Not a complete solution by any means, but my control program 'touches' a
heatbeat file each scan (20 seconds or so) and I have a separate monitor
program that looks at the heartbeat file and if it is more than a few
minutes old it sends me an email to say that something has gone wrong.
Both the control and the monitor programs run on the same server, so if
that fails I don't get notified. I have another server and I plan to
cross monitor to give more security, but haven't figured out how to do
it yet. Also in the control program I record the last good read
time/date, so I should be able to generate an alert on that, but haven't
got around to doing it yet.
Mick
On 13/12/11 22:40, Jacob Joseph wrote:
Hi.
I use some similar relay circuits myself, mostly for controlling large
heaters on a home brewery setup. I do worry about the failure modes
that could occur during use, moreso that the startup state. In
particular, some time ago, I had trouble with my 1-wire network that
would result in owfs hanging, and an inability to send the appropriate
"relay off" command. Now and then, I still lose communication with
individual devices. Even with the best of communications, I don't
particularly trust my computers or software to fail safely either.
I've toyed with timer circuits to shut off the relay if not reset, by,
say toggling the device state. I also have a couple of Pascal
Baerten's 1-wire microcontrollers that can make it easy to combine
this functionality. Where heaters are involved, separate, mechanical
thermostats can help. Overall, though, I haven't really settled upon
a protection mechanism that I really trust, and is convenient enough
to simply use with every relay.
What do others do about this?
Thanks.
~Jacob
On Wed, 14 Dec 2011 08:56:13 +1100
Nathan Hurst<n...@njhurst.com> wrote:
On Tue, Dec 13, 2011 at 06:53:29PM +0000, Mick Sulley wrote:
Yes that is pretty much the circuit I have used. The thing that feels
wrong to me is that the relay is energised until you turn the DS2406
output on.
Yes, use a pnp transistor instead, emitter to v+, base to ds2406 via a
suitable resistor, collector to the existing relay portion with diodes
etc. That would also result in much less power dissipation when the
device is off. Something like figure 3 here:
http://www.rason.org/Projects/transwit/transwit.htm
(but I wouldn't bother with the biasing 47k resistor)
njh
Mick
On 13/12/11 16:49, Zoff wrote:
Hi!
you can take a look at my 1wire relay. maybe its of some use to you:
http://1wire.zoff.cc/2010/09/18/31
it uses a DS2406 and a normal relay to switch high power loads
it can easly switch 220V loads, but i take no responsibility if you
house burns down!
i have 2 of those in use 24/7 since Sept. 2010, but only with low Watt
loads for now.
cheers,
Zoff.
Mick Sulley wrote:
Hi Jerry,
Your system sounds interesting. I also have a control system based upon
1-wire and Python which controls a solar (hot water) heating system
heating the domestic hot water and a swimming pool. My plan is to
extend it to control the whole of the central heating system as well.
Reliability is key to this sort of project and each time I have had a
failure (there have been a few!) I have tried to identify the root cause
and prevent it happening again, but this is an ongoing task.
I use a mix of home brew outputs based on DS2406, and X-10 to drive
valves and pumps. X-10 seemed the easy way to go but has not proved to
be very reliable and so I am moving to the DS2406 solution. What do you
use for driving outputs? It seems to be quite difficult to get
something that is fail safe, i.e. fails to off rather than on.
In terms of timing, my system reads all the temperatures, currently 26
sensors, then sets the outputs according to the logic and logs all the
data to a MySQL database. This takes around 20 seconds and it then
loops round again.
User interaction is by a local web page in PHP which reads and writes to
the database.
It runs on a server built from an old PC, located in the loft. I have
also built a second similar server, so that I can easily swap the plugs
over if the first server fails.
I have notices that many people use hubs to split their 1-wire networks,
currently mine is a single network with everything on it. I would be
interested to hear views on the use of hubs, do they improve reliability
or speed? Are there other advantages?
Cheers
Mick
On 12/12/11 22:19, Jerry Scharf wrote:
Hi,
I'm finally finding some time to write the next generation of my home
control system. I have had a number on control ideas I have wanted to
try out, and it is time to give them a try. The control and sensor
plant
in my house is close to ridiculously complex.
One fun thing is that I am getting rid of the ability for users to set
the room target temperature. Instead, there will be buttons that say
"I'm cold" and and "I'm hot". Push once if you are a little so, push
more than once if you are really so. The rest is figured out by the
control system.
This comes from my belief that 72F is a random control knob that has no
real meaning to a person in a room. If you want to prove this, go to
the
supermarket, pick up a room thermometer from the housewares aisle, then
go and stand in the section where the frozen food is. How cold do you
feel, what's the temperature say. Odds are you feel colder and the
temperature says it's higher...
I am building this in python/django (ruby on rails for python) an a
linux box. There is a database at the center of things and I want to
make the various parts to be independent processes. I want this so I
can
do things like replace the heating controls without impacting the
ventilation and cooling code at all.
The 1 wire reading is pretty easy, I create a process for each bus and
each process pulls the list to read, finds which ones are on its bus,
reads them and stores them into the database. Each process is self
scheduling (easy pieces built into python for this.)
I am having more trouble deciding on partitioning the controller and
driver parts. Part of this comes from how to make things stable and
simple, part comes from needing to decide where different functions
should be done.
I don't think each process should be accessing the control points
directly, these are mostly done via a mport box interfacing RS485 nudam
controller pods. Having each one setting up telnet sessions and writing
whenever they think it's reasonable does not seem like the path to
reliability.
I also want to be able to do things like:
Almost all controls are variable, and I want to use this. So when a
zone
calls for heat, it wants to open the water valves in a particular
stepped pattern, go to an higher than final flow rate for a period of
time (based on the lag of the zone) and then return to the final flow
rate until the temperature reaches the target.
This means that a single valve may be getting new position commands
every 10 seconds or so during the startup phase. I have plenty of
signalling bandwidth and there is plent of slow in the control
system, I
just don't want to swamp either the database or the cpu by having lots
of processes polling every second. I also don't want t be waiting 15s
for something to happen that was only supposed to be there for 10s.
I would like opinions on two things:
Do you think that things like start-up patterns should go in the
heating controller or the driver?
What method makes a reasonable balance of simplicity,
efficiency and
response for passing actions between the controllers and drivers?
All other kibitzing is also welcome.
jerry
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