PHCC Motherboard

The PIC HomeCockpit Controller (PHCC) Motherboard

Description

The PHCC motherboard is the core component of the PHCC system. It connects to the computer via serial port (RS-232) or via USB.

A PIC18F452 microcontroller is used as the "heart" of PHCC. It is responsible for communicating with the PC via a simple protocol and it scans the Analog inputs as well as the keymatrix every few milliseconds.

The motherboard houses the following subsystems:

• 35 analog inputs (3 priority, 32 normal) in form of a pinheader with 3 terminals for each analog input

Potentiometers with a rating of higher than 10K Ohms is discouraged.  This is because the input impedance of the analog-to-digital converter on the PICs is 2.5kOhms.

The higher the potentiometer resistance, the more time is needed for proper conversion. With longer conversion times, the scanning rate goes down and has the potential to cause timing delays on reads.

• 16 connectors for 16 keymatrix daughterboards (64 inputs per board). For IDC flat ribbon cables.
• a RS-232 serial port (for Null Modem cables) with level converter (MAX232)
• a socket for USB interface board
• an I2C port
• a connector for Output daughterboards of "Type A" (DOA) using a 2x5 pinheader for IDC flat ribbon cables.
• and a connector for output daughterboards of "Type B" (DOB) using a 2x5 pinheader for IDC flat ribbon cables.

Schematic and Layout

Current revision (Rev.4B) of the motherboard (Sept 28th 2004):

Rev.4B Schematic

Rev.4B Layout

Revision 4 schematic and layout (Aug 16th 2004):

Rev.4 Schematic

Rev.4 Layout

Assembly Instructions

work in progress, pictures to accompany descriptions soon.

• text only, Rev.4: Motherboard_Rev4_assembly_tutorial.txt
• text only, Rev.4B: Motherboard_Rev4b_assembly_tutorial.txt

Download

See download page

Note about Resistors: all resitors are standard kind, ie. 1/4W, carbon film, +/-10% (Its generally a good idea to get lots of 10k and 330R resistors. the 10k are for pullups, the 330R for LEDs)

Board Errata

The Rev.4 boards as sent to the boardhouse have a tiny mistake:
The numbering of the capacitors skips C8/9.

Changes between Revisions:

Revision	Changes
Rev.4B	No functional changes. Added two Capacitors, one electrolytic for the incoming power supply, the other as a blocking cap, serving the second set of supply pins of the PIC. Improved spacing between the KEY1-KEY16 connectors. Moved blocking caps of the 4067's to be nearer the supply pins. Narrowed the capacitor lead pitch of the MAX232's caps. Gave the resistors a bit more space. Put in markings for LED polarity. Standardized Mounting hole positions.
Rev.4	Had to change pins used for analog inputs since microcontroller allows only consecutive ADC pins to be used. You have to start with AN0. (Lesson learned: always read the datasheet first :-) Added and beautified text and markings on component print (makes it look 'prettier'" :-) More space between pinheaders for DOA and DOB Fixed Debug LEDs. With Rev.3, only one of the two LEDs worked because of a thinking error. The 74HC/HCT154 is available in two formats, DIL24 and DIL24 narrow, now the board will accept both formats Reversed lines for lower nibble of PortB that control the 74HCT154. This makes the firmware easier. Old Rev.3 wiring is still supported in firmware via #ifdefs
Rev.3	aka. "The Prototype" First finished and prototyped board. Had to manually correct the ANx inputs(see Rev.4)
Rev.2	These were never finished/fully routed boards. They were results of tests of either trials of how to run the traces or with different chips.
Rev.1
Rev.0