Simple Clock

Just clock that shows time, accurately.

Component base is very simple:

• Arduino NANO v3 chinese replica (on Atmega-168 chip)
• 7 segment 4 digit LED indicator with common anode, FYQ-5641BD-21 (red LEDs)
• 8 resistors that limiting current on LED segments, 330 Ohms, 0.25 watts
• RTC Module GEEGROW with DS1307 chip (very basic, only RTC chip, quartz resonator, button battery, no additional memory chip)
• 5x7 cm single side prototyping board
• usb phone charger as power supply
• 2 push buttons
• 1 on/off switch
• Gainta G521G enclosure (92x66.5x28мм)
• 5m power cord

Optionally you may need:

• Capasitor with well capacity if your charger has small capasitor on output
• Fuse, to protect your device
• DC/DC transformer if you have power supply that gives more than 5 volts or less than 4.5 volts (this will give additional surge protection if your power supply dies, this can happen after 3-5 years of uninterrupted work)

Additional Notes:

My RTC module is not very accurate due to bad quartz chrystal calibration, looks like it is not exactly 32768 Hz and clock runs faster than it should be, giving about 5-8 seconds runaway per day. So i have to implement time correction in software (temperature changes during day/month/year is not very big - about 10 degrees Celsius, so we can use software compensation without thermal compensation).

This project split into 2 branches:

• default that contains generic clock without any additional elements
• photoresistor that contains additional hardware - photocell bridge - and software algorithm that compensates ambient light sensed by photocell basing on LED display charachteristics.

Stable tags for branches:

v1.5 - default v1.4 - photoresistor