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electronics-capsense-555
executable file
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electronics-capsense-555
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#!/bin/bash
cat <<'EOT'
Capacitive sensor unit with Active Shield (Driven Shield)
(Frequency output method)
+5
r2 2.2k |
.-\/\/-------*---* Frequency
| | | output r5 10k
| 4| 8| * *----/\/\---------*
| 7,---*---*--. | | |
*--------| | | | +5 |
| | | | | .\ * |
r1 \ 6| IC1 |3 | | | \| |
220k / *---| 555 *---* *----|- \ r6 47 |
\ | | | | \__/\/\--*-----* Driven
| | 2| | r3 10k | / shield
*----*---* | *--/\/\--*---+ / IC2 = TLV2461
| | | | | | | /|
c1 --- | `-----*----' | r4 \ '/ *-------------* Gnd
220pf ( ) | | | 1M / |
| | _|_ | \ |
| | = | _|_ _|_
_|_ | | = =
Gnd = | | Cap sense
*--------------------*--------------------------* plate
From:
https://www.electronicdesign.com/technologies/analog/article/21799482/driven-shield-enables-largearea-capacitive-sensor
1. In this large-area capacitive sensor, C1 and any parallel capacitance set
the frequency of the 555 astable multivibrator IC1, while IC2 buffers the
voltage at the capacitor to drive the shield plate. (The pin-outs for IC1 are
for the 'N' package.)
For IC2, resistors R3 and R4 decrease the buffered voltage by about 1%. This
prevents oscillation that may occur because of the external capacitance. R6 is
included since some operational amplifiers have difficulty driving a capacitive
load. IC2 should have a high gain-bandwidth product to allow a faithful
representation of the signal voltage without phase shift.
EOT