January 7th, 2016
The Light Doorbell uses a flash of light, rather than the sound of a bell, to indicate someone is at the door . Great for the deaf and those annoyed by the sound of someone ringing your doorbell over and over again.
Step 1: Materials + Tools
- (x1) Disposable camera. I used a Kodak FunSaver from Walgreens.
- (x1) Keyfob Single Button RF Remote Control - 315MHz from adafruit
- (x1) Simple RF M4 Receiver - 315MHz Momentary Type from adafruit
- (x1) 5VDC relay from Radio Shack
- (x1) Clear 4.3" x 1.6" x 3.3" project box from Amazon
- (x1) 1.5V regulator. I used LT1587CT-1.5 from Digi-Key
- (x1) NPN transistor. I used TIP120 from adafruit
- (x1) USB Micro-B Breakout Board from adafruit
- (x1) 220 Ohm resistor
- (x1) 5 x 7cm PCB from Amazon
- (x1) Micro USB cable
- (x1) USB wall charger
- (x1) 22 gauge wire
- (x1) 60/40 solder
- (x1) Soldering iron
- (x1) Electric Drill + drill bits
- (x1) Wire strippers
- (x1) #0 Screwdriver
- (x1) Needle nose pliers (optional)
- (x1) PanaVise (optional)
- (x1) Sharpie (optional)
- (x1) Self-healing cutting mat (optional)
Step 2: Prep Disposable Camera
WARNING: The internal capacitor is a high voltage and might retain some voltage after discharging. Before removing the enclosure, discharge the capacitor by triggering the flash. With the flash triggered, begin desconstructing the camera. Remove any stickers. Use the screwdriver to press the tabs in and pry the case open. Remove the battery. Once the circuit is exposed, identify the flash trigger and flash charge switches. As a precaution, use an insulated screwdriver to short the flash trigger switch. Continue and extract the circuit.
With the circuit extracted, solder a wire to each flash trigger contact. Also solder a wire to each battery contact. Next solder down the flash charge switch so the flash is always ready to discharge. To do this, first remove the metal button. Bend a short uninsulted wire across the exposed contacts. Solder the wire in place.
Step 3: Assemble the Circuit
Use the below picture for reference when arranging the parts on the PCB. Use the below schematic to know how to connect the parts. Solder it to the PCB accordingly.
When the RF Remote Control button is depressed a 315MHz signal is sent to the Receiver. Pin D2 of the Receiver is momentarily set HIGH. This momentarily closes the gate of the NPN transistor, completing the path of the relay. A relay is used because the flash trigger voltage is too high for the transistor. With the relay active, the flash trigger is closed and the flash triggers. Because the flash charge is always closed the camera is always ready to flash or getting ready to flash. The camera normally runs on a simple AA battery. To replicate the power supply we've replaced the battery with a 1.5V voltage regulator conected to the 5V USB power supply.
Step 4: Project Box It
Place the circuit inside the project box. Identify where the micro USB cable needs to go and mark with a Sharpie. Use the appropriatly sized drill bit for your micro USB cable and begin drilling. Connect your micro USB cable. Secure the lid using the #0 screwdriver.
Step 5: Enjoy
Place somewhere within range of the RF remote control and in the area with the most traffic, such as a living room. Plug it in and wait patiently for a friend to come over and ring your new doorbell!