Chasing Illuminated Staircase
The RSAMD's production of Flight included a curving, illuminated staircase. Each step had a frosted perspective panel in the riser which would illuminate and each step was individually controllable from the lighting desk.
The set for Flight was an airport lounge, comprising an open waiting area flanked by curving walls. Above the waiting area was a catwalk platform, supposedly leading to the aircraft. A staircase following the curve of the stage left wall led between the stage level waiting area and the catwalk. Each step on the staircase had a frosted perspective panel in the riser which was to illuminate. The lighting for each step had to be individually controllable to allow for chases and other effects to be created.
Design and Resource Limitations
The lighting design for the production was substantial and as such consumed all available dimmer channels. The production budget would not allow for the cost of hiring additional dimmers, therefore solution to the staircase had to be found that did not rely on dimmers. Additionally, at the end of the performance, all the set pieces moved off stage except the staircase. This meant that any cabling required would have to be able to be disconnected and removed or hidden before the scene change to leave the staircase standing alone onstage.
The solution to the staircase challenge was to use low voltage lamps to light each riser, and have each lamp turned on and off via a relay that was driven by an 0-10volt analogue control signal from the lighting desk.
This solution had these advantages:
- The staircase could be controlled from the lighting desk
- No additional dimmers were required
- The lamps could be battery powered, therefore minimal cabling was required:
- Mains cable for the Demultiplexer
- Control cable from the lighting desk
This disadvantage was that the lighting for each step could only snap on to full and off - fading was note possible. However, this was the agreed compromise to create the effect with the budget and resources available.
The Control Circuit
A circuit had to be designed to allow the 0-10volt analogue control signal to power the relays that would turn each step's lamps on and off. The signal from the demultiplexer did not provide enough current to drive the relay coil, nor enough to drive a transistor. Therefore, the signal from the multiplexer had to be stepped up in two stages. First it was passed through a 4011 NAND gate, then through a transistor & finally passed over the coil of the relay.
Passing the signal from the demultiplexer through the 4011 logic gate gave the advantage of a clean on/off signal going to the transistor (the channels used for the stairs on the lighting desk were also set to non-dim). A 0 to +10 volt demultiplexer was used, as oppopsed to the more common 0 to -10 volt, which allowed the demultiplexer signal to drive the 4011 inputs. 4011 chips were used because they were available in house. The output from the logic gate had enough current to drive the base of the transistor. However, as the input signal passed through the NAND gate it was inverted - i.e. the output from the NAND was high when the input was low and vice versa. Because of this a PNP transistor was used. The PNP transistor activates when the base voltage drops. The output from the transistor had enough current to drive the coil of the relay.
9 volt power was supplied from a normal domestic mains transformer, which could output upto 450mA. 12 power for the transistors and lamps was provided from a car emergency jump-starter. The jump-starter was placed inside the staircase and was trickle charged during rehearsals and between performances. This meant that only a single 13A extension cable and a single control cable were run to the staircase.
The staircase had 15 steps, so the circuit above was replicated to include 15 resistor/transistor/relay sets. As each 4011 chip contains 4 logic gates, only 4 chips were needed. The circuit was soldered together on strip board. Individual wires were soldered to the board for each of the 15 inputs. These were group into two groups of 6 and one group of 3. Each group was soldered to an 8pin din connector to connect to the demultiplexer. The 0v lines from the demultiplexer were also wired into the din and connected to the common 0v on the board.
Ring connectors were used to connected each of the relay switches to the 12 supply (the jumpstarter). The other side of the switchs had short wires attached that connected to pieces of terminal strip. This allowed the control circuit to be easily disconnected from the lamps. 2 12v lamps were mounted behind each perspex panel on the staircase. Each pair was wired in parallel. The wires for each pair of lights connected to the terminal strip on the circuit and via ring connectors to the -ve terminal of the 12v supply.