I’ve been trying to make electronic fireflies for ages now, and most of my previous attempts involved RGB LEDs, and one of them per ATtiny13 with code to flash a random colour now and again. This was always going to be a pretty expensive method, but after seeing http://www.instructables.com/id/Jar-of-Fireflies/ I realised it would be a much better idea to have one ATtiny13 control /many/ LEDs.

I wanted the first one to be in a jar, but in future I plan to have much longer wires so that I get one controller PCB and 12 fireflies extending off to cover a corner of a room, or part of a ceiling, etc. I could even add an LDR so it can detect dark, possibly by using pin 1 (so the chips couldn’t easily be reprogrammed).

The circuit schematic is kind of odd: I took a normal 2×3 matrix, where PB0 and PB1 control the two columns (as they can do PWM, so all LEDs can be PWM controlled), and added another LED for each position but in reverse. Since all the ouputs can tri-state (where effectively they act as though they were not connected), I can light up any LED I want individually.

While I could easily extend this to a full charlieplexing scheme, that would mean losing the hardware PWM for every LED. I could easily add another two LEDs between PB0 and PB1, but it’s really not worth the added complexity - 12 is plenty!

Each LED is an 0603 green LED soldered to two very thin wires, which run to a home made PCB at the top of the jar. The battery holder is a standard kind of cell holder from Rapid, and on the other side of the PCB is the ATtiny13 (soldered to the solder-side directly) and two 180 ohm resistors. The entire thing is through-the-hole because I don’t have any surface mounted ATtiny13s lying around and did have loads of 180 ohm through the hole resistors.

The code is fairly simple: in an infinite loop it chooses one LED at random, lights it up following a rough sine wave (actually modeled on a real firefly flash!) and then might repeat it once or twice, then waits a random amount of time before doing the whole thing again.

Each time the thing is turned on, a value is read from 0×00 in the internal EEPROM memory and used as the seed for the PRNG, then incremented and stored - giving 255 different patterns, more than enough that you can’t see any repetition!

By far the most difficult part of this was soldering all the tiny LEDs - if it wasn’t for that, this would be a particularly easy project to pull off. Using normal through-the-hole LEDs is an option, or even LED holders which would solder to the PCB and an LED just slots in. Surface mount ones are small enough to be less noticable and look better when lit up, though.

Eagle schematic and PCB file, C source code and compiled hex file available at: http://randomskk.net/projects/fireflies_in_jar all files are released under CC BY-SA-NC license

I guess my new project has officially started! The PCBs I ordered from Golden Phoenix arrived today, a day short of two weeks from when I placed the order.

They’ve turned out really nicely, and I especially like the black soldermask. I plan to reflow solder the components on these using the grill in the oven - I don’t see why it shouldn’t work, but it may be difficult getting the right temperature. Who knows? I’ve got solder paste at the ready, at any rate.

I know I got them months and months ago, but I’ve only just had time to actually do anything besides work. While I do have a big project coming up (but not really at the point where I can write about it), I did finally make the PCB for the nixie power supply I designed a while back.

While I did realise I’d forgotten to put in a 56k resistor when I designed the circuit, I was able to add this in with a through-the-hole resistor I had lying around that was just the right size.

I powered up the circuit with a 9V battery and held my breath as the voltage reading on the multimeter jumped to 246! A quick turn of the pot on the back and the voltage hit 170V, ideal for the nixies.

I connected one up and lo and behold, it lit up! The glow really is ethereal - cameras cannot capture this, you have to see it in person. That didn’t stop me from trying, though!

The next step is to make a PCB to control all 12 nixies (probably with three of the power supply modules) and maybe link it into an RTC (though that is a bit boring - I might try doing something else, like GPS position?).

Schematic - Board (the board isn’t great, with some pretty fine tracks that run pretty close to each other, but it does have the 56k resistor I forgot in my version) (both files under CC-BY-SA-NC).

The twelve nixie tubes (and corresponding driver ICs) I ordered two weeks ago arrived today from http://tubes-store.com in Russia. They were beautifully packaged in two layers of foam and a cardboard box from some kind of kid’s milk in Russia. All the tubes are intact and in great condition considering they were made in mid 1980! The outer envelope even had my name written in Cyrillic as well as Latin, which is a neat touch. At any rate, all I need to do now is figure out how to generate 170V DC and I can power these things up! At some point I plan to make a clock with date/time. (how innovative, I know!)

It does have one problem out of the box, though - you can’t see it at night! A few small coin cell batteries and an LED soon fixed that problem, though:

This is my first prototype robot. A friend and I got together and he taped stuff to cardboard while I connected wires up and then we wrote a basic program and the prototype drove!

This version literally just drives forward until the ultrasonic sensor detects an obstacle, then it turns and drives forwards again. We can also rotate the servo the IR sensor is on and read the IR sensor, though we haven’t yet determined what voltages represent what voltages (it’s non-linear, typically).

The drive motors are the two servos I modified for continuous rotation, with an Arduino+Protoshield to control it.

This prototype has since been disassembled and work started on the new version, with a vacuum formed plastic chassis and normal geared motors harvested from an old toy. That one probably won’t get finished for a few months though, so I thought I’d post the cardboard prototype now.

This device analyses the music it picks up via the electret microphone, then flashes the LEDs in time to the music. It’s encased in the box SparkFun sent me the microphones in, since the box was just begging to be used as a case for something! I’m sure that was intentionally designed.

Getting a bit more technical:

The microphone picks up the noise and sends this to the LM386 amp, which amplifies it about 200x before it’s read by the ATtiny13’s ADC at 8-bit resolution. The ATtiny13 then keeps a running average of the noise level, and flashes the LEDs if the current volume exceeds the average by a scalar amount.

