Build Your Solar-Powered Digital Clock Masterpiece

Description

This is a combined digital clock timer and solar panel charge controller designed to maintain a deep cycle battery from a solar panel. The timer output is utilized to control a 12 volt load for a 32 minute duration each day. The initial start time is set using 9 dip switches and concludes 32 minutes later. The 32 minute duration is determined by selecting the 5th bit (2^5 = 32) of a 4040 binary counter (pin 2). The timer circuit also incorporates a manual toggle switch, enabling manual activation or deactivation of the load, and automatically shuts off the load after 32 minutes. The duration can be adjusted to values such as 8, 16, 32, 64, 128, or 256 minutes by selecting the appropriate bit of the counter. The timer circuit is depicted in the lower schematic above the regulator.

The core clock circuit (top schematic below) operates similarly to the binary clock (on another page) and employs 7 integrated circuits (ICs) to generate the 20 digital bits for a 12-hour time display, including AM and PM designations. A standard watch crystal oscillator (32,768 Hz) serves as the time base and is divided down to one half second by a 4020 binary counter. One half of a 4013 data latch is utilized to divide the 1/2 second signal by 2, producing a one-second pulse that drives the seconds counter (74HC390, colored purple). The minutes are incremented by decoding 60 seconds (40 + 20) and subsequently resetting the seconds counter to zero, while simultaneously advancing the minutes counter. The same procedure is applied to increment the hours. The other half of the 4013 latch is employed to represent AM or PM, and this is toggled by decoding 13 hours and resetting the hours to 0, followed by advancing the hours to "one".

The clock display circuit is illustrated in the second drawing below and utilizes 6 additional ICs for decoding the binary data and driving four seven-segment LED displays. A single 3904 transistor powers the 10s of hours digit. Two multiplexer circuits (4053) are used to manually select either minutes or seconds for the right two display digits. The two switches, shown between the 4053s and beneath the left 4053, are both connected to a single DPDT switch, which selects either seconds or minutes for the 1X and 10X digits. This switch is positioned in the seconds position, and the hours digits are blanked with a low signal on pin 4 of the 4511. The display can be toggled on or off (completely blank) utilizing a set/reset latch created by a couple of 74HC00 NAND gates. A momentary DPDT switch controls the latch and toggles the display on or off. The other pole of this switch is used on the upper drawing (connected to the run/stop switch) to set the hours and minutes. Consequently, this switch performs both functions of blanking the display and setting the time. The run/stop switch is shown in the normal running mode, supplying a low signal to a NAND gate, preventing accidental time setting while the clock is running. The run/stop switch also activates the display (through the diode D2) when in the stop position. The process for setting the clock involves setting the (run/stop) switch to the stop position, and the (seconds/minutes) switch to the minutes position. Subsequently, toggle the momentary switch to set the minutes and hours of the current time plus one minute. The clock can then be started with the run/stop switch at precisely the right time (+/- 0.5 seconds).

The voltage regulator, illustrated in the lower drawing, maintains the battery voltage at 13.6 volts and simultaneously supplies the clock and timer circuits with 4.3 volts. The charge LED indicator only illuminates when the regulator is delivering maximum charge to the battery. When the battery voltage reaches 13.6 volts, the regulator reduces the current to the necessary level to maintain the voltage, and the charge indicator turns off. The unit I built also incorporated a battery condition indicator (voltmeter using 4 LEDs) to indicate the battery condition, allowing for the detection of regulator failure through the charge indicator LED turned off and fewer than 4 LEDs lit on the voltmeter. The 4 LED battery condition indicator is shown on another page.

Basic Clock Circuit

Clock Display Circuit

Clock Timer Circuit

Voltage Regulator (13.6 volts)