Hi everyone!
I am a youth counselors in an educational program, and the team and I would like to start a business project together and need some help.

We want to build a circuit that connects to the car 12V power that does the following:
it has a weight sensor that is put under a baby car seat and whenever the car is off (No power from the car) and the baby is seated (and pressing something like a pressure sensor under the baby seat's fabric) there is a beep.

Can you help with the planning?
We need help figuring which component and parts we should use.
We know there must be a battery there, but can't figure out how to find a suitable weight sensor.
We also don't know how to plan and manufacture a circuit that gets power from the car and battery, and outputs the battery when ever the car is off.

Any help for this amazing group of teens will be appreciated!

Thanks!

 

Here's a link to a potential pressure sensor. I say potential because it's use depends on where and how any sensor would be mounted. Note that the bottom of this web page are links to six more pages of sensors. Click on this link.

 

Thank you!
How can I know how much weight is needed for it to work?

What about the other parts I need?

 

It tells you in the link I supplied. Anywhere from 100g to 10 kg. I would determine the exact range expected experimentally. How are you going to use the sensor? Read it with a micro or hard wire a couple of comparators?

 

Is there anything simpler? maybe something with just 2 metal plates and a spring? I really think we need a low-tech thing...

 

Is there anything simpler? maybe something with just 2 metal plates and a spring? I really think we need a low-tech thing...

You can get a pressure mat for a burglar alarm, but the comparator to sense the change in resistance is more complex than you'd need for just a switch. There's various pressure switches used in washing machines etc - hook one of those up to an air bladder under the seat pad.