The post explains an aquarium feeder timer circuit which sustains a set of continuous operations as per a predetermined timing sequence through the respective pot controls. The idea was requested by Mr. Mike.

Technical Specifications


I am trying to build a timer circuit to control an automatic fish feeder. It needs to operate on 12 volts. It needs to operate two relays. Both need to come on at the same time.

The first relay needs to shut off after 5.2 seconds. The second relay needs to shut off after 7 seconds. Then the process needs to repeat in 24 hours. Also can you convert 16 volts ac into 12 volts dc.

Thank you Mike

Circuit Diagram



The Design


As shown in the proposed fish feeder timer controller circuit, N1, N2 and N3, N4 are the four NAND gates from the IC 4093, configured as flip flop timer stages.

N1, N2 forms the 7 second delay timer, the period may be adjusted and set with the help of the 1M pot, identically N3, N4 is wired up as the second 5.2 second delay generator stage.

IC 4060 is designed as the 24 hour timer circuit for the required cycling of the desired time sequences.
When the circuit is powered, the 0.1uF capacitors at the inputs of N1 and N3 ground the respective inputs via the 100k resistors, rendering a negative latch across gate outputs, which in turn keep transistor relay driver switched OFF.

Now, for initiating the circuit the "start" button is pressed which reverts the gate latches to positive switching ON the relays simultaneously. This condition forces pin12 of IC 4060 to become high so that it stays disabled for the time being.

As per the proposed settings of the 1M pots, after about 5 minutes the capacitor at the N3 output charges up first forcing the N4 input to go high which yet again restores the latch to negative switching off the 5 second relay first, exactly in the same manner N2 relay follows and gets switched OFF after next 2 seconds.

The above situation causes the output of N2 and the input of N1 to go "low" which means now pin12 of IC 4060 is enabled at the required "low" allowing it to begin its counting until the stipulated 24 hour time is elapsed, when its pin3 goes high causing an automatic triggering of the above explained cycle.
The process now keeps repeating indefinitely as long as the aquarium feeder circuit is held in the powered state.

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