Water mixture control

[Tech_boy]

Hi guys,

I'm new to this forum, but I was told that you guys are willing to help in a short time.

I am currently doing a project. This involves in mixing hot and cold water to obtain a pre-defined temperature at the output, which will be set by the user. I am not going to use instant heating / cooling.

I will be using the 8051 microcontroller and LM35 temperature sensors.

1. I would like to know if any of you has done a similar project or knows from where I can find help.

2. I will be needing a valve which opens bit by bit to let the required amount of water to pass, however I can find any. It must be aple to keep in the required position (for example, only 2/5 of it is open etc) .. Preferable, it works with a stepper motor so that I can easily program it using the 8051 and C language. Do you guys know from where I can buy one please?

Thanks,
Tech_boy

 

[barry]

There are several approaches I can think of. There ARE electrically controlled valves available (just do an internet search of 'electrically controlled valves'!); these are not cheap, however. You could also use a stepper motor and connect it to a simple valve (i.e., a faucet). You didn't say where you're located, but in the US there's McMaster-Carr which stocks a lot of valves.

This sounds like it's also going to require some mechanical design, if you don't use an electrical valve, you'll some way of know when the valve is all the way closed or all the way open (limit switches, e.g.)

 

[Tech_boy]

I'm from Malta.. sry forgot to say so ..

The valves I found on the internet, which are electrically controlled, are more than 200Euro each, and I will be needing 2, and some do not meet my required specs to the full. Being a school project, I don't wish to spend so much.

I have got a 240V AC ball valve, however I was told by my examiner to avoid using it, 1. since I'm dealing with water and electricity, 2. to make use of steppers since I will be judged on my ability to use what we learned. Since I will be interfacing it with a microcontroller it is best to use a stepper motor in my opinion.


I also thought about the idea of connecting a stepper to a full-way T-valve. this valve only makes one turn and so I will program the stepper to make a 360 turn only and backward if required.
What do you think of such set-up?

Thanks a lot for your help

 

[kak111]

Are you familiar with the so-called. rc servo motors
I think the use one of these is maybe right choice in your project.

**broken link removed**

How RC servos work

Principles and overview of Servo Control for the hobbyist

Servo Database - RC Servo Specs and Reviews

 

[barry]

I think the stepmotor/valve solution sounds simple enough and steppers are a lot easier to interface than servos (you don't need any feedback/control loop). But I don't really have any experience with servos, so maybe they're not that difficult...

 

[kak111]

@barry

I wrote about RC-Servos
They have motor, motor driver , motor controller, position feedback and needed gearbox , all in one component

RC-Servo motors have three wire interface for controlling and power supplying.

Controlling of the servo motors is used using pulse controlling.
The control pulse is positive going pulse with length of 1 to 2 ms which is repeated about 50-60 times a second.

The controlling scheme is very easy to impelement with some electronics.
You can easily build a timer circuit using 555 timer chip for generating suitable controlling pulses
or you can use small microcontroller program to do that.

Movement 90...360 degrees , with small modification continous run.
Torque 1....40 kp/cm.... and over
Reasonable prices

Read attached links in post #4

KAK

 

[Tech_boy]

hey guys ..
thanks for your help,
sorry for the later reply but i was not notified about the answers.
I will be using vextra stepper motors attached to a quarter-turn valve.
In won't necessary need to know the exact position since the stepper will open or close depending of the feedback given from a temperature sensor attached at the ouput. howver in order to know the position if the valve is fully open or closed I will be using 2 micro-switches at each end.