The I2C Remote Control refused to work.  Reading the analog pin on the PIC 16F876a seemed to work a couple of times after startup but failed after that.  It looked like the power to the 5v rail was still too low.

As I had allowed myself a slightly longer cable, it seemed reasonable that a combination of this and 78L05 were causing the problems.

I ditched both the 78L05s and wired in a 5v 2A PlugPack adaptor that used to run a Wifi Bridge – plenty of power!

Still the 16F876a processor refused to talk consistently to the I2C.  I checked that the bus was indeed working by plugging in the little i2c eeprom module I tested the original I/O bus with.  That worked no problems.

Looking at the I2C details on the www.sunspot.co.uk site and others, I wondered if the I2C pull ups were anything to do with the problem.  I was using 4k7 and I saw others using values as low as 2k2.

Substituting a pair of 2k2 resistors solved the problem, however, the 5v line dropped below the 5v mark.  Increasing them to 3k2 brought the 5v rail back to just under 5v and the PIC continued to talk to the I2C bus.

Lesson:  be prepared to tinker with the I2C pullups etc. when using different line lengths and slave devices.

The following program requires an update to the PIC I2C Slave software to set PORT B to output and the Remote Control On/Off lines connected to PORTB 0 and 1.  A 0v Line is also required between the two.  I continue to run the Mains Remote Control unit with its own 12v Battery although, the 12v supply to the router could also be used.

The following Blassic (Basic) program sets up the Router I2C software to talk to the PIC and then inputs “On or Off” from the console.  If the Response is On, PORT B0 is set high for a few seconds.  If it is ‘Off’, PORT B1 is used.

Here is the Program Listing

     10 REM Remote.bas
     11 REM Test The Mains Remote Control Via I2C
     12 REM Input On or Off then Switch the Plug On or Off
     14 REM Needs Update to PIC I2C software to Set Port B as Output
     20 REM
     30 REM I2C Control
     40 I2CAddress=34
     50 I2CData=35
     60 PIC16F876=46 : REM Address of Our Chip
     70 REM Commands
     75 PortB=1
     80 AnalogRead = 4
     90 PortA1Invert = 5 : REM Invert A1
    100 REM Begin
    105 INPUT "On or Off ",a$
    106 IF a$ = "On" THEN OnOff = 1
    107 IF a$ = "Off" THEN OnOff = 2
    110 POKE I2CAddress,PIC16F876 : REM Address the chip
    200 POKE I2CData,PortB : REM we are sending port be some data
    210 POKE I2CData,0 : REM ensure PortB All off
    220 POKE I2CData,PortB
    225 POKE I2CData,OnOff : REM Bit 0 = A1On, Bit 1 = A1Off
    230 GOSUB 800 : REM Delay long enough for the Remote Xmit
    240 POKE I2CData,PortB
    250 POKE I2CData,0 : REM and Stop Pressing Remote Buttons
    300 END
    800 FOR x=0 TO 4000: NEXT : RETURN
Ok

Update:
I was setting PORT B to 03 to turn off the power switch, ( B0 and B1 both HIGH) in error, the above code now only sets PORT B1 HIGH.

I also was getting random result trying to use a Blassic program to control the PIC 16F876a/Mains Remote from inside a shell script. That turned out to be a power problem, I’m only using a low power regulator for the 5v rail. This supplies both the USB Memory Stick, an LCD Display and the PIC Processor. When the USB Memory Stick is accessed, the power dips enough to reset the PIC Processor.

As the LCD Display was not needed for the Power Remote Control, I simply unplugged the display from the bus and the reduced power load allowed the rest of the systems to function.

I will now add a second 78L05 to the router and use that to power the bus.

It first sets up the I2C Address.

Then, Writes commands to read the PIC Serial Port, Toggling Port A,1 every New Line.

The program exits if a “!” is received.

midge# more PeekPokeTest.bas
10 POKE 34,46 :  REM our chip at 2e
20 POKE 35,3 :  REM select serial port
30 a = PEEK(35) REM Get a serial Char (0 if none ready)
40 IF a = 0 THEN GOTO 30
50 PRINT CHR$(a);
55 IF a <> 13 THEN GOTO 60
56 POKE 35,5 : REM toggle port A1
57 POKE 35,3 : REM back to serial port
60 IF a <> 33 THEN 30
midge#

Reading or writing to these chips involves sending the word address (0-255) before reading or writing the data byte.

After the first data byte has been read, simply reading from the chip will produce the next byte.

In the mods to Blassic on the Router, I have created a function to set the I2C chip address – “poke 34,ADRESSS” where ADDRESS is 0-255 will set up for reading or writing an I2C device The PCF8582C is at $50 (80 decimal) if all of its address lines are held low.

After this, 1 byte may be read from the chip by “x=peek(256+WORD)” where WORD = 0 to 255.

A byte may be written by “poke 256+WORD,data”

After Reading 1 byte as above, further bytes may be read simply by “x=peek (35)” inside the EEPROM, the WORD address is incremented after each read.

     +==u==+
  A0 1     8 5v
  A1 2     7 PTC / Not used
  A2 3     6 SLC
  0V 4     5 SDA
     +=====+

PCF8582C-2 Pinout

I2C Hardware

Here is the level shifter I’m using for the Router (3v) I2C interface (5v on Pic and other chips I have)

                 5v
                |
                |
                R
               4k7
                R
                |
SCL ---+--R220--+-----> 5v SCL
       |
     =====  Use the Same
      ZD\   For the Data
     /3.3\  Line
       |
       |
0v-----+---------------

The above has so far worked happily with an old philips 2048bit (256 bytes!) eeprom.

Pin Header (for breadboard)

1: 0v

2: 3v

3: 5v

4: KEY NC

5: TX (I/O Bus -> project)

6: RX (project <- I/O Bus)

7: LED3 GPIO8 I2C SDA

8: LED5 GPIO11 I2C SCL

I2C Software Settings

In the sunspot.co.uk Midge rom, the default I2C port uses different gpio lines.  To use gpio 8 and 11, the file “/etc/init.d/S99start_i2c” file needs changing:-

The line containing “insmod i2c-adm5128″ needs to read “insmod i2c-adm5120 scl=11 sda=8″

The Scart Connector Pins

+==============================+
| 1  3  5  7  9  11 13 15 17 19|(21) - - shield
|                               \
|  2  4  6  8  10 12 14 16 18 20 |
+================================+

Bus Connections & LED I/O Line Use.

I added extra power lines as the wire used is quite fine. The extra power and 0v lines are connected at the router, they are not linked on the Bus I/O board to avoid any ground loop.