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
- 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.
Current revision (Rev.4B) of the motherboard (Sept 28th 2004):
Revision 4 schematic and layout (Aug 16th 2004):
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
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)
The Rev.4 boards as sent to the boardhouse have a tiny mistake:
The numbering of the capacitors skips C8/9.
|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.|