(a)[2]
State the purpose of the processing unit.
(b)[3]
A student is making a sensing unit to detect changes in temperature. The components available are a $4\,\text{V}$ supply, a fixed resistor with resistance $2.5\,\text{k}\Omega$ and a thermistor. The thermistor has a resistance of $3.0\,\text{k}\Omega$ at $6^{\circ}\text{C}$ and $1.8\,\text{k}\Omega$ at $20^{\circ}\text{C}$. Finish the circuit diagram in Fig. 9.2 to show how the resistor and thermistor should be arranged so that the output is above $2\,\text{V}$ at $6^{\circ}\text{C}$ and below $2\,\text{V}$ at $20^{\circ}\text{C}$. Label $V_{\text{OUT}}$ clearly.
(c)[2]
Suggest two applications of a relay in an output device.