Pressure Cooker Whistle Counter Circuit

This circuit is designed to sense the whistles from a pressure cooker and count the number over a digital display. The system relieves the user from the stress of constantly monitoring the cooker and from manually counting the whistles.

The idea was requested by Mr. P.K. Bajpai

Design Concept

In many of the Asian countries rice is the staple food and to cook rice efficiently a pressure cooker is normally employed. We all know that a pressure cooker is preferred since it is able to cook food quickly through its high steam pressure inside. This saves energy and time both for the user.

Another advantage of this special cooking vessel is the facility to adjust the cooking degree or consistency of the food ingredient through an audible alarm in the form of whistles, also created by steam pressure.

The number of whistles allows the user to understand and optimize the texture and the efficiency of the food inside the cooker, and if this is not correctly estimated results in a bad quality food or sometimes even complete destruction of the food.

Electronic Counter for Counting Whistles

As per the request I have designed a simple and cheap whistle counter circuit that will relatively accurately respond to cooker whistles and trigger a digital counter for generating the data over the display.

How the Circuit Works

Referring the image above, the design is basically built using two stages, a sound sensor circuit comprising T1, T2, T3, and a digital clock counter circuit using IC 4033.

The original circuit of the sound sensor was actually an ordinary MIC based amplifier designed to pick all sorts of sounds, and therefore the same design did not appear desirable for this particular project, since here I needed the device to sense only the high pitched whistles and not any other form of sound disturbances.

To modify the sound sensor into a customized whistle sensor I initially thought of applying LM 567 concept so that it filtered only the specific sound frequency.

However I did not want to make the design too complex, rather wanted to keep it simple and cheap, yet reasonably accurate.

This led me to think of an alternate solution using an opamp based high pass filter, but even this could have made the design complex, therefore ultimately I ended up designing a passive high pass filter using a capacitor and the resistor network for accomplishing the purpose.

You can see this inserted in the form C2/R7. This network makes sure that the only the high pitched, high frequency noise is able to pass through T2 and reach T3 for further amplification.

Other lower frequencies will be simply cut off and not allowed to cross the C2/R7 stage.

Before drawing the schematic I confirmed the result by imitating and  creating sharp verbal hissing sounds over the MIC, I was happy to see the connected LED effectively turned ON only to these noises, whereas the other normal loud sounds hardly succeeded to produce any effect. This confirmed the sound filter stage perfectly.

However the counter is not practically checked by me, but I can assure that it will work, since the design is a standard IC 4033 digital counter application design.

Parts List

R1 = 5k6,
R3 = 3M3,
R4, R8 = 33K,
R5 = 330 OHMS,
R6, R2 = 2K2,
R7 = 470K, R9 = 10K,
R10 = 1K,
R11 = 470 Ohms,
C1 = 0.1uF,
C2 = 330pF,
C3, C5 = 0.1uF ceramic
T1, T2 = BC547,
T3 = BC557,
IC1 = 4033
Mic = electret condenser MIC.
Display = 7 Segment Common Cathode Type,
Push Button = Push to ON type, Battery = 9V PP3 with switch

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