cs-20a
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| — | cs-20a [2020-05-18 02:44:29] (current) – created - external edit 127.0.0.1 | ||
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| + | ====== CS 20A AM-3 pressure sensor ====== | ||
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| + | Pinout & usage. | ||
| + | |||
| + | ===== Intro ===== | ||
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| + | These sensors are pretty popular in blood pressure meters. No datasheet exists, but reverse-engineering took only several hours. | ||
| + | |||
| + | ===== Pinout ===== | ||
| + | |||
| + | Top view (pins are not visible) | ||
| + | < | ||
| + | |||
| + | + calibration | ||
| + | | ||
| + | | ||
| + | |||
| + | 4 | ||
| + | 3 | ||
| + | 2 | ||
| + | 1 | ||
| + | </ | ||
| + | Pin numbers taken from Tensoval Comfort service printout. YMMV. | ||
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| + | Shielding: GND or N/C\\ | ||
| + | 4: GND\\ | ||
| + | 3: GND\\ | ||
| + | 2: TTL_OUT\\ | ||
| + | 1: Vcc +5V | ||
| + | |||
| + | ===== Usage ===== | ||
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| + | Upon connecting to GND and +5V, strobe signal appears on TTL_OUT. Frequency varies with pressure. rtl-sdr tuned to 24 MHz can pick it easily as alias. Arduino at 16 MHz cannot directly measure the frequency using interrupt handler. OTOH, a 86CH29BF @ 16 MHz can do it on AIN1/ECIN pin. I have not reverse-engineered the firmware nor tried some exact measurements with frequency dividers. It seems to be several MHz. | ||
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| + | ===== Internal schematics ===== | ||
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| + | Once the shielding is dismantled, a tiny board with 74HC02A (4 NOR gates) appears. They are configured as NOTs, as they have one pin grounded. Here is the schematics: | ||
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| + | {{ :cs-20a.png |}} | ||
cs-20a.txt · Last modified: by 127.0.0.1