Differences

This shows you the differences between two versions of the page.

@@ Line 1: / Line 1: @@
+====== 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
+</code>
+Pin numbers taken from Tensoval Comfort service printout. YMMV.
+Shielding: GND or N/C\\
+: GND\\
+: GND\\
+: TTL_OUT\\
+: 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 |}}

wiki