Cat Food Restock alert circuit

One of my friend recently has got a Cat and he loves him so much. But due to busy schedule with business he couldn’t take care of it properly and only relies on his granny to feed him. The problem is that his Granny usually forgets to feed the cat properly and he asked If I can create a simple alert system that could help the granny remember to fill his cat’s food bowl. He knows a thing or two about Soldering so I designed this simple circuit that will alert when his Cat empty the bowl and alerts user to fill the bowl on timely manner.



The whole operation of this circuit is based on the pressure applied to the Cat’s food bowl by the food. This circuit uses a Pressure Sensor MPX2050DH1 to measure the pressure applied by the Cat food. This Pressure Sensor outputs a differential voltage that is proportional to the pressure applied to it.

The pressure sensor produces a Differential voltage in its output pins V+ and V- . The output voltage of this sensor is proportional to the pressure applied means the voltage increases with increase in pressure applied. Also this sensor is highly sensitive to changes in input pressure. We connect the positive output V+ to the non inverting input terminal of the Op-Amp. On the other hand we use a Potentiometer VR1 to provide the reference voltage to Opamp comparator.

The reference voltage should be adjusted in such a way when the food bowl is empty the voltage from Pressure sensor should not exceed more than reference voltage. However when the food is restocked the pressure sensor voltage should exceed the reference voltage. The buzzer was connected in such a way it will sound only when comparator gives low output. The comparator built using Opamp AD820R gives high output when sensor voltage exceeds reference voltage. This indicates the food is available in the bowl. When the cat had its food and after the bowl becomes empty pressure drops. Then reference voltage will be higher than sensor voltage. The output of Opamp goes low and the buzzer sounds until the food is refilled.


  1. Assemble the circuit and place the food bowl over the sensor so that it applies pressure over it.
  2. Start the POT VR1 from minimum position and adjusts to the edge where the buzzer should stop sounding if POT moves one more step.
  3. When you fill the food in the bowl, the buzzer should stop sounding.
  4. Use a heavy bowl and affix the sensor in order to make it work properly.
  5. Use a 100k or 1M POT instead of 10K, if it couldn’t provide the tipping voltage correctly.
  6. Best to use a mild sounding buzzer to not scare your pet off.


  1. 12V Battery
  2. AD820R Op-Amp IC
  3. BUZZER 12V
  4. MPX2050DH1 Pressure Sensor

Hope this circuit cheers up your Cat. Do check out other Alarm Circuits in our website and don’t forget to browse through our Electronics Circuit Library for 200+ Circuits of different categories.

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