle the wire, the soldering iron, the cutter resulting a great “overhead”. I admit this was my solution and took hours to make each via separately, until somebody showed be a clever trick, but that’s enough talking, here are the pictures:

You need some thin copper wire:

You need some thin copper wire:

First anchor one end of the wire by soldering to one side:

First anchor one end of the wire by soldering to one side:

Run through the vias(like sewing) the wire:

Run through the vias(like sewing) the wire: Run through the vias(like sewing) the wire:

Solder each end:

Solder each end: Solder each end:

Start cutting as close as possible(on each side):

Start cutting as close as possible(on each side):

The result:

The result

Nice, round bumps :)

Nice, round bumps :)

And after soldering the TQFP package:

And after soldering the TQFP package:

As you can see, the vias underneath the TQFP doesn’t cause any problem, although more attentions is needed when soldering. Fast and simple, hope you get the spirit and start tinkering.

December 31st, 2009

2009 Youritronics highlights

This is the last post for 2009 and I promise there will be much more in 2010. In 2009 we had some interesting projects developed here at youritronics.com here is some of the highlights:

20 Band Audio Spectrum Analyzer

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The analyzer is currently at v.2.0 and it has allot more features then it originally had. Kits are still being produced and the shop has a new look.

Clever Digital I/O handling in C

A nice tutorial written by Laci which caught the attention of the hobbyists.

Seven segment display explained

Another really good tutorial written by Laci an youritronics author, explaining the 7 segment display and how to use it with microcontrollers.

Matrix keyboard explained

The same good quality tutorial signed by Laci this time explaining the matrix keyboard and how it can be interfaced with a microcontroller.

matrix keyboard demo

RGM-3550LP GPS module connected with Asus Eee pc

The idea behind this project was born when a friend asked me too take a look at he’s broken GPS unit (MyGuide 3000) to see if I can fix anything. After figuring out that the processor is the faulty part I decided to use the gps module for a stand alone gps module that you can just connect to a netbook.

TMP275 digital sensor thermometer

The TMP275 is a 0.5°C accurate, Two-Wire, serial output temperature sensor. I got it as free sample from TI and I put together this project to experiment with the sensor.

The 3 part DIY speaker building tutorial written by youritronics author Andrei, the kind of project that gets the most out of everything using inexpensive materials:

subwoofer

As i said in part 1 of this project i wanted to build a 2.1 system with good sound using most of the components i already owned and keeping the costs as low as possible.  Since the satellite speakers are not going to be used below 100Hz you can fit almost any 6.5″ woofer in there and since the box is closed. You can also use speaker filling to match the Qtc of the satellites with the subwoofer’s low pass filter. However you need to focus on voicing. Crossover between woofer and tweeter is very important and many times i found it’s making a big difference in sound. If you open most mainstream commercial speakers you will see a only a capacitor and/or resistors or something like that.

Now the subwoofer, since i don’t have much information on the drivers i have, i had to do some measurements. I found a Qts of about 0.76, Fs – 46Hz and Vas – 36l. Yes, i guess it’s made in China. No matter, it will fit a 60l (internal) box very well. The box will be sealed because the woofers are not that good and i will place it in a corner this way i will gain up to 6db in output. The thing about rooms is that their dimensions equals the wavelength for low frequency and this leads to room modes and room gain. If you have a subwoofer you might have experienced that in the room there are certain places where the bass seems to disappear. Take one step away and the bass appears again. This is due to room modes. Going lower in frequency there will be no more waves in the room and the room starts to pressurise and you have a gain going 12db per octave.

This is a generic box. You can fit in there a couple of 10 inchers too. What you must look at is strong motors in the woofers. Big magnets, thick top plates, big diameter voice coils all this will help the woofer perform in a sealed box.

Now to the build itself, first i cut the material i need using a circular saw.

circular saw wood sub box

After all the wood boards are cut, i use glue the boards together. Use of clamps makes things easier. Bracing the box and making the joints as solid as it possible will lead to best results. Heavy is good in subwoofers! After the glue is dried i applied the carpet on the box, corners protection, handles and connectors.

carpeting1 carpeting2 carpeting3 carpeting4 amp

Once subwoofer construction was completed i focused on it’s amplifier. I had a car amplifier with it’s smps busted and i thought it’s just what i needed because it already has adjustable low pass filter. The corner frequency can be selected from 40Hz to about 200Hz. So i removed the defective smps and i installed a mains transformer rated 150VA which gave me +/- 35V dc after rectifier bridge. Also used 10’000uF caps for filtering. In most car amplifiers the case is used as a radiator so i had to put new radiators for the power transistors. All this and the amp board i put in a deceased Pioneer Cd player case.

Here’s the 2.1 speaker system:

2.1 speakers

Time to power the system. The satellite speakers are amplified by a JVC integrated amp and the subwoofer by it’s own amplifier with each channel to its woofer. Set the subwoofer low pass filter to about 100 – 120Hz. Sound was good however some tweaks were still needed in satellite crossover, it sounded bright. Waveguides rule! Here are frequency response graphs. Between two horizontal hard lines there is a 3db difference divided into 5 other thinner lines. The roll off after 10Khz is caused by my old mic.

fr1smooth – satellite speaker                           frwholesys – whole system

I compared the sound of this 2.1 system with a pair of Cerwin Vega CLS-12. On the high mid-range and highs my system has more detail. I think that tweeter with the waveguide is too good to be used with this system haha. Ofcourse the CLS goes deeper and with a couple dbs louder and the big difference is seen when you turn the volume up. The 8″ woofers from my sub can’t keep up with the 12 inchers from the CLS but they do have a fair amount of excursion as you can see from this small video:

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Here are the dimensions of the speaker cabinets and the crossover schematic with one modification the 6.8uF cap from the tweeter high pass filter must be changed with a 4.7uF cap.

schita final xover

This is it for now, I’m sure there will be more changes to the crossover and probably i will test other drivers for subwoofer as time goes by but for now i’m pleased with the result. I wanted a 2.1 system to use with my PC because the two CLS-12 speakers are too big to be placed near my desk.

Anyways if you have some woofers, drivers, tweeters, horns my advice to you is to get your tools and try and build a speaker for them and you might be surprised with their sound and you will have lots of fun in the process specially when you will blow your friends’ commercial setups.



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