Output from UART chip to PWM circuit

Hi all,
I've this situation and i would really appreciate if anyone can help me.
I'm designing a temperature control of an oven for my degree course. There are 8-bit binary output from my UART chip, 3-bit is reserved control the wirewound resistors (heater) and the remaining 5-bit for the fan. While i'm doing some reserach on this area, i came across with PWM Controller and Darlington Pair circuits. I was thinking probably i can use this two circuits to control the heater and the fan.
In the PWM Controller circuit, it uses a potentiometer to give input signal to the fan, according to the textbook that i read. The speed of the fan will vary when we vary the signal of the potentiometer.So my question is how can i apply this circuit to do what i'm planning to do. Can anyone suggest me, please..
And, i guess if i have the ideas on how to to this, i can apply the theory to the Darlington pair circuit to control the heater.

The modern way to do this would be to use a small micro controller, such as Microchip PIC or Texas MSP430, Freescale HS8, etc, and use a built in UART and built in PWM output with some software to link the two.

Also Darlington pairs are very inefficient because they never have less than 1V across them when fully turned on. The modern way is to use a MOSFET with a low on resistance. You can get MOSFETS with built in ESD, thermal and over current protection so they are ideal for experimenting with. Look for one with a logic level gate threshold, that way you can wire it direct to an MCU with no other components.

Chris

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