As a result, the LEDs flash on when the music hits a peak, and are off otherwise - no matter what volume.
The brightness of the LEDs is also somewhat correlated to the loudness of the peak, since a louder peak will generally keep the LEDs on for longer.

Check out the video of it in action:

Download the schematic, PCB layout, code:
https://randomskk.net/projects/lightstrip/ (all files released under Creative Commons BY-SA-NC 3.0).

I ordered some cheapo servos from ServoShop UK and had a play, they work fine.

However, to use them as easy-to-drive motors for wheels and stuff, you need to modify them to have unlimited rotation (they normally only have 180 degrees). This means they can no longer go to an exact position, but can be driven in different directions and their speed controlled, all through timed pulses - so much easier than wiring a motor, gearbox, H bridge and then controlling all that! (and cheaper, too).

Society of Robots has a load of great tutorials, and one of them details modifying servos to get continuous rotation. I followed the tutorial through for the HS-311 servos I had, and it works nicely.

I also photographed each step of the way to make a mini-guide on modifying this specific servo, hopefully this will help out someone with these (fairly common) servos.

Click the picture to go to step one, then step through each photo in Flickr (you can see the thumbnail for the next photo under the Set title):

It took a little change in the code to get it working with two matrices, but now it rocks!

Check out the video of it in action:

At the same time I got my new brush/scourer, I also got four 16-tray storage containers which were some £2/ea and looked ideal for holding all my parts, which had grown out of hand in the previous containers.

I quickly loaded them up and just got around to printing out some labels on cardstock and sorting them!

So I created a PCB for the Space Experiment mockup.

It’s functionally identical to the breadboarded version but is its own PCB, looks a lot better and has some text on it.

It actually took three tries to get it right. The first time, it all worked nicely and I etched it perfectly, only to realise I’d messed up the design!

I’m making the PCB as a shield for an Arduino, so it plugs into the top. I had the layout fine and was initially assuming I’d have the copper on the bottom (since the LEDs have to be on top), but later decided I wanted the copper on top. I quickly did a change layer to top for everything, without realising that I’d left the text mirrored! What printed, if made properly, should have resulted in mirrored text on top. Instead I made it so the text was readable - which means the copper had to go on the bottom for it to connect to the Arduino!

The next revision fixed this but was overetched and would have taken a whole load of fixing up, which is a pity.

Finally, I had it all perfect! All the text is really readable, I have a right angle socket for the LCD connector, and it all worked first time. Lovely!

I did have one new trick in the process this time:

This awesome plastic scourer thing has a nice, easy to use handle and really really tough plastic bristles, which are absolutely ideal for PCBs. Not only can I clean them at the start (and get the copper really nicely scratched up too), but it also strips the toner off like no one’s business. It’s taken about twenty minutes out of the process, especially when the transfer didn’t work and I have to take the toner off.

This was also the first PCB made with my new laser printer, which absolutely rocks - for PCBs, I print at 1200dpi, extra toner, high contrast, onto transparency, from the manual feed tray. I’ve set it up so I can just select the “Samsung_ML2510_PCB” printer on the list and all those options are used, so it’s just a case of hitting print and it does it. All the PCBs transferred really, really well with it! I can definitely recommend the Samsung ML-2510 mono laser for making PCBs at home.

So, I’m part of a team entering the UK Space Experiment Competition, and basically our proposal won out and is now one of six final proposals around the country! This is great stuff but we wanted to put on a display at a stand at a fair someplace, and for this we need something tangible!

The actual proposal calls for a piece of light detecting kit that runs some £1500 and we certainly can’t afford that, so instead I’m using a £0.50 light dependant resistor: pretty crude but works great!

What’s happening is the LEDs are being lit up, the Arduino reads the light level coming off the LDR and shows it on the LCD. When you put your hand or a piece of paper over the LEDs, the light reflects down onto the LDR, increasing the light level! In space, the bits of dust act as the paper and you can detect a whole lot less light.

The next step is vacuum forming a little case for the thing!

That turned out to be soldering 40 of them together and sticking them to my wall!

They actually light up my room fairly well:

For now, they are being run directly from a 3V mains power supply. However, once a few parts arrive I’m going to make a little PCB for them which will:

• respond to sound (with an electret microphone), flashing them in time to music
• be directly controllable through a pot on the case
• be controllable from a computer via USB
• be programmable to slowly fade themselves in in the morning, to simulate the sun rising and help me wake up

The 3.3V regulator and electret microphones are on order, and I’ll get getting the amp and some nice pots soon too! I’ll post when I get that working out.

I recently ordered 100 blue LEDs from eBay for a measly £1 (plus p&p of something like £3). To my surprise, they are both bright and all functioning!

However, I hadn’t really thought through what to do with them.

This was when I found a link to the charlieplexing instructable again, and decided to whip it together on a piece of protoboard. This turned out to be an absolute nightmare of wiring things up, hidden shorts, melting wire, all that fun stuff. In the end, I got most of the LEDs working fine, and a few are a bit screwed up. They can each be individually controlled using just five pins on the little ATtiny13 in the middle there, and it even has five input buttons (one per pin)!

This is a pretty neat use of tiny amounts of IO pins.

Unfortunately the back of the thing looks like this:

and I never quite got the courage to get the last few working.

I plan to instead make a PCB for them! Of course, the wiring there will no doubt be equally nightmaric, but at least the manufacturing should be easy.

I then got some requests from IRC and got to work: