Home automation controllers

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... a PC is far too sophisticated for your job. Unless you need it switched
on anyway, it's a waste of energy.

Nathan and I have settled on a mini-pc for a smart whole house fan controller
that turns off an AC and runs a fan when it's cooler outdoors, and turns off
a heater and runs the fan when it's warmer outdoors and the air is dry enough
so there's no chance of condensation:

TU System 128mb ram + 512mb flash + Desktop Linux = $115 from

http://www.ewayco.com/51-embedded-s...-low-cost-pc-thin-client-embedded-system.html

It uses 15 watts. Is there a way to reduce the power, and does it
have 256 or 512M flash memory? It also comes with a wireless option.

A simple control using a few-$-Atmel controller is much better...

We found Atmel BASIC constraining, altho your displays seem nice.

and uses only very extremely little energy. My brother designed me a small
system that reads the stoarge temps to be shown in the bathroom. The system
has two CPUs with two LCDs (one in the cellar, one in the bathroom) and uses
a total of 6 W, including one backlighted LCD. Now I see the energy stored
in our water storage, easy to see whether better to take a shower, or
whether a bath is possible ;-)

I added some programing to show sunrise, sunset, azimuth angle, ... even the
percentage the moon is visible - just because the CPU was running anyway,
and I have lots of RAM (128 KB!) available. Such a simple system has
everything you would need - floating point support, a lot of I/O ports, ...

Does it have a Roman numeral arithmetic package? My first programming
language did, with error messages like "wrong Roman constant."

We are planning to use 2 $44 TAI 8540A 1-wire RH & temp sensors from
http://www.aagelectronica.com/aag/index.html?target=p_2.html&lang=en-us
and a $27 DS9490R 1-wire adapter, with OWFS as a 1-wire driver, and an X10
interface, eg the $69 2414u from http://www.smarthome.com/2414u.html or
Home Depot (are these too smart to program via linux?) with X10 controllers
for an AC, a heater, 2 fans and a damper, eg $11 15 amp AM466s from
http://www.x10.com/automation/am466_s.html

http://www.hobby-boards.com/catalog/index.php?cPath=24 has more fun stuff.

We are also looking at bwbasic, which appears to be about as old as gwbasic.
Here's an ASHRAE 55-2004 comfort calc done both ways:

50 CLO = 1'clothing insulation (clo)
60 MET=1.1'metabolic rate (met)
70 WME=0'external work (met)
80 TA=19.6'air temp (C)
90 TR=19.6'mean radiant temp (C)
100 VEL=.1'air velocity
120 RH=86'relative humidity (%)
130 PA=0'water vapor pressure
140 DEF FNPS(T)=EXP(16.6536-4030.183/(TA+235))'sat vapor pressure, kPa
150 IF PA=0 THEN PA=RH*10*FNPS(TA)'water vapor pressure, Pa
160 ICL=.155*CLO'clothing resistance (m^2K/W)
170 M=MET*58.15'metabolic rate (W/m^2)
180 W=WME*58.15'external work in (W/m^2)
190 MW=M-W'internal heat production
200 IF ICL<.078 THEN FCL=1+1.29*ICL ELSE FCL=1.05+.645*ICL'clothing factor
210 HCF=12.1*SQR(VEL)'forced convection conductance
220 TAA=TA+273'air temp (K)
230 TRA=TR+273'mean radiant temp (K)
250 TCLA=TAA+(35.5-TA)/(3.5*(6.45*ICL+.1))'est clothing temp
260 P1=ICL*FCL2=P1*3.963=P1*1004=P1*TAA'intermediate values
300 P5=308.7-.028*MW+P2*(TRA/100)^4
310 XN=TCLA/100
320 XF=XN
330 N=0'number of iterations
340 EPS=.00015'stop iteration when met
350 XF=(XF+XN)/2'natural convection conductance
360 HCN=2.38*ABS(100*XF-TAA)^.25
370 IF HCF>HCN THEN HC=HCF ELSE HC=HCN
380 XN=(P5+P4*HC-P2*XF^4)/(100+P3*HC)
390 N=N+1
400 IF N>150 GOTO 550
410 IF ABS(XN-XF)>EPS GOTO 350
420 TCL=100*XN-273'clothing surface temp (C)
440 HL1=.00305*(5733-6.99*MW-PA)'heat loss diff through skin
450 IF MW>58.15 THEN HL2=.42*(MW-58.15) ELSE HL2=0'heat loss by sweating
460 HL3=.000017*M*(5867-PA)'latent respiration heat loss
470 HL4=.0014*M*(34-TA)'dry respiration heat loss
480 HL5=3.96*FCL*(XN^4-(TRA/100)^4)'heat loss by radiation
490 HL6=FCL*HC*(TCL-TA)'heat loss by convection
510 TS=.303*EXP(-.036*M)+.028'thermal sensation transfer coefficient
520 PMV=TS*(MW-HL1-HL2-HL3-HL4-HL5-HL6)'predicted mean vote
530 PPD=100-95*EXP(-.03353*PMV^4-.2179*PMV^2)'predicted % dissatisfied
540 GOTO 580
550 PMV=99999!PD=100
580 PRINT TA,RH,CLO,PMV,PPD

19.6 86 1 -.4778556 9.769089

After removing the comments with something like

sed "s/'.*//;" gwfile.bas > bwfile.bas

and adding back 'THEN's which bw complained were out of spec, eg in

410 IF ABS(XN-XF)>EPS GOTO 350

we got

19.6 86 1 -0.4778564 9.7691115

which seems close enough

Nick

 

[[email protected]]

Have you considered one of the gumstix computers?

We just looked at that. No USB port?

... the base configuration gives you a couple of serial ports
and only uses about half a watt, less when idle. They can run Linux
and use CF memory.

Sounds good. I wonder if we can store everything in the TU flash and
power down the power supply 99% of the time.

http://docwiki.gumstix.org/Frequently_asked_questions/Heat_and_power

Then again, how fast a computer do you need for this kind of stuff?

A 60 Hz Turing machine might work

Have you considered a PDA? They come with their own display and are
pretty thrifty with the power requirements.

That's sorta where we started.

For that matter, you might even go so far back as the famous Radio
Shack Model 100 which crops up on Ebay for $20 or so pretty regular.
It only uses a watt or so and has basic built in.

Right... I bought one of those for engineering calcs when I worked
for Control Data, over humongous objections I have something
older in my attic with cassette tape I/O.

Nick

 

[Steve Cothran]

We added 4 1-wire temp sensors (although the number is not a
limitation), several A/D converters, 8 bit digital I/O, a CAN bus, two
serial interfaces.

From a guy that spent a few K$ automating his building, MOV's and any
other transient protection you can put on a piece of wire will pay
itself back over and over. Zeners ad resistors are your frind,too.

God hates silicon attached to wires. At least he does in Liberty,TN.

 

[Steve Cothran]

If you mean surge/lightning protection, you're correct, and this is used for
the controller ;-)

That was the meaning. Lightning surges burnt out most of my system
before I added surge suppression to all sensors,switches, and the
like.It only takes a short length of wire to have a larged induced
voltage on it from a nearby lightning strike.

I think to date I have lost 4 CCTV cameras, 3 LM35 temperature
sensors, several LED's, and 6 or so solid-state relays. All were
connected to some length of (shielded) wire or coax.