Project Crystal (Part 1)

The journey for battery power ends up to be much more complex. The major concern is standby (light off) power consumption. I wished the circuit could remain standby for at least one week. With three 3100mAh 18650 battery cell at 3.7V each, the maximum allowed current draw works out as 3100 * 0.8 / 7 (days) / 24 (hrs) = 14.7mA (reference here, number of cells actually does not help, but LED light needs 12V). However, the Arduino Nano alone consumes 20mA when running. After removing the power LED, it still consumes about 17mA. The distance sensor, Sharp GP2Y0A21YK0F takes another whopping 20mA. With these two monsters, standby time is 3100 * 0.8 / 37mA = 67 Hours ~ 2.8 days (show stopper).

It seems I need to turn off distance sensor and put Arduino into sleep mode during standby. It is solved by adding a Passive Infrared (PIR) sensor which powers on GP2Y0A21YK0F only when human (or pet) walks near the light. Together with AVR sleep mode the current now reduces to 2mA standby. My standby time is 51 days 🙂

Here comes the schematic.

Notes:

1. Q1 controls power to the Sharp sensor. I tried to drive this sensor directly from an Arduino pin but failed. The sensor output is unstable. I believe GP2Y0A21YK0F  specified 20mA power draw is only average value. Its peak current is quite higher.
2. Q2 is reverse voltage protection (reference)
3. J_LIGHT is the main RGB LED light. J_LIGHT_BK is for backup.
4. R1/R2 is voltage divider for battery voltage measurement.
5. J_INDI connects to a Bi-color (Red/Green) LED light as indication.