View source for APC7921

== APC7921 overview==

The APC7921 is an 8-port Power Distribution Unit where every port is switchable.
It provides a way to control the outputs via serial and/or ethernet (10/100Base-TX).
There is also a provision to sense and display the total amount of power going through the device via a current-transformer and a 2-digit 7-segment display.

A status-led provides extra device-status, a button allows for basic interaction. A pinhole-reset-button allows resetting the device without cutting power.


== The front-panel==
Front
* Ethernet w activity-leds
* Serial
* 2x 7-segment display
* 1x 3-color LED
* Button
* factor-reset-switch (hole)
* 
* 8x female outlets
* 8x leds
* 1x male inlet
   
==Schematic overview==
<PRE>
                          FRONT
+---------------------------------------------------+-----+
|  Controller | |                                   |     |
+-------------+ |          Relay board              |     |
| IN     OUT    |J131                          J132 |     |
|               +-----------------------------------+     |
|                     +-----------------------------+     |
|                     |     PSU Board               |     |
|                     |J231             J266        |     |
+---------------------+-----------------------------+------
                        BACK
</PRE>

== Components overview ==

=== PSU module ===
PSU -> PSU -> controller wiring

The PSU board has two identical PSU's onboard that provide 24VDC
The right-most PSU also has a set of pins used for connecting current-transformer circuitry to the controller.
The left-most PSU only has 2 pins connected for 24VDC, nothing else.

=== PSU -> PSU -> controller wiring ===
10-wire flat-cable with 2mm pitch 2x5 connectors runs from J266->J231->Controller-IN
See connector J266 and J231

=== Controller  ===

The controller provides ethernet and serial connectivity; as well as a 2-digit display and a 3-color status-led to indicate errors and/or amperage. It also has a single button to interact with the device, as well as a pin-hole switch that allows for factory-resets.

Main things to replicate:
* 24VDC 'merging'
* Faulty PSU detection
* Ethernet function
* Serial function (if desired)
* 24VDC->3.3VDC conversion (for relay-board logic)
* I2C bus to control relay-board
* Adress-bus lines (can be hard-wired)


The controller drives the relay-board with a similar 10-conductor flatcable with 2x5pin 2mm headers.
It provides 24VDC and 3.5VDC power to the relay-board with seperate GND's.
It also provides an I2C bus (SDA/SCL) and 3 'address-lines'.
See connector J131

=== Relay board ===

There are 2 main parts to the relay-board. The IO-circuit and the relay-circuit.

==== Relay-board IO circuit ====


[[File:APC-Logic.jpg|thumb|PCF8574 and 7402's]]

The relay-board uses a PCF8574 'Remote 8-Bit I/O Expander for I2C Bus' to provide 8 outputs that drive the relays.
It is powered with 3.5VDC from the controller-board which creates it from the 24VDC available there.
The PCF85674 has 3 address-strapping lines A0,A1,A2 that allow selecting the I2C slave-addresses for both READ or WRITE operations. See table later in the document.
In single-board operation, strapping all pins to L would put the READ address at 0x41 and WRITE at 0x40
The relay-boards can be daisy-chained by connecting a next board to the J231 of the first.
For this to work, however, at least one, and at most two, address-lines will need to be strapped H
The reason for this is the manner in which the A0-A2 lines are presented on the J231 connector. They are shifted one pin, 

<PRE>
Signal    J131         +-------------+      J132
  A0        7 ---------|---------+   +------  7   
  A1        9 ---------|--+      +----------  9
  A2       10 ---------+  +----------------- 10
</PRE>

The PCF8574 provides 8 outputs that drive the relays using a circuit that first INVERTS the data via a NOR port (one pin strapped to ground, the other connected to the PCF8574) before running to one of the 8 relay-circuits that switch the 220VAC power provided to one of the 8 output terminals.
The 8 NOR ports for this setup are provided by 2x 7402 IC's and seem to function both as a signal-conditioner as well as a way to ensure the power-on state is 'on' for each of the relay circuits (needs to be verified).

==== Relay-board relay circuit ====

Each of the 8 relay-circuits is identical and consists of:
 
* A small switching-transistor driven from a NOR-gate, switching 24VDC 
* NMBT222A, marked 7CP
* A Relay-coil being driven by the switching-transistor
* A flyback diode across the relay in reverse-polarity for circuit-protection
* A smaller diode-array that seems involved in driving the LED somehow.
* BAV99, marked A7W
* An LED
* A series resistor to current-limit the LED

== Pinouts of connectors ==

=== J266 PSU1 ===
(right, next to current-transformers)
<PRE>
                 +----+
              NC |10 9| NC
        GND PSU1 |8  7| Sense Phase B
      24VDC PSU1 |6  5| 24VDC PSU1
Center of 3phase |4  3| Sense Phase A
Center of 3phase |2  1| Sense Phase C
                 +----+
</PRE>

=== J321 PSU2 === 
(left, on edge of board) 
<PRE>
           +----+
24VDC PSU2 |10 9| GND PSU 2
           |8  7|
           |6  5|
           |4  3|
           |2  1|
           +----+
</PRE>


Note: GND PSU1 and GND PSU2 are connected together via screws that fasten PCB to chassis.


=== J131 Relayboard input ===
(on relais PCB , left side)
<PRE>
 J131 and J132
  +----+
  |1  2|
  |3  4|
  |5  6| 
  |7  8|
  |9 10|
  +----+


	J131		PCF8574
1	GND IO		8         
2	GND relais
3	VCC IO		16
4	SDA IO		15
5	24VDC relais
6	24VDC relais
7	A0 IO		1
8	SCL IO		14
9	A1 IO		2
10	A2 IO		3
</PRE>

=== J132, relay board OUT === 
<PRE>
On right side of relay board

1	GND IO
2	GND Relais
3	VCC IO
4	SDA IO
5	24VDC RELAIS
6	24VDC RELAIS
7	A2 IO
8	SCL IO
9	A0 IO
10	A1 IO
</PRE>

=== PCF 8574 DW (16 pin) ===
O = Pin 1 marker

<PRE>
       +----------+
  A0  -| 1 O   16 | VCC (2.5-6vdc)
  A1  -| 2     15 |- SDA
  A2  -| 3     14 |- SCL
  P0  -| 4     13 |- _INT_
  P1  -| 5     12 |- P7
  P2  -| 6     11 |- P6
  P3  -| 7     10 |- P5
  GND -| 8      9 |- P4
       +----------+
</PRE>