Codebug - Flashing LED tree made with conductive paint

Last year I made some conductive paint using this Instructable.  For me 50:25 by weight, paint to graphite powder works great. Make sure to stir in slowly otherwise the graphite powder will fly.
With this mix the paint is easy to apply yet has good conductivity.
It worked great and I used it at a Raspberry Jam to make flashing LED eyes for Halloween.

Since then the paint has been abandoned until my eldest daughter mentioned she was making circuits in school yesterday and I said I'd try to make them flashing LED Christmas Tree pictures.
This got a thumbs up from my daughters so the pressure was on.

Using Inkscape I drew a simple Christmas Tree with a place to put 7 LEDs.
Nice and simple and easy to print on A4 card.  I made the baubles the shape of a physical LED so you can see which way to place the LEDs on the sheet. All the negative (ground, cathode) sides in the middle making it easier to connect all to GND later.

PNG Version.

Links to PDF and SVG 

With the drawing done I added the LEDs.  6 to the green tips and a yellow one in the star.  I had 2mm LEDs to hand so that's what I used.  For the real thing I plan to use 5mm as the effect should be better.

I found pre-bending the LED leads at right angles so they are pointing down when in places made it easier to  get the LED to stand up at the front.  I also made small holes using a pin to push the LED leads through.  It's hard to push LEDs through 300gsm card as the leads don't have a point.

Once this was done I turned over the card.  Left the ground side for each LED pointing down and turned the positive side (anode) out at right angles pointing to the edge.  Once done I used a small piece of tape to keep the LEDs in place.
Tip.  Push the leads down to they push against the card. It's means the leads lie flat making them easier to hold on with just paint.

Back of the card

As I mentioned the conductive paint had spent the last year drying so was a bit sticky meaning the paint job is less than smooth.  I have since revived the paint with a little bit of water so for the kids it should be much easier to paint.

The bar down the middle is the ground tied to all the LEDs.  The other lines are for the positive side of each LED.
If you want all wires to be at the bottom then you may have to adjust the SVG in Inkscape to only print one Tree per A4 landscape card.

To test I thought I'd use a Codebug I got in the Kickstarter and hardly used it since. They are no on sale at CPC Farnell
With the help of Twitter people (I didn't declare the legs as outputs at the top of my code) I put together the following program. Link to CodeBug site for project

CodeBug code

Once all this was done the LEDs flashed. Yeah!.

For this project I wired up the LEDs so the top and bottom on one side are paired with the middle one on the other side and vice versa and the star LED on a leg of it's own.
This only uses three  (3) legs on the CodeBug,s o the 4th one (3) in the code is redundant.  I just left it in there in case I can figure out a more exciting way to use 4 outputs to flash 7 LEDs.

Very Short video of the final tree.

Next I want to wire up to a Raspberry Pi to enable interactive input and independent control of all the LEDs and maybe play a Christmas tune as well.

Sidenote; Some might be asking where the current limiting resistor is.  It's the paint.  The conductive paint has a higher resistance than wire and so it is acting like the current limiting resistor.

Robot Club - fourth session completed

Link to Preparing post details in the parts in the kits.: http://winkleink.blogspot.co.uk/2014/11/preparing-for-2015-after-school.html

Link to First session; http://winkleink.blogspot.co.uk/2015/01/robot-club-first-session-completed.html

Note; I did not post for the second session. There is a short summary in the Third Session post.
Link to Third session: http://winkleink.blogspot.co.uk/2015/01/robot-club-third-session-completed.html

This week we nearly had a full house.
Only 1 child missing due to illness.

The 4 who attended the previous week remember a lot of their work and code so were getting stuck into getting their robots to go around a corner.

I had a bit more fun getting drivers on enough school PCs to permit the Arduino Nano to be seen. It needs custom USB/Serial drivers that are not included by default.

The teacher who is ICT coordinator came in to see the session in full swing with robots spinning, or moving along the floor. With coding going on and due to plus and minus lines on the batteries being shorted a nice little display of black smoke and the lovely smell of burnt plastic.
No real harm done just a jumper wires plastic sleeving was melted.
I congratulated the child on making smoke as it's something we all do when we work with electronics.  They were kind of shocked.
It was great that the teacher had the same attitude so no harm done and no concern about burning down the school.
I tested their robot kit and Arduino. Nothing damaged, amazingly so did a little bit of rewiring and handed them back their robot to get working on again.

On of the kids who was in the previous session had a problem where their robot was pulling to the left.  These are small cheap kits so the motors aren't tuned and the wheels are small and have grip meaning they catch on the carpet.  Meaning they cannot reliably go straight.
We tried to fix it by turning the wheels in or our to change the resistance but no go so introduced that child to analogWrite.
A value of 235 seemed to make it all work perfectly. They had a nice straight running robot.

Once again the kids were not that eager to leave as they were perfecting their code and making it better.

At the end one of the girls who was being collected wanted to show her mother what she had done so she gave a great demonstration of her robot.  Holding down reset to stop it moving.
Set it up and let it go. She then explained the code she had made as well as giving details on some of the other parts we will be using.

Next week we will be using an input device. A small line following sensor. I will mark the edge of the room area with white paper providing a contrast with the blue flooring. The idea will be to detect the paper and make the robot turn.
This will be the first time the kids do inputs and will also require the introduction of the 'if' statement.

Looking forward to another productive session next Monday.

Raspberry Pi + GPIO + Scratch + Remote Control Car

At the beginning of 2013 I started a Code Club at my local primary school and the kids love making and playing the games.  Due to the way the club is set up in the school there is expected to be a few classes after the official Code Club sessions are completed so I've been trying to come up with some ideas of things I could bring in to the class to show the kids that Scratch can do more than make a cat move around the screen.

Then on my regular trawl of the web I found this fantastic code http://cymplecy.wordpress.com/2012/08/26/scratch-controlling-the-gpio-on-a-raspberrypi/ for controlling the GPIO pins on the Raspberry Pi using Scratch.

With an old cheap remote control car in a drawer I had the makings of a fun project for me that (hopefully) will be of interest to the kids.

 Having read that the Raspberry Pi GPIO pins are not protected, so one silly mistake on my part could cause the death of my Raspberry Pi I dusted off my old electronics knowledge and put together a small transistor based driver circuit for the 4 pins used.

one circuit per pin

I originally wired this up on a protoboard and it worked, except for when it failed. Did I mention the remote control car was cheap. Well, the aerial was just a bit of wire and with all the other wires I added to the circuit there was regular interference that caused the remote to activate the wrong signal making it unreliable. Knowing the circuit was good the logical thing to do was to put the circuit on a proper board. Rather than going all the way to etching my own circuit board I made it up on a stripboard

again, 1 circuit per pin. white blobs under resistors are cuts in the tracks

After a false start (details of things I almost did wrong) I got the 4 circuits soldered up and tested.  Worked first time.

Not the prettiest soldering but after doing near no soldering for over 20 years I was happy with the result.

Now I the circuit soldered up and it worked. With a bit of coding in Scratch I could program the remote control car for a sequence of actions like
Forward 2 second
Left 0.5 seconds.
Reverse Right 2 seconds

As you'd expect from a simple remote control car the was no way to give very accurate instruction. The motor was either on or off, no variable speed or feedback.  Even with these limitations it felt great when I clicked on the code in Scratch and car actually did what I expected it to do.

the vehicle of my success!!!

And finally he is a short video of the car in action.

This is why I love the Raspberry Pi and the fun of hacking.  With a little bit of effort you can have a lot of fun. Now I have a remote control car that I can control with drag and drop commands in Scratch on a £30 computer.