PICAXE in the Streets


Senior Member
I'd like to share some insights into my recently completed, very public, PICAXE project. I have been working with local public artists Phil and Dawn Gamblen to make a striking piece of street sculpture.

In daylight hours, you see three brightly coloured topsy-turvy standard lamps appearing to be speared into the pavement. At night the lamps become, well, lamps! Light from custom-made high-powered LED lights is projected downward through laser-cut holes onto the brick-paved town square (Actually, it's a triangular paved area but let's not spoil a good story!)

The sculptures themselves are made from heavy-gauge sheet steel, cut, rolled, folded and welded. The light apertures all conform to entrapment regulations. The tallest lamp structure stands nearly 5 metres high. Once sharp edges were removed, the lamps were hot-dip galvanised as single pieces before being painted in an aircraft hanger. The three lampshades are firmly secured to reinforced concrete foundations under the pavement and interconnected with electrical conduit.

Each lamp structure houses five 30W RGB LED lights aimed outwards and downwards from the centres. The display emits a maximum of 450 Watts of coloured light although software limits the maximum power, preventing overheating problems. A purpose-built 800W linear power supply runs from the mains.

The lights are driven by three interconnected PICAXE 28X2 boards that I designed. The 28X2s are interconnected via a short i2c bus, with one configured as a master and the others as i2c slaves. A small solar panel or cell from a solar garden lamp connects to the master PICAXE, allowing it to detect dusk and dawn for switching the display on and off. Each PICAXE drives three (for RGB) 10-bit PWM channels at about 975Hz. Each colour channel is driven by a P-Channel MOSFET configured as a constant current generator modulated by PWM. P-Channel FETs were chosen because, as a constant current source, they can limit damage should an earth-fault develop in the cabling or LEDs.

Identical software is loaded into all three PICAXE controllers. The slave 28X2s have a pull-down resistor wired, countering internal pull-ups in different pins to change their identity. The master PICAXE generates 10-bit random numbers for the intensity of the red, green and blue LEDs under the control of each controller board. The software in each PICAXE then controls the change between each set of colour intensities in a slow, seamless manner, making the colours slide or 'morph' between colour sets. The colour intensity is also controlled to compensate for the non-linear sensitivity of the human eye.

The artwork was installed in mid-November and the lights were switched on for the first time a few days later. The photo was taken on a quiet evening but does not do the colours justice - the result is quite mesmerising, even if I say so myself. The permanent display will feature in the summer 2015 "Light Up Leederville" carnival, this coming weekend.

(Photo by Philip Gamblen)


Well-known member
I have two interests right off the line:
  • How did the artists visualize the lighting effects, and how did they transmit those visualizations to you so you could program them?
  • How did you weatherize the electronics and protect from those noisy city industrial power lines?

Looks fantastic. I agree with you about the paltry visualization from that photo. Perhaps a short video would do the trick?


Senior Member
Thanks for you comments.

How did the artists visualize the lighting effects, and how did they transmit those visualizations to you so you could program them?
You have probably guessed that the artwork was commissioned by the local city council. As you can imagine, competition between artists and ideas if stiff, so many good ideas don't get off the drawing board.

The entire process for this project took about 18 months from concept to delivery, with activity varying from nil to 'very intense'. The concept drawing was done in "Sketch Up", which has quite amazing capabilities for visualisation in the hands of an experienced user. We tossed around a lot of ideas before Phil and Dawn put their proposal to the committee.

I work quite closely with the artists - this is the 6th commercial project we have produced together. We have also worked on quite a few proposals over the years that were not accepted at the time. Those ideas are saved, waiting for the right client. Phil gives me a fairly long leash to try out both hardware and software ideas - a few work the way we want, some don't. Some of those that don't work on one project might suit another. On a job like this one, I beat a trail back and forth between software development at home and the actual sculpture or a wooden mock-up until everyone is happy with the result.

How did you weatherize the electronics and protect from those noisy city industrial power lines?
Water can only enter each "lampshade" from the perforations near the pavement. Cover plates on the upper side of the lampshades have custom-made neoprene gaskets. I built the power supply, controller, light enclosures and cable connectors to IP66 standard to allow the sculptures to be cleaned with external water jets when required.

Protection from electrical interference is by good earthing, shielding, design and possibly some good luck. The circuit board design has been a winner for me over several projects. Care was taken to separate the logic and lighting supply paths and earthing, with 'star' distribution wiring from the logic-level voltage regulator. Each MOSFET is switching about 1 Amp at 975 Hz, so there is a fair bit of electrical noise being generated on-board.

Photographing the sculpture while operational at night is a challenge. The contrast between the intense colour from the LEDs and the ambient street lighting is too much for the camera (a top-end Canon). I think we'll have to Photoshop more than one image together to approach what the eye perceives. I'm sure that, over the coming months and years, there will be many photographers and videographers accepting the challenge. As an aside, there was a thunderstorm a couple of nights after the installation, before the lights were operational. A suggestion came in a day or two later that we should arrange for the artwork to be photographed next time there is a night-time thunderstorm. Easier said than done!
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Senior Member
How did the artists visualize the lighting effects, and how did they transmit those visualizations to you so you could program them?
To further answer Tex's question, I found one of the original SketchUp concept visualisations that the LED lights were based on. The keen-eyed of you may notice that the (paint) colours of the lamps were rearranged during the process!


Well-known member
Fantastic! I use Sketchup for everything I build. My project's only variables are my ability to "hit the marks" while building. With Sketchup life is so much easier.

The insight you leave here about your project are much appreciated, IWP.

PS. Now if I can just find me an artist ... :D