Garden timer circuit with CD4000

  
The resulting timer circuit is made from a CD4060, includes an oscillator and a 14 stage binary counter, two CD4040's, which are 12 stage binary counters, a CD4012 Dual Nand gate and a CD4013 Dual D Latch. The CD4060 is connected to a 32768 Hz ECS 3X8 tuning form crystal. The 10 Meg Ohm resistor between CD4060 pins 10 and 11 are to bias the internal inverter into its analog region, and the 330 K resistor in series with the crystal is to limit the power to the crystal. This setup is directly from the ECS data sheet. The output of the 14th flip flop in the CD4060 appears on pin 3, and it is a 2 Hz square wave. A 2N4401 buffer drives a green LED with this square wave. When I see it blinking through the plastic window of the Irrigation System Controller housing, I know that power is on, and that at least the oscillator and first 14 counter stages are working.
Garden timer circuit with CD4000 - schematic

The CD4040's that follow the CD40406 divide the 2 Hz pulses to get the 24 hour cycle and the 34 minute watering period. When the counter counts up to 24.0355 hours, as decoded by the CD4012, both of the CD4040's are reset and the output of the CD4013 (pin 1) is set high to turn on the valve solenoid. To get a wide enough pulse to assure that all of the flip-flops inside the CD4040's are reset, the reset pulse from CD4012 pin 13 is passed through a low pass filter made of a 10k resistor and a 6 pf capacitor. A momentary push button, labeled "Resync" is connected to the output of the 10k and 6 pf low pass filter. When the button is pressed, it pulls the reset inputs of the CD4040's and the clock input of the CD4013 high to start a 24 hour timing cycle. The additional l0k resistor in series with the output of the 10k and 6pf low pass filter it to further limit current from the pushbutton to the input of the CD4012, which normally spends all but a few microseconds each day sitting at ground. I use the Resync button to set the time of day that the watering cycle starts. The CD4013 latch, the output of which (pin 1) goes high to turn on the valve , is reset 34 minutes after the CD4040's are reset, thus turning off the valve . The pulse to turn off the valve 34 minutes after the watering cycle starts, appears on Q1 of the second CD4040. If I wanted to the watering period to be 68.264 minutes, I would use Q2 (pin 7) of...



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