3D Graph, meet 3D Printer

So awhile back I ran a stand on robotics and my PhD resarch at a Bristol University public engagement event Changing Perspectives.

One of the most visually assertive parts of my research in robotic movment have been the 3 dimensional plots I use to represent effort considerations in reaching motions. The idea is that the workspace of the robot makes up 2 axis on the graph, while the other axis represents the effort (a combination of graviational and muscular considerations). When planning movements to vertical targets, the robot can aim to keep it's trajectory in the lower parts of the graph, thus reducing effort during movement, as in casual human motion.

Some people find the concept of a 3D graph quite hard to grasp, which is fair enough, so I decided that a nice way to engage the public would be to make the graph tangible. Hence I had it 3D printed.

To make it more inutitive  I then created a contour 'heat' map of the simulation, which I projected onto the surface. This meant that points of high effort were highlighted with 'hot' colours, while low regions were coloured with colder shades of blue. Really this could of done with some projection mapping, but I didn't have much time.

Finally, I simulated the robot moving accross the surface in real-time to give the whole thing some motion and context. Unfortunately I was too busy chatting to the visitors to get a video of the projection on the graph, so here's the raw video:

Multiple LED pulsing via a 555 timer

UPDATE - The bug in the last schematic has been corrected. R2 had been incorrectly connected to Pin 7 and GND instead of Pin 7 and Pin 2.

I noticed awhile back that there were a few people in a few forums asking for simple ways to make LEDs pulse. During the summer I designed a circuit that pulsed a number of LEDs as part of a fancy dress costume. I was told that it looked great :-) Anyway, here is the circuit. It uses a single 555 timer in astable configuration to create a square wave. On the high part of the wave it triggers one LED, on the low part it triggers the other LED. The big capacitors cause the fading by charging and discharging the square wave into something more analog than digital.

Note: This is Version 3 of this circuit. A lot of people sent me messages saying that they were having a few issues building the circuit. There were a few problems with the previous schematics. The first was that the line connecting pin 2 and 6 could of been misinterpreted as also connecting to pin 7. I've now colour coded that line and put junction indicators (black dots) to show when two wires should be connected together. I recently realised that while making this correction I accidently connected R2 to GND instead of Pin 2. This is now fixed.
The other error was that the dotted line part had the led connected to ground after the capacitor instead of before it. As necro_nemisis pointed out this meant that LED1 was on a direct path from 5V to ground. I dread to think of all the dead leds that drawing mistake was responsible for!

Sorry it takes me so long to do corrections...

The effect is quite nice and you can add more capacitors in series to get several LEDs to light up in a chain. Here's a video where I had 4 sets of LEDs running from one 555 timer (shown at the end).



In addition, here's a photograph of how I wire up the 555 timer IC on some stripboard (with the strips running vertically from top to bottom). The only cut tracks are under the 555 chip. Note there is a red cable hidden from view behind the left capacitor which connects the other red cables together. I would only use this picture as a reference for the IC wiring, rather than the caps, as it is hard to see which track the capacitors are connected to.