Daox's diy arduino thermal differential controller

[Daox]

While I will probably do that (I'll try 6 degrees C), I do want to get this figured out so I can use it on future projects. I plan on making a similar controller for the solar hot water setup I am building and I'd like to get it figured out so I don't have issues with it once its up. It is going to have some very long sensor wire runs which will probably make the problem even worse.

[jeff5may]

Use the ds18b20 sensors. They are dirt cheap, and they don't drift around like the linear sensors can. Long wire runs are no problem either. The main thing I like about them is that they either work or they don't, rather than drifting or giving spiky readings.

[AC_Hacker]

Originally Posted by jeff5may

Use the ds18b20 sensors. They are dirt cheap, and they don't drift around like the linear sensors can. Long wire runs are no problem either. The main thing I like about them is that they either work or they don't, rather than drifting or giving spiky readings.

jeff5may,

I didn't realize that you had done any projects with 1-wire.

What kind of stuff have you done?

-AC

[jeff5may]

Well, lately, my youngest son has been in Lego League. The Lego brick controllers are built for a 5th grader, and he's in high school. So we rigged up the uno to do lego stuff. He can make his machines do anything for cheap, unlike the lego brick stuff, which is severely limited and highly expensive.

1-wire sensors are awesome. Depending on the device, they send and receive data just like an industrial plc unit (without all the extra wires). When the system powers up, they announce their presence. When they are told something, they do it. When they have something to tell, they ask permission. The processor is the master and everything else is a slave. The interface has collision prevention and detection built in, so data integrity is not a problem. And there are only 2 wires that go out remotely: power+data and ground.

I have prototyped up so much stuff with arduinos and 1-wire sensors, its hard to know where to start. Temperature and level sensors, addressable switches, light/proximity switches, etc. are all easy as pie. Need 12 temp and 2 level sensors (fuel gauge + rain gauge) plus a hysteresis temp control? No problem: use 12 ds18b20 thermometers, a ds2450 quad a/d converter, and a ds28ea00 digital thermometer with control logic. Tell the sensors how to act, monitor what you want to. Done.

The 1-wire sensors and bus are not really made for high-speed communications. If you want to exchange significant amounts of data, I2C or rs-232 or usb does that better. The bus and protocol are made for simplicity, so trying to load the 1 data wire with too much data will bog down everything. That being said, a lot of 8 bit data can be moved as readings and control signals, so don't be afraid the thing isn't going to react quickly enough to feedback or control signals.

[AC_Hacker]

Originally Posted by jeff5may

1-wire sensors are awesome.

It's puzzling to me that there's not a wide array of 1-wire devices. I'd think that there would be humidity sensors, and light sensors, etc.

Seems that they got a good idea going and just stopped.

-AC

[jeff5may]

The interface isn't made to handle lots of traffic. Error detection and correction isn't exactly robust. The interface was not made to control elaborate or complex functions. It was made so that micro-controllers could easily identify unique sensors and read their unique serial numbers. Data flow and control are just beneficial side effects, probably built out of headroom in a small instruction set.

That doesn't mean you can't make it do it, though. Dallas alone has a few devices made that can translate data to and from devices on the slave end. To interface with an array of analog sensors, they make a 4 channel a/d converter. The cool thing about this chip is that the analog inputs not used can be used as addressable switch outputs. They also make counters, to grab wind speed, motor rpm, and the like.

[AC_Hacker]

Originally Posted by jeff5may

Dallas alone has a few devices made that can translate data to and from devices on the slave end. To interface with an array of analog sensors, they make a 4 channel a/d converter. The cool thing about this chip is that the analog inputs not used can be used as addressable switch outputs. They also make counters, to grab wind speed, motor rpm, and the like.

So, you are telling me that I actually can buy a 4-channel a/d converter that is 1-wire ready?

And there are 1-wire ready counters?

And there are 1-wire wind speed sensors?

And there are 1-wire rpm sensors?

In what catalogs can these things be found?

Reason I'm interested is that as you already know, having already done countless Arduino applications, the 1-wire library only needs to be loaded once in a sketch, and then it could be used for very many devices.

At my local geek-lore repository, DorkbotPDX, absolutely nobody knows of any other 1-wire sensors.

This is very interesting news.

Where can I find these other 1-wire sensors?

-AC

[jeff5may]

Originally Posted by AC_Hacker

So, you are telling me that I actually can buy a 4-channel a/d converter that is 1-wire ready?
http://www.maximintegrated.com/datasheet/index.mvp/id/2921
And there are 1-wire ready counters?
http://www.maximintegrated.com/datasheet/index.mvp/id/2912
And there are 1-wire wind speed sensors?
http://1wire.org/Files/Awtrey/Schematic.htm
And there are 1-wire rpm sensors?

In what catalogs can these things be found?
You build them
Reason I'm interested is that as you already know, having already done countless Arduino applications, the 1-wire library only needs to be loaded once in a sketch, and then it could be used for very many devices.

At my local geek-lore repository, DorkbotPDX, absolutely nobody knows of any other 1-wire sensors.

This is very interesting news.

Where can I find these other 1-wire sensors?
You think them up and build them if not available.
-AC

1-wire devices are unbelievably easy to interface with. They either have analog or TTL level digital inputs and outputs. If you can breadboard a circuit, you can build a custom device using a 1-wire device.

HTTP://www.hobby-boards.com/store/pa...re-Basics.html

Looking at the stuff now, some of these devices have been discontinued. Here's a thread discussing current trends:
Weather Toys Discussion Forum • View topic - DIY 1-Wire Slaves

[jeff5may]

Here are some current pages:

http://www.atomicrhubarb.com/project/onewireswitch

Einfach-Relaisplatine zum Selbstbau

a simple counter:

http://www.shellypark.co.nz/?q=node/44

1wire controller on new nano tank biuld - Reef Central Online Community

[Daox]

I updated the code to add some additional smoothing functionality. Now, the program will compare each of the 10 sensor readings to the average of the last set of sensor readings. If the temperature varies more then 2 degrees Celsius, it sets that reading back to the average. After all the sensor readings have been evaluated, a new average is calculated. Seeing as how this sensor is in the attic, I don't think the temp swings should be that drastic. However, on the off chance that the temperature actually did jump up more than two degrees C, I added code to bypass the smoothing function and calculate the new average. This is also keeping in mind that this programming will be used in the future for other purposes that might have faster temperature swings.

I'll see how this new code works over the next few days.