Need help with circuit design

[cbtumedic]

Allright, I am going to let ya'll know that i am new to all this electronics design stuff. I am trying to design a series of circuits that will allow me to switch a relay on and off based on a temperature reading from a K thermocoupler. I am trying to switch it on at 593 degrees centigrade. Also i would like to make this controller selectable so that i can actually select between 4 different temperature settings using a multipole switch. I could really use some assistance in this, i know i am going to need to use a flip flop IC of some sort, but i am very green and could use some help. Thanks a bunch in advance. Also i am looking to make it even more advanced once i figure out how to make it in the first place, in the future i would like it to switch off at a lower temperature than what it switched on at.

 

[neon]

The thermocouple will just give you millivolts output as temperature rises or falls. you will defenetly need not flip flop but comparators and a reference voltage to switch from. Simple enough let me point out that these circuitry must not see more then 40 degrees celsius or meltdown. Ho i forgot you will ned thermocouple conditioning to setup the level higher then millivolts like volts.

 

[cbtumedic]

Ok, thanks for the reply, is there any way you could give me some component numbers of what i may need to get started, as i said i am very wet behind the ears. The temperature issue isn't bad as this will be well isolated from any heat source. Also if it's not too big of a deal could you draw up a simple schematic to get me going in the right direction. Thanks a million. Travis

 

[neon]

well you see not all thermocouple material are the same you must search for the device that will work in that range. then tell and see what can we do for you

 

[amdNRA]

Check this one out: http://www.discovercircuits.com/PDF-FILES/TEMPRELAY1.pdf
Just make the needed changes in the 820K resistor and/or pot. Do notice there's 2 voltages; 5 ref and 12v supply. Recalibrate this for your application. Make sure to use a low ripple supply. Later, Gil.