Expansion Port Circuit Examples continued
Analog Inputs -
Analog inputs are inputs that can vary from 0 to 5 volts. While the Basic Stamp II doesn’t have a true analog input, analog signals can be read using a little trick. This is done by adding a capacitor to ground on a digital I/O pin and a resistive sensor to +5 volts. The sensor value can be read by first setting the digital I/O pin low to drain the capacitor, then the I/O pin is changed into an input, the resistive sensor will gradually charge the capacitor towards +5 volts. The time it takes for the signal to read a logic one (high) is the value of the sensor.
Analog Light Sensor
Basic Stamp II light sensor example code
'This routine demonstrates detecting light. The light level is 'read by determining the time it takes to charge the capacitor. 'The CDS photodetector changes resistance as the light 'intensity changes. This changes the current that is charging the 'capacitor. The output result is then output to the debug screen.
light var word | 'light variable. | |
main: |
|
|
pause | 500 | 'check every half a sec. |
low 2 |
| 'drain cap. |
pause | 50 | 'wait for cap to drain. |
rctime 2,0,light | 'time cap charging. | |
debug | ? light | 'send result to PC. |
More expansion information
Our space is limited here so make sure to visit our web site for the latest expansion application notes complete with program examples. www.robotics.com/arobot/projects.html
Also visit the Parallax web site which has an entire section dedicated to application notes for the Basic Stamp II. www.parallaxinc.com
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