ICRS Design Hackathon - Stair in the DarkFollow project
Sherif Agbabiaka, Aleera Ewan
Stair in the Dark
The aim of our project is to determine a sustainable way to generate light in homes during periods of emergency, for example, power cuts. We decided to use piezo materials to do so, placing them on the stairs so that when people walk up and down the stairs, due to the piezo-electric effect, the lights along the staircase would turn on and guide the persons’ way. During periods of non-emergency, our project stores the generated electrical energy in rechargeable batteries. In periods of emergency, a switch can be closed that will cause the lights to be turned on. Applying oscillating pressure to the piezo material causes it to generate a current proportional to the pressure.
The piezo circuit:
On the left of this circuit is an array of piezo elements, these will be the parts that will be stood on by the user. It needs to be connected to a diode rectifier in order to make the AC current into DC allowing an LED to be powered.
This is the PCB design that we would use to create the circuit above
Preventing Overcharge of the Rechargeable Battery
We had two options to prevent overcharge in the rechargeable battery: to use a Zener diode, which would limit the voltage since it would ensure that the voltage remains constant, restricting the voltage between the rechargeable battery and the piezo material, therefore preventing overcharge while simultaneously preventing discharge of the battery to the piezo materials.
*see Zener diode
The diode is in this direction since the current is flowing from the piezo material (the external voltage supply) to the rechargeable battery, therefore preventing discharge. We then need to connect this section of the circuit to the lights, so that when the switch is closed, the rechargeable battery would allow the lights to turn on.
*see rechargeable battery LED
The alternative option was to use resistors to ensure that the maximum current per hour flowing through the circuit would not exceed the maximum current per hour that could flow through the battery.
*see rechargeable battery resistor
Since the current is negligible and it is the output voltage that is high (approximately 20V output when standing on the material), we decided that the Zener diode would be more effective.
CAD DESIGN (FITS UNDER STAIRS)
*see CAD design
These pads are designed to fit together so that multiple pads can be connected to fit any size of stair or platform. Ideally, the notches on each side will be electrically connected so that no additional wiring needs to be done, making it easy for anyone to piece them together.
Of course, we will need the piezo elements, but to turn into a pad, we would need a vessel for it, to create a sort of composite material. The material would have to be compressible but also provide protection for the brittle piezo crystals. This leads me to use a thick gel sac to maximise the pressure applied.
*see stair image
The stairs will have a normal base (probably wood), something solid for the piezo pads to be placed on. Over the pads will be a carpet or any other kind of floor finish the user may want.
In conclusion, this design is a sustainable way to reduce the risk of injury in emergency situations such as power cuts. The piezo effect means that the lights on the staircase will appear to work in a similar way to motion sensors, whilst being more energy-efficient. To improve this design, we would focus on making the process of turning on the lights more automated: we would measure the voltage across the mains power supply. When the mains voltage falls to zero volts (for example during a power cut or other emergency), we would use an inverter as well as a BJT transistor as a switch, instead of the toggle. We could also improve the user-friendliness of the project by incorporating an app that would show the length of time left for the lights, based on the remaining charge in the battery.