Need to design a sensing circuit

• richt
In summary, the conversation discussed using a material called QTC to sense forces and the need for a circuit to switch on an LED at a predetermined force. Solutions such as using schmitt triggers or a window detector were suggested, along with using pressure switches and op amps. The conversation also mentioned the use of a force dependent resistor or load cell depending on the specific project.

richt

Hi iam looking for help with a college project i am doing, it is for sensing forces but the forces are only small. I am using a material called QTC( which changes from an insulator to a conductor when a force is applied to it). I am not doing electronics at college, so i only have a limited knowledge of electronics and circuits. How would i design a circuit that would switch on an LED at a certain predetermined force, then if the force is too high it would then switch on alternate LED. if this sounds at all possible could somebody suggest a circuit to use, as i have said i am a novice when it comes to electronics. I have come across schmitt triggers but i do not know how they work. thank you in advance.
rich

well...

you could have two series circuits coming from a source like a battery...with one of those pressure switches under some padding...going into the schmitt trigger turning on LED A

have the other pressure switch under some MORE padding under the first one, hooked up the same way. Might use a transistor to get the right Vcc for the Schmitt triggers.

Then just do some physics calculations, experimentation, and tweaking until you have the right padding to close the pressure switches with the correct force

That's how I'd do it but I'm a bootleg college student

You can either use the solution suggested by Number2Pencil or you can get away with ONE opamp that does the job for you: it's called a window detector, it is like 2 Schmitt-triggers in one ;)

Basically, window detector is a device which will trigger on two occasions which are predefined by a resistor network that surrounds the opamp. So basically you'll have two trigger levels with some margin (window) which you define by resistor-setting.

I would probably take the output from your sensor to two op amp comparitors. This way you wouldn't be loading you sensor.

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/compar.html#c1"

The comparitors will each have a threshold that you can set by your choice of resistances. (you could use a variable resistor; R1 in the linked circuit)

Regards

Last edited by a moderator:
You could use a force depandant resistor or a load cell depending on what you are doing.

1. What is a sensing circuit and what is its purpose?

A sensing circuit is an electronic circuit that is designed to detect and measure physical quantities such as temperature, light, or pressure. Its purpose is to convert these physical quantities into electrical signals that can be used by other electronic components.

2. What are the key components of a sensing circuit?

The key components of a sensing circuit include a sensor, which detects the physical quantity, an amplifier, which amplifies the electrical signal from the sensor, and a signal conditioning circuit, which processes the signal to make it suitable for use by other electronic components.

3. How do I choose the right sensor for my sensing circuit?

Choosing the right sensor for your sensing circuit depends on the specific physical quantity you want to measure, as well as the required accuracy, sensitivity, and range. It is important to research and compare different sensors to find the one that best suits your needs.

4. What are some common applications of sensing circuits?

Sensing circuits have a wide range of applications in various fields such as automotive, aerospace, medical, and environmental monitoring. They are commonly used in temperature and humidity control systems, pressure and flow measurement devices, and motion detection sensors.

5. How do I design a sensing circuit?

The design process of a sensing circuit involves several steps, including choosing the appropriate sensor, selecting the necessary components, designing the signal conditioning circuit, and testing and optimizing the circuit. It is important to have a thorough understanding of the principles of circuit design and to carefully plan and test the circuit before implementation.

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