Re: Electronic Wizards

[Pete Shew <pslists@xxxxxxxxx>]

Pictures at http://ph.groups.yahoo.com/group/ukha_d/photos/browse/e215
-
the station2.jpg shows the PIC with the CAN interface at the top and a
voltage inverter just beneath. I got the 128x64 displays from a guy on
eBay. I was hoping to use touch buttons through the plastic, but I
couldn't get a reliable enough separation, so I put some brass
paperclips through.

I like the 18F, but I had to build a ICD2 because my ICD doesn't work
with the later MPLAB. There are quite a few differences, but the switch
is easy enough. I just don't want to go back to the 16F877 in my PBX
(vague plans to upgrade that to an 18F4580 and add it to the canbus).
The 18F458 now seems to be obsolete, but the 18F4580 is a near drop in
replacement if you don't use the extended features.

I have so far only got three devices on the bus, the controller itself,
the first control station, and the CAN/RS232 device. I shall be adding
two more stations to provide temperature readings for the three zones
and local control. I chose PIC because of a) history with 16F devices b)
investment in debugging hardware, and c) PDIP form factor.

Canbus is a collision detect system using a balanced line. There is a
default status which is recessive and an asserted state which is
dominant. To send a message you start asserting dominant and recessive
bits onto the bus and checking that your recessive bits are not
overridden by another's dominant. As soon as this happens you back off
and let the other sender complete his message. Thus the higher priority
message doesn't detect collision and doesn't get interrupted. Part of
the frame is an acknowledge bit that at least one, and usually all,
other nodes assert if the CRC is good.

There is no master, and the concept of node ID is alien, being replaced
my message ID. It is more like a data identifier with any interested
node looking at the data, rather than a message being directed to a
specific node. In the car industry where CAN started it would be used
for e.g. a sensor sending oil pressure data that may be used by the
dashboard to display an indicator light and by the engine management
unit to monitor performance and decide whether to take remedial action.


Frank Mc Alinden wrote:
> Hi Pete
>
> Got any pics of your controller ;-)
>
> Havent  had a chance to play with my 18F  chips ......is it a big step
up
> from the 16F series ??
>
> Dave Mc Laughlin used Atmel /canbus  for his heating controller.....
>
> How many devices have you on your canbus network....??
>
> I believe there doesnt have to be a master on a canbus system ...??
and the
> canbus chips  ensure all message get onto the bus ???
>
> Frank
>
> ----- Original Message -----
> From: "Pete Shew" <pslists@xxxxxxx>
> To: <ukha_d@xxxxxxx>
> Sent: Tuesday, September 19, 2006 7:51 PM
> Subject: Re: [ukha_d] Electronic Wizards
>
>
>
>> My central heating controller system - now in phase 1 SWMBO
acceptance
>> - uses an LCD display with a PIC 18F458 and CAN interface back to
the
>> controller. I also have a CAN<->RS232 board connected to a
PC. I use two
>> pairs of CAT5 for connection, 12v power and CAN data.
>>
>> The reason for CAN was that it is much cheaper than Ethernet, and
>> although much slower was easily adequate for the traffic I need
with one
>> second updates of status and temperatures. The PIC has CAN
hardware
>> built in and free driver software, and the CAN driver chips are a
couple
>> of quid. At the moment I have around a 30m run of CAN bus wiring.
>>
>> The trick is getting a pretty looking enclosure ..
>>
>> Pete
>>
>>
>> Chris Miles wrote:
>>
>>> Have any the electronics guys ever thought about developing a
ethernet
>>> module with a small LCD display
>>> that can be plugged in anywhere in the house and displays
network
>>> information / current channel being
>>> sent down to the tv / music titles being transmitted via FM to
home
>>> stereo systems etc.
>>>
>>> Or maybe even using CAT5 medium to send power and a parallel
connection
>>> down to the display?
>>>
>>> Chris
>>>
>>>
>>>
>>
>>
>
>
>
>
>



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