The design goals of this circuit were efficiency, simplicity, reliability and the use of field replaceable parts. The DAS1 circuit is designed to work in conjunction with the SCC3 Solar Charge Controller, which is also available in Kit form.
When using a solar-charged battery with the DAS1 circuit, the battery's amp-hour rating should be matched to the photovoltaic panel's charging capacity and the desired lamp load's discharging capacity.
Supply voltage: 12V (nominal). Maximum lamp control current: 10A at 12V. Day/Night battery current drain (off): < 10 microamps Day battery current drain (auto): 5mA @ 12.8V Night battery current drain (on or auto, no external load): 27mA @ 12.8V
See the full DAS1 kit specifications for a more detailed list.
Regulator VR1 lowers the supply voltage to a constant 8V for powering the control circuitry. Op-Amp IC1a is wired as a voltage comparator circuit, it functions as the Low Voltage Disconnect. When the supply voltage is above the LVD setpoint, the sense line on IC1a pin 2 is above the reference voltage on IC1a pin 3 and the output of IC1a is low. When the supply voltage drops below the LVD setpoint, the output of IC1a goes high, disabling the light sensor circuit. Resistor R11 provides hysteresis action on the LVD circuit, preventing oscillation when the supply voltage is near the LVD setpoint. Variable resistor RV1 adjusts the low voltage disconnect setpoint.
Op-amp IC1b is wired as another voltage comparator circuit, it measures the light level on pin 6. Bright light on the CdS cell cause the voltage on pin 6 to rise above the reference voltage on IC1b pin 5, this in turn causes the IC1b output on pin 7 to go low. Low light on the CdS sensor causes the voltage on IC1b pin 6 to go below the pin 5 reference voltage and the IC1b output will go high. Resistor R6 provides hysteresis to the light sensor circuit, preventing light flicker at dusk and dawn. Variable resistor RV2 adjusts the dark turn-on point.
The IC1b output signal is sent to transistor Q1, which pulls the gate of power MOSFET Q1 down (on) or up (off). Q1 controls the flow of current from the supply to the external load pins on CN1. The two white LEDs are connected across the external load pins through current limiting resistor R1.
[]Set the variable voltage DC power supply to 11V DC. If you don't have an 11V supply, you can use a rechargeable battery that has been discharged to 11V. []Connect the board's BAT - terminal to the DC supply's - terminal. []Connect the board's BAT + terminal to the DC supply's + terminal. Use a Red positive (+) wire and a black negative (-) wire for the battery wires. []Turn the three position switch to the On (right) side. The potentiometers have a full range of 25 turns, they make a clicking sound when they are at the endpoints. []Turn the LVD setpoint potentiometer RV1 counter-clockwise until the two white LEDs turn on. []Slowly turn RV1 clockwise until the LEDs turn off. The low voltage disconnect setting is now at 11V DC. For other LVD setpoints, adjust the power supply to the desired LVD setpoint and repeate the last two instructions. If you raise and lower the variable DC supply's voltage, the LEDs should turn off at 11V and on at slightly higher than 11V due to the circuit's hysteresis action. []Turn the three position switch to the Auto (left) side. []Make sure the CDs cell is attached to the 2 pin connector. []Turn RV2 counter-clockwise 25 turns, the LEDs should turn off. []Place the CDs sensor in a dark location or cover it with a black plastic container. The light level on the CDs cell should be at the darkness where you wish the DAS1 to turn on. []Turn RV2 clockwise until the LEDs turn on. []Remove the cover from the CDs cell, the LEDs should turn off. If you cover and uncover the CDs cell, the LEDs should turn on and off, the off light level is darker than the on light level due to the circuit's hysteresis action. []You may want to fine-tune the RV2 darkness turn-on setting at dusk after the DAS1 board has been mounted in a permanent location.
When the DAS1 switch is put in the ON position, the two onboard LEDs and the external lamp(s) will light up. When the DAS1 switch is put in the AUTO position, the two onboard LEDs and the external lamp(s) will light up if the CDS sensor is in the dark.
If the DAS1 is operated from battery power, the onboard and external lamps will turn off as soon as the battery voltage drops below the LVD setpoint. The low voltage disconnect function works for both ON and AUTO settings.
