Hello,
I need to create a small sized electronic circuit (Circuit=Ckt. here onward) , which can give 5 Jules of heat per 5 seconds with below constraints:
1. Ckt should use max. 6V DC input supply
2. No arduino, as it consumes space and it's costly
3. Size of the ckt. excluding battery should be as small as possible
4. Cost should be as less as possible
5. Output should be persistent or at least as per the calculations
6. Ready made heating elements can be used provided it is available easly

I have a very little knowledge in electronics... Please help me out with this..
Thanks in advance

 

You can use a resistor.
P=5 Jules/5 seconds=1W.
R=V^2/P=(6^2)/1W=36 Ohm
i=P/V=1W/6V=0.167A
A single two-watt resistor of 36 ohms is enough.
The resistor can be made of a high-resistance alloy. For example, from nichrome or the like.