added pcb info

_docs/hardware_electronics.rst

@@ -1,10 +1,52 @@
 Electronics
 =============
 
+Electrical Block Diagram
+----------------
 
-try to make a file index who knows
+.. figure:: /images/electronics_diagram.png
+    :align: center
+    :figwidth: 100%
+    :width: 100%
+
+	PVP block diagram for main electrical components
+
+Overview
+----------------
+
+The PVP is coordinated by a Raspberry Pi 4 board, which runs the graphical user interface, administers the alarm system, monitors sensor values, and sends actuation commands to the valves.
+The core electrical system consists of two modular PCB 'hats', a sensor PCB and an actuator PCB, that stack onto the Raspberry Pi via 40-pin stackable headers (Figure \ref{fig:BOARDSTACK}).
+The modularity of this system enables individual boards to be revised or modified to adapt to component substitutions if required.
 
 .. toctree::
-   :glob:
+   :caption: Electronics:
+   Power and I/O <hardware.powerio>
+   Sensor PCB <hardware.actuators>
+   Actuator PCB <hardware.sensors>
+
+Power and I/O
+----------------
+The main power to the systems is supplied by a DIN rail-mounted 150W 24V supply, which drives the inspiratory valve (4W) and expiratory valves (13W). This voltage is converted to 5V by a switched mode PCB-mounted regulated to power the Raspberry Pi and sensors.
+This power is transmitted across the PCBs through the stacked headers when required.
+
+<ADD COMPONENT TABLE>
+
+Sensor PCB
+----------------
+The sensor board interfaces four analog output sensors with the Raspberry Pi via I2C commands to a 12-bit 4-channel ADC (Adafruit ADS1015).
+1. an airway pressure sensor (Amphenol 1 PSI-D-4V-MINI)
+2. a differential pressure sensor (Amphenol 5 INCH-D2-P4V-MINI) to report the expiratory flow rate through a D-Lite spirometer
+3. an oxygen sensor (Sensiron SS-12A) whose 13 mV differential output signal is amplified 250-fold by an instrumentation amplifier (Texas Instruments INA126)
+4. a fourth auxiliary slot for an additional analog output sensor (unused)
+
+A set of additional header pins allows for digital output sensors (such as the Sensiron SFM3300 flow sensor) to be interfaced with the Pi directly via I2C if desired. 
+
+<ADD SCHEMATIC AND COMPONENT TABLE AND PCB FILES>
+
+Actuator PCB
+----------------
+The purpose of the actuator board is twofold:
+1. regulate the 24V power supply to 5V (CUI Inc PDQE15-Q24-S5-D DC-DC converter)
+2. interface the Raspberry Pi with the inspiratory and expiratory valves through an array of solenoid drivers (ULN2003A Darlington transistor array)
 
-   ../assets/pcbs*
+<ADD SCHEMATIC AND COMPONENT TABLE AND PCB FILES>