| 摘要 |
<p>There is provided herein a microprocessor based circuit including a capacitor charging circuit incorporating, in a first configuration, a varying resistance (RS) to be measured. In a second configuration the varying resistance (RS) is switched out of the circuit. In either configuration the timing capacitor (CT) is allowed to charge until a microcomputer logic level is reached. During that charge interval a counter runs on the clock cycles to generate a digital representation of the interval and therefor of the RC constant. Operation of the circuit in the second configuration, absent the varying resistance, produces a 'zero' calibration for the circuit. Operation in the first configuration yields a representation of the varying resistance. Range sensitivity is accomplished by switching additional resistance (R1, R2...RN) into (or out of) the circuit to change the charging time of the capacitor.</p> |
