Is a 1 nf capacitor really needed?
I would like to use a microphone with my propeller, so I looked at the schematic for it on the propeller demo board.
http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/PropDemoDschem.pdf
It shows using two 1 nf capacitors and I have no idea where to get them, so I was wondering if I could go without it or find a substitute.
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Pi Guy
http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/PropDemoDschem.pdf
It shows using two 1 nf capacitors and I have no idea where to get them, so I was wondering if I could go without it or find a substitute.
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Pi Guy
Comments
Mouser has several 1000pF 50V ceramic capacitors that should work (1000pF = 1nF). Other distributors would also have them.
Post Edited (Mike Green) : 11/2/2008 12:22:19 AM GMT
It's an extended form of that used by the old analogue joysticks, where the time taken to charge the capacitor is measured. And from that a reading is derived. It's actually somewhat better for two reasons - namely hardware timing is used and the inverting charge/discharge pulse width ratio is the measurement taken rather than the single cycle sawtooth method for your typical joystick.
So, yes the resistors and capacitors are vital. And as Mike said the layout of the board is also important to keep the relation between the capacitor voltage and the input high/low detection threshold stable.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
-Phil
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'Just a few PropSTICK Kit bare PCBs left!
I found some 100pf transistors from my PE kit and some other unknown capacitors (I couldn't find them on the parallax website) that say 10j on one side and 5a on the back. Can I use these in place of 1nf if I use multiple ones?
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Pi Guy
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
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Pi Guy