Need Help with My First Electrical Invention - Pressure Sensor Activation Device

[anorred]

Noob inventor needs help!

So in college I invented and marketed a simple device, and one of the doctors who promoted my idea called me and now I'm producing a product that he wants. I'm working alone and I just graduated so I need some help!

Basically, my device involves having to turn on a green light when these conditions are met: 3 pressure sensors reading at least .5 lbs/in2, and a switch being turned on. In other words, a green light turns on when all three pressure sensors have to be activated while the switch is on.

I'm thinking about using 3 transistors in series for each pressure sensor, and a battery + switch + LED on the main line. The pressure sensors need to be flat.. about .5 mm high.

This is my first electrical project! I need help. I'm very new to engineering so don't laugh. Where can I get these supplies? Are there pressure sensors that are that flat?

 

[jedishrfu]

why not use a raspberry pi or an arduino. they are cheap, programmable and extendable in case other conditions must be tested for. Arduino has the better IO but raspberry-pi runs linux. There is also the IOIO board which allows android devices to read and control external hardware although that combo is more expensive than an arduino or pi. Checkout the adafruit.com or sparkfun.com websites for more info.

 

[anorred]

I've never used an arduino board and I really know nothing about them. Are they hard to program? Although using simple electrical components would be easy, I would like the arduino experience if it isn't that hard. My system would basically look like:
p------|...|
p------|arduino|
p------|...|
s------|...|

How would I plug the switch and the pressure sensors in? Would they be soldered?

 

[D H]

anorred, read your personal messages.

 

[jedishrfu]

I've never used an arduino board and I really know nothing about them. Are they hard to program? Although using simple electrical components would be easy, I would like the arduino experience if it isn't that hard. My system would basically look like:
p------|...|
p------|arduino|
p------|...|
s------|...|

How would I plug the switch and the pressure sensors in? Would they be soldered?

I'm more familiar with the pi boards (see the book Raspberry PI in Easy Steps with a chapter on interfacing sensors and LEDs to the PI). There are also web examples at various sites just google for them. PI programming is in Python mostly but could be in C if really needed. The PI weakness is in few I/O ports vs Arduino which has many more and digital / analog control.

Arduino programming is done on a separate machine using the Arduino IDE and downloaded to the Arduino. The code looks very much like C code. There is no OS like Linux on board. Basically your program controls the whole thing. See http://en.wikipedia.org/wiki/Arduino

There is a large community of arduino developers and many books including the Arduino cookbook with a lot of simple recipes for doing common and not so common tasks.

 

[DaveH]

What is the range of the pressure sensor's input? You state a trip point at 0.5 lbs/in^2. What's the maximum input pressure?

How accurate do you want the trip point to occur?

It sounds like you need a pressure sensor that will output around a Volt at the 0.5 lbs/in^2 trip point. Depending on what sensor can be located (and your cost budget) you may need to amplify the sensed pressure signal. The output of each pressure sensor can then be compared to the trip point, ANDed together to turn on the green light. This would be simple (and cheaper) but not as flexible as the Arduino solution.

You mention providing this device to some doctors. Will your device be connected to a human patient? There are laws (requirements) concerning patient safety when connecting people to electrical devices. From a safety perspectived you'd be better off with a battery powered device. How long would a battery powered solution have to last?

 

[ScienceGeyser]

Check out omega.com for your sensor needs. They have sensors in just about any range you can imagine and a dozen different form factors as well. It sounds like you will be needing bare strain gauges to meet you size requirement of 0.5mm.

As mentioned by others, a microcontroller is probably the best way to go for a control circuit that is programmable and can handle the output of the sensors directly. Arduino is super easy to learn but a bit clunky for a finished product. TI makes a great little controller series called the MSP430. You can buy an EZ430-F2013 from TI for about 25 bucks and the target board unplugs and is small enough to be integrated into hand-held devices. The MSP430 series is also designed for low power battery operated devices.

Depending on the size constraints of your application, you could have no less than a thousand possible solutions the problem as presented. If you need more design advice, you will need to provide more detail about your application.