Glow-in-the-Dark sketch wall and LED pens

I've finally realised one of my childhood dreams; I'm now the proud owner of a glow-in-the-dark wall - just don't tell the landlord!

I've had some glow-in-the-dark paint knocking around for quite a while and was inspired to do something with it when I saw this post on hackaday.com - "Record player display sans POV". I thought "the kids" would have a lot of fun using LED flashlights to write on something that was phosphorescent.

To start with I just coated some stiff card with the phosphorescent paint and hacked together a simple UV-LED flashlight. The flashlight design was taken from this Instructable - "Make A Mini LED Light". I found it while trying to find ways to make my own battery holders for a more standard flashlight, but this idea was so simple and small that I decided to go with it instead. All I did was to substitute a UV LED in place of a standard one.

After making the prototype I showed it off to "'er indoors" (this may not mean much to you if you didn't grow up watching "Minder" in the U.K.). Her response was a little unexpected - "Hmmm.... why don't we paint the wall with glow-in-the-dark paint? That way loads of kids can play at once!". So that's what we did :) We isolated a good amount of wall with painters tape, we just wanted it to be slightly taller than the kids. Then we put on 2 coats of white primer, 3 coats of the glow-in-the-dark paint and a couple of layers of varnish (so the kids didn't immediately scrape off the latex based glow paint). After removing the painters tape, I was pleasantly surprised to see that the wall didn't look much different.



Unfortunately, my night time camera skills leave a lot to be desired (i.e. they're crap), so I don't have many pictures of the kids playing with the wall. I can say that they were very excited and played with it for days & were very keen to get all their friends to play too whenever they came over. At one point we had a complete sea-scape covering the whole canvas with storm clouds, jellyfish, 'normal' fish and deep sea monsters. In the picture below I'm holding one of our home made light-sabers next to the wall in an attempt to allow the camera to focus (see this filthwizardry post for more lightsaber fun- "balloon and torch lightsabers").

I think one of the favourite activities, however, was with an old SLR camera flash. Get the kids up against the wall and blind them with the flash. If they recover (ok, you could just tell them to close their eyes) they'll get to see themselves glowing in silhouette form on the wall .

Hmm... ok, maybe it was one of my favourite activities as well.

After a couple of days playing, I ended up buying some LED keychain flashlights (like these from Amazon) as I quickly ran out of parts.

Here's a few in-production pictures of the ones I made:

I made 4 to begin with. All you need is a pushbutton, a UV LED, a coin cell battery and holder (and a soldering iron + solder for connecting it all up).

Connect the positive lead of the LED to the positive battery holder connector, cut off the rest of the lead so it doesn't get in the way, then attach the pushbutton to the negative battery holder connection and the negative LED lead. That's it!

Here's the first one working (nice purple glow). Some hot glue made for good protection and electrical tape wrapped around the base of the LED helped to focus the beam.

You should probably use a resistor to protect the LED... The datasheet for my LED stated that it required 3.2V to operate and the coin cell is only rated at 3V so I decided to leave the resistor out.

Important: Bright lights/UV lights can damage your eyesight. Do not shine the lights into anyone's eyes and make sure any kids playing with these are supervised and told to shine the light only at the wall. Extra care should be used when using UV light - the human eye can not detect it (i.e. you can't see it) which makes it easier to overexpose your retina as you don't have the same pain response as with intense light in the visible spectrum.

If you're nervous about this then the standard keychain lights work pretty well. The homemade UV ones just give a longer lasting glow.

Duplo Traffic Lights

We've been playing with LEGO and DUPLO quite a lot at home recently (Lin's been doing some great work on expanding our LEGO possibilities - see these posts over on filthwizardry: "Lego and hole punching cards", "Festive card punching with more LEGO", "LEGO and DUPLO" and "LEGO car and DUPLO truck cardboard printables").

I thought it'd be really nice to be able to add some traffic lights (like these ones I made a while back) to the creative fun. Lin suggested I house some in a DUPLO block, so I set to work trying to figure out how to do it.



