Link to the Night Light Log: https://classes.engineering.wustl.edu/ese205/core/index.php?title=Night_Light_Log
It was a dark and stormy night... and it was so dark and stormy that you were in your house and couldn't see anything and tripped, fell and broke your arm. We wish to solve this epidemic of broken arms due to it being too dark by creating a light which automatically turns on in the dark, lighting up the darkness and making nighttime navigation possible!
- Ethan Shry
- Tony Sancho-Spore
We wish to construct a night light so that we are able to find our way around the house at night, even without turning the lights on, without having to manually flip a switch. We want to be able to put our night light into a standard light socket so that there is a way to store the night light easily without concern for losing it or stepping on it, and we also want there to be a way to turn the light on and off so as to not waste battery when not in use.
Most of this should be relatively straightforward, however soldering onto perfboard is notorious for being easy to miss connections or accidentally connect things that weren't supposed to be connected. It is advisable to carefully lay out the components on the board, and to double and triple check the schematic while assembling the circuit.
100K Ohm Resistor: $0.66
330 Ohm Resistor: $0.10
Photo Resistor (5mm GL5537): $1.78
9V Battery: $1.89
9V Battery Lead: $0.60
2N3904 NPN transistor: $0.21
2 5mm white LEDs: 2x $0.12
Slide Switch: $3.84
Total Cost: $9.08
Link to Digikey BoM: https://www.digikey.com/BOM/View/Index/7736660
Design And Solutions
For the housing, we designed a very simple box to house our night light. Due to time constraints we drilled holes in the box to fit the LEDs and photoresistor, but in the future we would make sure to take the time to design a box which fits the components better.
For the electronics, we simply soldered our components onto the perfboard as per the schematic. We did have an issue where we accidentally soldered a component on in an improper orientation, however with a little tinkering we were able to route the circuit appropriately so that our light lights up.
Our box works basically as intended. When the photoresistor loses visibility to light, the two LEDs turn on as expected, and the switch allows the user to turn the circuit off for long-term storage.
Overall our project went well, however we had a few issues. Our box design wasn't very robust- we ended up simply drilling holes in the box and taping it back together, where it would have been much more ideal if we had learned more about CAD and designed the box to have the proper cutouts and attachment points. Additionally, we dealt with our soldering issue by hacking some circuitry together, where it would have been more optimal to take the extra resources to redo the circuit (which we didn't do due to budget constraints).
It has come to our attention that some basement dwellers who live in low-light environments are unable to use our product because it never turns off. In the next iteration of the project, we will add a potentiometer to adjust the amount of light required to turn on/off the night light.
CAD Files can be found here (TODO put link here)