September 25, 2005
Assignment 3
The sensor which I am looking at is a Force Sensing Resistor (FSR)from Interlink Electronics.
The part number of the model is 402 and it is 0.5" in diameter. The approximate thickness of the sensor is around 0.018". The FSR is a polymer thick film (PTF) device which exhibits a decrease in resistance with an increase in the force applied to the active surface.
Applications
The sensor allows one to detect and measure the change in the applied force and also the rate at which the force is changing. It could detect contact or touch. Identify force thresholds and trigger actions.Its force sensitivity is optimized for use in human touch control of electronic devices.The FSR sensors have wide usage in the commercial and industry arena. The Applications range from medical, automotive to recreational and Industrial.
Electrical Characteristics
At the low force end of the force-resistance characteristic, a switch like response is evident. This turn-onthreshold, or ‘break force”, that swings the resistance from greater than 100 kΩ to about 10 kΩ (the beginning of the dynamic range that follows a power-law) is determined by the substrate and overlay thickness and flexibility, size and shape of the actuator, and spacer-adhesive thickness (the gap between the facing conductive elements). Break force increases with increasing substrate and overlay rigidity, actuator size, and spacer adhesive thickness.
At the high force end of the dynamic range, the response deviates from the power-law behavior, and eventually saturates to a point where increases in force yield little or no decrease in resist-ance. A saturation point is reached.
There are two two solder tabs on the sensor. One goes to the microcontroller and the other goes to +5V, and a fixed resistor to ground. The FSR feeds a varying voltage to the microcontroller. The fixed resistor provides a path to ground. The current will follow the path of least resistance, from the 5V source through the FSR to the microcontroller.
Click here for the user guide and more electrical interfaces with FSR's
Posted by Shagun at 06:02 PM
September 21, 2005
Assignment 2
To Output the Sensor changes over time using Processing.
It took me a while to get into the pcomp shop and firmware lab again. However not having taken any pcomp related last semester was a needed break. The slow process of getting the materials together, wiring the board to getting the 'blinky' to work was nerve racking. That done, I got down to looking for a suitable sensor. I chose the sensor Eric and I had used for the mailbot. It was a Sharp IR proximity sensor.
The code I used was Toms original code. I didnt improvise it atall except to change the threshold once in a while. The code on the pic was the Peak-finder code to, as the name suggests, find the peak value of the sensor over time. The pic communicates to the serial port of the PC. The Processing code graphs the value of the byte sent from the pic.
Posted by Shagun at 11:00 AM
September 20, 2005
Sensors in everyday life
In India, human beings act as sensors. They check the tickets before one boards the train, they man the traffic in the sweltering heat where there are no traffic lights. They would absolutely do anything done electronically in the rest of the world. Wonder why. Anyway, I miss the human interaction sometimes but not always. The convenience is immense when systems are electronic. Surprisingly my day doesnt involve as many sensor interactions maybe because I dont have an I pod or a coffee maker. Some are as follows
- Subway enty card scanner
- elevator doors
- Smoke alarms
- Security alarms
- Traffic lights
- Touch pad on the computer
- Shop doors
- I wonder if microwaves or dishwashers have any kind of sensors
- Remote control
- Door sensors in the trains
- Metal detectors
- I card scanner in the Bobst
Posted by Shagun at 12:08 AM