Ingredients: 3 LEDs (red, yellow, green), 3 resistors (I used 330 ohm), ATtiny13, 8 pin DIP socket, perf board, magnet wire (thin), switch, stranded wire (black and red), coin cell battery, DUPLO blocks (the 8 knobble variety, 1 standard and 2 thin).

Tools: soldering iron, dremel, hot glue gun, various dremel attachments and drill bits (depending on your LEDs and switch).

The three holes/cylinders on the underside of a standard DUPLO block are perfect for traffic light mimicry. I ended up using 3 blocks, one large and two thin. The large block houses the electronics and the switch, one thin piece has 3 holes drilled in it for the LEDs and the last piece is used on the back as a battery cover.

Here's a couple of pictures showing the carved out bricks. You have to leave some of the 'tubing' in the large brick in order for the other brick to still connect normally. I used a dremel to cut off the 4 middle bobbles from the thinner piece - leaving a hollow center, between the two pieces, for the electronics.



I haven't taken a picture of the remaining thin block, I hollowed that out in the same manner as the larger block, to make room for the coin cell battery. Again leaving enough of the innards so it'd still fit tightly on the back of the main block.

I drilled 3 holes in the front piece (the thin black one above) directly in the center of the three tubes; the holes need to be just the right size for the LEDs to fit snuggly (I messed this up with my first prototype). I also drilled a small hole in the center of the big block for the power wires to feed through later on. This way you can have all the electronics hidden in the main block and have the battery accessible on the back.

The main board is just a small bit of perf-board with the 8-pin DIP socket soldered on. I'm using the same code as last time, so the LEDs and resistors are attached to pins 5, 6 and 7 (PB0, PB1 and PB2 respectively). I used magnet wire to attach the LEDs as it's flexible and takes up very little room. I tried just soldering the LEDs directly onto the perf-board but that made it difficult to get a good fit later on. If you give this a go, remember to sand the insulation off the ends of the magnet wire before soldering.



Add a switch:


Then place it all inside the main block (feeding the power wires out of the hole in the back).



Then glue the LEDs into the holes of the front piece and close it all up. I'm probably going to have to glue it shut in the future to keep out fiddling fingers.



I didn't have a coin cell holder, so I scavenged some metal tabs from the innards of a happy meal toy and soldered these onto the ends of the power leads. Then I taped them tightly onto the coin-cell. Clip on the battery cover (3rd block) and it's all done. This would all be a bit cleaner if there was a coin cell holder attached to the back in some way (I'll give that a go next time).

Here's the lights in operation (with my first attempt on the right which has directly soldered LEDs and an ugly switch):



The kids really do seem to like them! The original lights have had to be repaired a few times from er... 'overly keen' play. Well, that and Ffion ripping them apart.

Next ideas are to make them easier to include with normal duplo play by attaching blocks to the top and bottom (may require some cutting and gluing). Another good addition would be to have lights on both sides of the block to control traffic in both directions (so when one side is green the other is red). If only I had more black duplo...

64-bit Windows 7 and the AVR ISP USB programmer

Just a very quick note about this.

I upgraded my laptop to 64-bit Windows 7 a week or so ago and have just gotten round to setting it up for AVR programming. I thought for a while that I'd never get my USB programmer to work (AVRStudio couldn't auto detect my AVR ISP even after installing/reinstalling). After a little bit of searching I found this thread on avrfreaks.net. I followed the directions, allowed windows to discover the correct drivers at the end of the process and, badabing-badaboom, everything now works fine (other than the fact that I installed a 32 bit Eclipse that isn't happy...).

LED Tester Mark II

Ok, so the last one I made had a serious flaw... it'd burn out any LED that couldn't take 3V... Oops! I recently bought a new soldering iron (variable temp, xytronics from allelectronics.com) and wanted to play with it, so I thought it was time to replace the LED burner with an LED tester.

