inglewoodpete
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)
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)