Heating system controller

Krahmer

Hi.· I'm new to the forum, and new to the world of the Stamp.· I'm also a very novice electrical guy.· I am attempting to design my first stamp controller application, and would like some input.· I'm looking at using the Javelin.··I will have the following inputs to·monitor: 10 temperature sensors and·6 zone valve end switches.· I will have outputs of three pumps and six zone valves.·

For the inputs, I was looking at using 2 ADC0838 ADC's.· For the temp sensors, I was going to use AD592's with resistors to feed the ADC.· The zone valve end switches basically provide a 24VDC feedback that the zone valve is completely open.· I was going to use a 1/6 voltage divider to bring that down to a 0V/4V signal to feed the ADC.

For the outputs, I was looking at using 2 8574's on one bus.· One would run the 6 zone valves.· Is it correct that I can take the output from·a pin·on the 8574, feed it to a (transistor | mosfet), which would feed a relay, which would energize the pumps?· One pump is 120VAC, the others may be as well, or may be 12 or 24VDC.· The datasheet on the 8574 says the pins stay latched, so I'm assuming I can do that, and just send a 0 down the line when I want them to shut off.· The zone valves are basically just 24VDC solenoids, and would operate the same way.

I would also be using a 1302 real-time clock chip, and an LCD display.· It looks like this will take 14 of my 16 I/O pins, and do exactly what I want it to.· Are my assumptions correct, or am I way off base?· Thanks.·

steve_b

What kind of environment is this? Home?
The reason I ask....if you run long cable lines from your temp sensors to your ADC you might have a lot of noise to deal with. however, if you digitize at your temp sensor any noise can be easily cleaned up with an R/C filter.
You might look at DS1620 which sends rs232 data out. You can also use these temp sensors as thermostat controllers (you can program the IC to switch on a given temp reading).

As far as pin counts....you can get one of those popular MUX chips that will use 3pins and give you 8. A bit more code is involved but worth the extra pins. for the life of me I can't remember the IC name/number and don't have it saved on my laptop. A quick search of the forum will probably reveal what it is!

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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Orion

If you choose to stay with the adc there are still things you can do. Use shielded cables, software smoothing/averaging, small cap to ground at the adc input, carefull routing of cables. I take the last three samples and average them for the final reading. Also if a sample is x% different from the average, it is discarded. Example: last three readings where 75, 74, 76 and the current is 50, then it is tossed and the average is used instead, until next adc read.

Krahmer

Thanks for the pointing out the possible noise issue. I hadn't thought of that at all. I would have preferred to use another type of temp sensor, like the 1620 you mentioned, but I only have 2-conductor thermostat wire running to my thermostat locations. This is for my house. I have an in-floor radiant heat system with 6 zones. I have an on-demand hot water heater for a heat source, so I want to write this controller to increase efficiency by controlling the on-off cycles with better detail.

The MUX chip you mention is the 8574 that I referred to. It is an I2C chip, and only requires two pins from what I can tell, and you can daisy-chain up to eight of them.