Basic ingredients: wire, some resistors, an 8 pin DIP socket, a pushbutton and some perfboard. I treated myself to an automatic wire stripper the other day ($8 from Fry's), it's great! I've been using it quite a lot. No need for it in this project really, but I like to show off my toys.

Here's the basic wiring and soldering for the resistors and socket (this is what I messed up in the first iteration):

At midnight I ended up with the following "finished" product (I should have learned by now not to start late at night...):

The problem was that I'd completely wired the push button wrong. In the above wiring, the power lines are connected to the positive and negative rails on the DIP socket, which meant the LEDs lit up as soon as they came in contact with the DIP. On pushing the switch the LEDs would turn off because the positive and negative leads from the battery holder were shorted... bah!

A few days later, I came back and repaired it (button connects and disconnects +ve terminal, -ve terminal is wired directly):

A view from the top.

Single LED test. You can see the multi-LED test picture at the top of this post.



The soldering iron is much better than the Weller I'd bought (it was a bottom of the line weller min you). It heats up fast and the tip is noticeably better quality. The power cord, however, is very thick and reduced the maneuverability of the iron.

Flashing Bat Eyes

Very simple project. You just need a 555 timer a couple of resistors, a capacitor, a couple of LEDs and a talented wife to provide a bat ;) I think she'll be adding a post on making the Halloween bats so I'll link to it once it's up.

I used the following online calculator to work out the values for R1, R2 and C1 for the standard astable 555 set up. I ended up with: R1 = 3K Ohm, R2 = 570 Ohm and C1 = 100uF (mainly because that was the combination of components that I had lying around and that gave an acceptable output wave). I didn't bother adding a switch to this one, I'm not sure why as it'd be very easy... here's the fully wired up project:

Did you notice the 9V battery clip onto an 2xAA holder? Weird eh? Useful though. I think I picked up the battery case at radioshack. You'll also have noticed that I decided to try a free-form (no perf-board) approach. It was a bit fiddly, but worked out ok. I still haven't found a combination of 3rd hand/clamp/foot/nose that works for me for these fiddly soldering projects...

Here's a couple of close-ups of the soldered 555 itself:

Most of the time I had the 555 held with a crocodile clip (on the 3rd hand). Unfortunately, I bought a really cheap 3rd hand from a market and the crocodile clips are not stable so everything kept moving around whilst I was trying to work on it... bah. At points I ended up jamming the chip into a corner of the 3rd hand base whilst pushing at it with the soldering iron. Not very elegant or skilled... any advice is greatly welcomed!

All that's left was to poke out some holes for the bats eyes and to mangle it all into the available space. I made the holes big enough for the dome of the LEDs to fit through but small enough to prevent the rest of the LED housing from pushing through.

And here it is outside our house (flashing on the opened door frame), waiting to welcome the trick-or-treaters :)

ATmega programming board

Recently I've been playing with some projects that required more IO pins than the ATtiny has to offer. I bought a few ATmega8's from ebay and have about 3 of them installed in various breadboards at the moment. All the wiring was getting very frustrating, so I decided to make another programming board to reduce the clutter and to make my life a bit easier.

The process was almost identical to that for the ATtiny header board. There are only two real differences: 1) this is a board designed to fit the ATmega8 AVR chip so it has a 28 pin DIP socket and 2) I used a bad purchase (wide 28 pin dip socket) as the female headers for wiring up to the breadboard projects.

The wiring is practically the same as the ATtiny board. If you've ever wired an ATmega to a breadboard (or to anything else) you'll easily be able to work this out. There's more room to maneuver with the larger 28 pin board as well, which was nice.

Here's the 'bad purchase':

I mistakenly bought a few of these wide 28 pin sockets (as part of another allelectronics purchase). These have been sitting in a drawer all but forgotten. I noticed them whilst retrieving the narrow 28-pin socket for this board and figured these would be useful as female header rows if I just chopped them in half. It turns out they fit really well & look pretty good too.