Frequently asked questions about Paul's hottub.
What is this thing?
The hot tub is an octagonal whirlpool spa. It is not a Jacuzzi.
Jacuzzi is a trademark of another brand of whirlpool spa. This tub
is an Esther Williams Spa. It will hold eight people comfortably,
although it has held many more people than that in the past.
How does it work?
You use http, which runs the
httpd server,
finger,
which runs the fingerd server,
or email hottub@hamjudo.com which runs the mail server
on hamjudo.com.
The httpd server on hamjudo.com
Now I'm using NCSA httpd. It runs a CGI script for querying the hottub.
I used to use a home grown http server. It was started by inetd
whenever anyone queries the hottub via http. It ran a Perl program
that invokes a communications program that sends a "read analog"
request down a serial port to the Miniboard in the Hottub, through a 50
foot long cable. The Miniboard reads its analog sensors and sends back
the 8 values and a checksum. The comm program will try again if it
doesn't see a good checksum. Next the comm program has the Miniboard
make the "http" noise on its piezo electric speaker. Then the comm
program returns the 8 values to the Perl program. The Perl program
converts the 8 values into a (hopefully) meaningfull English status
message and sends it out.
The fingerd server on hamjudo.com
I wrote a little finger server. It is started by inetd whenever anyone
queries the hottub via finger. It runs a Perl program that invokes a
communications program that sends a "read analog" request down a serial port to
the Miniboard in the Hottub, through a 50 foot long cable. The
Miniboard reads its analog sensors and
sends back the 8 values and a checksum. The comm program will try again
if it doesn't see a good checksum.
Next the comm program has the
Miniboard make the "finger" noise on its piezo electric speaker.
Then the comm program returns the 8 values to the Perl program.
The Perl program converts the 8 values into a (hopefully) meaningfull
English status message and sends it out.
The mail server on hamjudo.com
Hamjudo.com runs smail 3.1.28. I alias hottub to invoke wrapper to invoke
hottub-answer.
I use wrapper.c to securely run a program from email. Hottub-answer,
the program that reads email, is derived from request-answer. Both
wrapper.c and request-answer are part of the Majordomo mailing list
manager which was written by Brent Chapman, brent@greatcircle.com.
Majordomo may be ftp'ed from ftp.greatcircle.com.
hottub-answer is a Perl program that invokes a
communications program that sends a "read analog" request down a serial port to
the Miniboard in the Hottub, through a 50 foot long cable. The
Miniboard reads its analog sensors and
sends back the 8 values and a checksum. The comm program will try again
if it doesn't see a good checksum.
Next the comm program has the
Miniboard make the "email" noise on its piezo electric speaker.
Then the comm program returns the 8 values to the Perl program.
The Perl program converts the 8 values into a (hopefully) meaningfull
English status message and sends it out.
What is the point?
I can check the hottub from inside my house or at the office.
I have a cron job that checks the tub periodically
and sends me email if something is wrong.
It gets cold in the winters here.
If the heater fails, the water could freeze and damage the tub.
What is the ozone generator?
An ozone molecule is three oxygen atoms instead of the normal two.
My dictionary (American Heritage Dictionary, Second College Edition)
says that
ozone is an unstable, powerfully bleaching, poisonous, oxidizing
agent with a pungent irritating odor.
I use ozone instead of chlorine or bromine to keep the water clear.
Ozone breaks down into normal oxygen after a few minutes in the water.
The ozone generator is a tube with an ultraviolet light. Air gets
sucked through the ozone generator and is pulled into the water. When
the UV light hits the air, it turns some of the oxygen into
ozone. The ozone in the water kills any single celled creatures
in the tub. It also has bleached my rubber ducky.
I use a photocell to check if the UV lightbulb is lit. If the computer
reports that the ozone generator is off, that almost always means that
the whole tub has no power.
What would cut power to the hottub?
I could have unplugged it, in order to work on it. The circuit
breaker might have been tripped. The ground fault circuit
interrupter (GFCI) in the house might have tripped. The GFCI
in the hottub might have tripped. If the tub got too hot, it
cuts the power. If the door to the wiring is opened, it cuts the
power.
What has broken in the past?
I left the pump on high with the cover closed and the pump generated
enough heat, so that the tub got up to 115 degrees and shut itself
off. The tub is rather well insulated.
I had a dehumidifier in the basement plugged into the same GFCI as the hottub.
The dehumidifier tripped the GFCI, thus shutting down the hottub.
If the filter gets really filthy, the flow switch will shut off the heater.
What is the backup battery for?
The backup battery powers the 6811 in the hottub when the main power gets
shuttoff. The backup battery is 8 AA rechargable batteries.
Can I change the temperature of the tub?
No, right now the computer in the tub only monitors, it does
not control it.
Could the computer short out and electrocute someone?
I measure everything from outside the tub. I don't have any
equipment directly touching the water. The temperature sensors
are on the outside of the tubs plumbing.
paulh@hamjudo.com