Below is a picture of the first PID controller prototype which is built with a Microchip PIC16F876A microprocessor.
 

 
On the left you can see 5 LEDs, which are used for indicating the temperature.
The middle one is green, the next 2 are yellow and the outer 2 are red.

The idea is that when the middle green LED is lit, the temperature is correct +/- 0.5 °C.
In this way the operator can easily see when the temperature is correct for brewing.
 

 
The temperature sensor is a Dallas DS18B20 and is mounted directly on the water boiler tank as shown in the picture above (A). It is placed quite near where the fresh water comes in (B). The reason for this is to make the controller respond as quickly as possible to temperature changes in the boiler tank.

The sensor is fixed by aluminium tape. To achieve a good temperature conductivity, heat sink compound is applied between the sensor and the boiler tank wall.

Next, we will measure the results from this setup.