Hello, I'm working on implementing a circuit design I found on Electronics Hub. The schematic is attached. The circuit theory is that the two probes are placed in soil, which when dry will have high resistance and cause a large voltage drop. The output from the inverter will trigger the 555, which in turn will trigger the secondary 555 configured as astable monovibrator. The final pulse drives a PNP transistor which closes the relay connected to an electronic water pump. When the soil is wet, the probes conduct, and the circuit should open the relay.
My confusion is that the schematic I am working off of does not have the 7404 IC connected to ground, pin 7 is connected to one of the probes. This gives a floating voltage on all of the gates, and the circuit does not work as intended. Now if I touch the probe to ground (in reference to Vcc), the cycle triggers and the relay closes for a few seconds, then opens. So the circuit appears to be working, I just can't wrap my head around this grounding. It seems to me that the IC needs to have some sort of reference. Am I on the right track here, or missing something?
My confusion is that the schematic I am working off of does not have the 7404 IC connected to ground, pin 7 is connected to one of the probes. This gives a floating voltage on all of the gates, and the circuit does not work as intended. Now if I touch the probe to ground (in reference to Vcc), the cycle triggers and the relay closes for a few seconds, then opens. So the circuit appears to be working, I just can't wrap my head around this grounding. It seems to me that the IC needs to have some sort of reference. Am I on the right track here, or missing something?
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