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cs-20a [2020-05-18 02:44:29] (current)
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 +====== CS 20A AM-3 pressure sensor ======
 +
 +Pinout & usage.
 +
 +===== Intro =====
 +
 +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)
 +<​code>​
 +
 +           + calibration
 +     ​CS-20A ​  03
 +     ​AM-3 ​  5 E 
 +
 + 4
 +  3
 +   2
 +     1
 +</​code>​
 +Pin numbers taken from Tensoval Comfort service printout. YMMV.
 +
 +Shielding: GND or N/C\\
 +4: GND\\
 +3: GND\\
 +2: TTL_OUT\\
 +1: Vcc +5V
 +
 +===== Usage =====
 +
 +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.
 +
 +===== Internal schematics =====
 +
 +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:
 +
 +{{ :cs-20a.png |}}
  
cs-20a.txt ยท Last modified: 2020-05-18 02:44:29 (external edit)