Absolute Maximum Ratings
KenM
Posts: 657
What is the absolute min and max voltage rating for an input pin on a BS2, and a BS2P?
Thank you.
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Ken
Thank you.
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Ken
Comments
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Jon Williams
Applications Engineer, Parallax
The reason for asking is that when using the Piezo film tab and the user "flicks" the tab, the input voltage·goes to about -0.5 volts when the zener forward biases.
Also, is that information in the Basis Stamp Manual? I looked but did not find a voltage spec.
I could have (should have) checked the SX docs....but had no info for the PIC.
BASIC Stamp Syntax and Reference Manual 2.1 • www.parallax.com • Page 453
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Ken
·· According to our engineers, the Zener Diode is not absolutely require due to the extremely low current of the Piezo device, as well as the high impedence of the I/O pins.· I asked for the Zener Diode to be included so that people wouldn't misunderstand the correlation between up to 70 volts from the Piezo and 70 volts from some other circuit going into the same I/O pin.
·· My thoughts were that if someone saw that the device can put out up to 70 volts and feed that into the I/O pin, then why not 70 volts from a battery, or what about 15 volts from a car electrical system.· It was to clamp the voltage to 5.1 volts, to be within the safe spec of the I/O pins from a technical aspect.·
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Chris Savage
Parallax Tech Support
csavage@parallax.com
Can I assume the same in the negative direction? With the device on a breadboard and no zener or rectifier large negative swings are also seen when the device is "flicked".
Yeah, 70 volts on an input pin....imagine that. "uhmmm my stamp does not seem to work anymore [noparse]:([/noparse]"
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Ken
Post Edited (KenM) : 7/12/2005 3:59:07 AM GMT
·· You are correct.· The bottom line is that the currents are so small, and the impedence so high, that the voltage is negligable in this case.· The Stamp Module needs to see the voltage move above 1.4 volts to be detected as a HIGH to the Stamp, and below 1.4 for a LOW.· For simple switching this is all you need.
·· An interesting thing to note since you have a scope is that this piezo device has characteristics which make it suitable for more than just what we're using it for here.· For example, if you turn your Volts/Div down to say 500mV, you may notice that blowing on the device, or even breathing on it generates low voltages.· Using an op-amp, or other amplifier, you could detect even minute changes in wind or vibration.
·· The device can also be used to some degree as kind of an accelerometer by loading the device (attaching a·mass to the sensor).· You can read up on some of this on the manufacturers website.· Intersting reading.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
Too cool!!!
As you suggested, the slightest breath on the device indeed generates enough voltage·over noise to be usable by an op-amp.
Not sure what I am going to do with the devices...but like the SX52 proto boards and the price....I just had to have some !! ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Ken