Archive for the 'howto' Category

dc booster PCB

Published by matthew venn on September 26, 2011 in howto, news and projects. 0 Comments

This aim of this project is to build a small, adjustable DC/DC converter with an input from 1v -> 5v and an output of 5v->12v at up to 1.2A. With a 3v to 9v conversion at 1A it is 85% efficient. Photos taken during the design process are here.

IMAG0456

After much searching I found and successfully tested the LM2623 (datasheet here). This great little converter chip does just what I need. The only problem is that it’s tiny! So this project is the one where I finally conquer my SMT fears!

I prototyped the board first with through hole and then with SMT components. The schematic and board are available here.

I used pretty much default component values from the datasheet. The only thing I did different was to add a trimmer for adjusting the output voltage.

dcdc schematic

All components are specified to 2A. The last numbers in the list below are all farnell part numbers. It works out at £4 each plus vat for 10 kits.

You can buy a professionally manufactured circuit board from me here:


dcdc board
SMT tips

SMT is a different technique to through hole, and requires some different tools. The most important things are a magnifying lens of some kind, liquid flux (I use a pen with good results) and solder braid to remove excess solder. Fine tweezers and a fine tipped soldering iron are also very handy.

Before soldering a component, apply flux onto the pads. Then place the component and check alignment. Apply a bit of solder to the tip of your iron and touch it to the pad while holding the component still with the tweezers. The flux helps the solder flow into the gap between the pad and the component’s pin. Now the component is attached, check the alignment and then move on to the other leg(s). This time apply the solder to the join like soldering through hole. Finally, go back and touch up the first pin you soldered. Check everything thoroughly with the lens after soldering. Having to go back to fix things can mean removing other components first!

For the tiny chip, solder it in place as above, and carefully check alignment! Then apply solder to all the pins and don’t worry about bridging. Use some of the fine braid to remove the excess and you should see a beautiful joint after!

Construction

Before starting it is worth scraping the white silkscreen off L1’s pads – this is a mistake I made when making a custom device in Eagle.

Place the components in this order:  C3, R3, RF2, C1, IC1 (then test), L1, D1 (stripe on the right), RF1, C2.

After placing IC1, check these connections with a multimeter:

  • pins 1 & 5 -> ground
  • 2, 6 & 7 -> + out
  • 3 -> bottom pad of C3
  • 4 -> left hand pad of RF1
  • 8 -> D1 (+ out side)

Testing

Check the input resistance is large (above 1M). Then set your PSU to 3v and if you have current limiting set this low, 100mA is fine. Apply the current and you should see about 8.5v on the output. Use a screwdriver to adjust the trimmer and set your desired voltage.

If you get 0v or the supply voltage out then you probably have a bad connection somewhere. I’ve found bad joints on the big cap (C1), and the diode. I’ve also missed a pin a few times on the IC, but if you check the connections as I’ve listed above then this shouldn’t be an issue.

If you get a large negative voltage it will be because C1 isn’t connected properly.

Notes

At very low start up voltages (<1.5v) the board will look like a short circuit because the DC/DC controller shorts the input to charge the inductor. It needs about 2A to start at these low voltages, and then the current will drop to normal.

A beginner SMT artist will take about 30 minutes to build and test – as long as there are no mistakes!

Improvements

  1. Bigger pads for trimmer and C2
  2. Remove silkscreen over L1 pads (actually tdocu layer)
  3. Indication of positive side of D1

virtual graffiti instructable / howto

Published by matthew venn on December 18, 2009 in howto, news and projects. 0 Comments

I’ve finished the first version of the virtual graffiti system, which is now fully published (including all code) on the instructables website.

We ran a demo at the blue hut youth club on Thursday where it was very well received!
demo at blue hut youth club

linux ubuntu 8.10 + processing + wiimote + wrj4P5 = virtual graffiti!

Published by matthew venn on November 20, 2009 in howto, news and projects. 2 Comments

Inspired by the various wiimote graffiti offerings, but finding no source or instructions (did I not look hard enough?) I decided to do it myself. Here is the first step: getting processing working with the wiimote infrared camera to detect an infrared LED.

After installing processing, I found some instructions on the forum, but I still had some problems. Here is what I had to do:

  1. install processing
  2. install bluez libraries: sudo apt-get install bluez-utils libbluetooth-dev
  3. create ./processing/libraries/Loc and ./processing/libraries/wrj4P5
  4. download bluecove-2.1.0.jar and bluecove-gpl-2.1.0.jar and put into ./processing/libraries/wrj4P5/library/
  5. download wiiremoteJ v1.6, and put the .jar into ./processing/libraries/wrj4P5/library/
  6. download wrj4P5.jar (I used alpha-11) and put into ./processing/libraries/wrj4P5/library/
  7. download wrj4P5.zip and unzip into ./processing/libraries/wrj4P5/lll/
  8. download Loc.jar (I used beta-5) and put into ./processing/libraries/Loc/library/
  9. download Loc.zip and unzip into ./processing/libraries/Loc/lll/

Then I used code inspired from Classiclll to get the buttons and sensor bar working. This code just draws a circle where the 1st infra red source is found by the wiimote:

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import lll.wrj4P5.*;
import lll.Loc.*;
Wrj4P5 wii;

void setup() {
size(300,300,P2D);
wii=new Wrj4P5(this);
wii.connect();
}

void draw() {
background( 0 );
fill( 255 );

Loc p=wii.rimokon.irLights[0];
if (p.x&gt;-1) {
ellipse( (1 - p.x)*width, (1.-p.y)*height, 10, 10);
}

}

Thanks to the bluecove team, the bluez team, processing crew, Classiclll and all open source massive!

raw vegan chocolate recipe

Published by matthew venn on December 26, 2008 in howto. 0 Comments

ingredients

  • about equal amounts of cacao butter to cacao powder. Use small amounts of coconut butter instead of the cacao butter if you want a softer chocolate.
  • agave nectar to taste. I used 10 tbsp for 3 cups of cacao butter and 3 cups of cacao powder.
  • raw coconut butter
  • flavourings (vanilla pod, orange and ginger, chilli, cinnamon and cardamom)

method

  • Gently melt the cacao butter/coconut butter using a glass bowl over warm water (careful about the heat if you want the chocolate to remain raw)
  • stir in the cacao powder, agave nectar and any flavourings
  • after the mixture is smooth, pour into a suitable mould (ice cube trays or tupperware is fine) and transfer to the freezer for 15 minutes
  • turn out onto a plate and let the chocolate come back up to room temperature for maximum flavour and texture appreciation!

full colour concrete moodlamp

Published by matthew venn on December 22, 2008 in howto. 0 Comments

A weddding present I made Charlie and Rachel a few years back. I hadn’t got round to putting up some instructions till now. Check the instructable here.