# how can i make low cost circuts

#### gaurang patel

Joined Dec 2, 2007
5
Hi every one
I am trying to make a controller that uses thermal conductivity humidity sensor to sense the humidity in the green house. I think I have all the aspect on the things i need to use but, my problem is I dont know where to start. If one of the member would like to make some money to help me please sand a massage. please remember I am look for some one to explain and teach me how to make the controller not just make any old kind that I can buy out side in the market. Or If any one can let me know where I can find the right help.

#### Papabravo

Joined Feb 24, 2006
14,664
This is a puzzling request. On the one hand it is well known that a purchased component, if it exists, will cost far less then anything that can be designed and built by an amateur. The risk is also lower. When you embark on a design project there is always a chance that it will fail completely.

Assuming all that is irrelevant and you wish to embark on a design, the very first thing you must do is document your requirements. This is your chance to define what DONE means. If you can't do this then no amount of help is going to overcome this obstacle. You and anybody helping you will chase your tails around the palm tree like Sambo and the tiger.

Having this document will maximize your chances that anyone who decides to help you will have a clear picture of what you have in mind.

#### HarveyH42

Joined Jul 22, 2007
426
Being for a greenhouse, guessing your plants might certain requirements. Kind of depends what you need, and what you are willing to do. You left this to broad to begin. Need to better define the problem, what you need to correct it.

Some greenhouses regulate heat and humidity by opening vents and turning on fans to reduce. Some areas might need heaters or even humidifiers during some seasons.

Do you need a specific range? Do you just need to remove an excess? Do you need to suppliment? How much can you afford to spend? Size of the greenhouse? Is this a school project?

#### gaurang patel

Joined Dec 2, 2007
5
Papabravo , and HarveyH42 it is a simple humidity controller where the user can use potentiometers to set the humidity level, and the humidity sensor will scent the humidity in the air and if the humidity is too high then it will not do anything and if the humidity is lower then the set humidity then the relay will turn on. The relay will have 2 fan attached to it, and those will go on. I would like the circuit to be easy and low cost.
these knids of controller in the market cost $100 dollers, that is too much. is there a place i can buy a controller this type that cost around$20 to \$30 with out the outer housing.?

#### Papabravo

Joined Feb 24, 2006
14,664
I havn't checked prices lately but a Basic Stamp or a PICAXE should do the trick.

#### gaurang patel

Joined Dec 2, 2007
5

#### mrmeval

Joined Jun 30, 2006
833
They show you how in the data sheet. You have your microcontroller read the data from the memory chip which will store readings.

You probably want an older style humidity sensor that provides a low current switch closure that you can use to drive your relay.

A meter will tell you what the switch closure is on it, you provide voltage, 24v will do and relay which use 24v that controls contacts that turn on and off what you want.

http://appliances.pricegrabber.com/air-cleaners-heating-cooling-accessories/m/14346913/
http://www.longviewweb.com/h8908b-c.pdf