Twilight Mk2

The picture shows an updated version of Twilight driving a 3W LED inside a salt crystal. The new circuit:

• does away with the LEDs, using the controlled light itself as an indicator,
• ditches the variable resistor, using a long-press on the switch to indicate the light-level at which to switch on,
• stores this light-level in EEPROM to preserve it across power cycles
• uses an ATtiny85 for a smaller footprint

When switched on for the first time, the light is flashed quickly four times. When the environment reaches the desired level of twilight, the user presses the switch for two seconds to indicate this light level is to be stored. The light is then flashed slowly twice.

A circuit diagram and sketch (for Arduino 1.0) are shown below.

One-Wire Mains Switch

The schematic shows a one-wire controlled mains switch. One-wire is a simple protocol which is typically used for networks of temperature sensors. (The diagram is a simplified version of a circuit by Simon Atkins.)

Features of this circuit are:

• The diodes on the left provide surge protection, for those occasions when your network is hit by lightning.
• The DS2406 is active-low, the LED is entirely optional.
• The RC pair at the far right is called a snubber. It is used for inductive loads (e.g., electric motors) when the current is out of phase with the voltage. The resistor should be rated at 1W and the capacitor 400v.
• The resistor R3 is required to limit the current through the opto-isolator during the instant of time when it is conductive but before the triac has switched on.