Very new - need good advice

[micro1]

Hi everyone and happy new year. I am following through with my resolution to complete a project, but will need to do some learning first.
I have a Basic Stamp microcontroller kit, but don't know if it will work for what I need. What I am attempting to do is pretty simple (I think)

I need to measure air temps in 3 different ares simultaneously. (2 airstreams and the mixed temp where they meet)
I need a microcontroller (or something) to receive this information, receive a desired percentage of air of one of the airsteams input by a user on a keypad
from 0% to 100% with displays of desired % of air, actual % of air, and temps of the 3 remote probes - then based on the temperatures of the airstreams I need the micro to send voltage to a motor attached to a damper which controls the % of desired air from the airstream we are trying to control and adjust it (in the correct direction which may vary depending on air temps) and re-read and basically loop until the micro has determined the mixed air temp would equal the percentage of desired air from the airstream we are trying to regulate. Basically setting the % of air by a mixed air temp.

My question is will something like the Basic Stamp work for this ? Can I connect the necessary hardware including thermistors or digital temp. sensing devices to this board? Can a code be written with the Basic Stamp to perform this task? What would the best alternatives be to build this device?
Any help is greatly appreciated.
Happy 2007 - let's make it a tremendous and prosperous new year!

 

[mvs sarma]

Hi Micro1,

Welcome to the Fourm and best of 2007.

temp measurement is generally a slow process. if basic stamp is cheap you may use it. wrinting program ib basic is ok if you dont want to write in assy language. PICs can be used. If , in case you are new, you may gothro, Nigel's tutorials on PIC


PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

[dknguyen]

Sounds like you have a good handle on things. All you need to do is learn how to code for a Stamp and find a temperature sensor. Controlling the LCD display and the motor should follow pretty naturally. YOu probably already have a method to control the motor right? SO that's not much of a problem. Even if you don't it's not.

How far away are these streams you are trying to measure? And how hot might they get? If it's far away or hot you might need to get a thermocouple wire (and a thermocouple conversion IC). I'd recommend you not use a thermocouple since I know of no TC ICs that are through-hole and you probably don't want to deal with surface mount right now. If you did use one it would either be analog (you would use an ADC on the BASIC stamp so it wouldn't change anything like with a thermistor) or it would require you to use a serial protocal which you have to do with the LCD anyways.

You could do all this with a BASIC stamp development board if you don't want to implement a BASIC stamp yourself.

 

[Sceadwian]

If you have the stamp use it, but I would not recommend continuing to use them. If you complete a few projects using them you might want to upgrade to using PIC's or AVR's and learning a little more about their function.

 

[Revolvr]

For temp sensing you could go with a pre-calibrated IC like the LM34 series. If using thermistors, these drop resistance as temp increases but are non-linear so they need calibration. Calibration is a simple log function - look up "Steinhart-Hart" equations for info.

-- Dan

 

[Nigel Goodwin]

If using thermistors, these drop resistance as temp increases but are non-linear so they need calibration.

Depends on the type of thermistor, you get both negative and positive temperature coefficient ones!. Generally for calibration a lookup table is the best idea, as most thermistors don't follow a true log scale.

 

[micro1]

Thanks for the info. I think I may be way over my head here by looking at Nigel's infromation.
The airstreams (I guess we can call them A and B) will range in temp. from about 20 degrees F to 100 degrees F.

The distance or the thermistors from the controller will not exceed 10' and typically won't exceed 6'.

Is there a person or company who has the ability and desire to put together a project like this? I would like to talk to an expert and get a price before I spend 1-2 years of my life trying to learn to do this. Thanks - Micro1

 

[Nigel Goodwin]

You should be able to find plenty of STAMP examples for reading temperature, either using thermistors, or IC sensors.

 

[stevez]

Mixed air control is very common in the HVAC industry. Unless you really want to make your own I'd say you are better off purchasing the appropriate electronics - will likely already be pre-programmed.

 

[Russlk]

Are you trying to maintain the mixed air temperature constant? If so, that is a simple servo problem and all that is needed at the input air streams are thermometers. If the mixed air temperature is to vary according to the relation of the input streams, that is a complex problem and you need to specify the relations.

What is the voltage and current requirements of the motor?

 

[stevez]

Look at this:

http://www.honeywellbv.nl/uploads/files/MicroniK_brochure_(EN).PDF

This can be a very challenging problem however for most applications, relatively crude control is sufficient.

 

[micro1]

Steve and Nigel, thank you for the replies. The application for this device is indeed for the HVAC industry. My profession is a dicipline in that industry.
The control you link to, Steve, is a very common control in the industry, you will see it uses an economizer feature. Ironically this is much more complicated than what I want to build as it calculates enthalpy (moisture in the air) and air temperature, and determines if unconditioned outside air is appropriate to use for cooling in place of the primary (or secondary) refrigerant through a coil. Thus saving energy.
And although similar in nature, it is not what I need, nor would it be easier to modify than just building the control I need. I am very busy with my own profession, and of course have some other side projects as well, but I decided this was the year I would get this project done, so if I can't find a company to build one, I guess I'll have to try it myself.

 

[micro1]

Are you trying to maintain the mixed air temperature constant? If so, that is a simple servo problem and all that is needed at the input air streams are thermometers. If the mixed air temperature is to vary according to the relation of the input streams, that is a complex problem and you need to specify the relations.

What is the voltage and current requirements of the motor?

Not trying to maintain the mixed air temp. The mixed air temp is just a number in an equation (as are all the temps) that the micro will be programmed with to maintain a percentage of air in "STREAM A" relative to the total air of both "STREAM A" and "STREAM B"

The motor is determined by the size of the damper it must control. Voltage shall be 24 volts.

 

[stevez]

Micro - I may not have been clear. The link I provided points to one of many ready made controllers. The one I selected was overkill. My guess is that simpler devices are available. I do know of several people that I'd contact locally. They distribute controls for the HVAC and related industries. IM me and I'll pass along the manufacturer's names. What these guys have done for me before is take one of their standard control boards and drop in software that's been used over and over. It's what I'll call commercial grade stuff - not industrial grade. It's reliable but not bulletproof and the price tag is reasonable.