This circuit was suggested by Analog devices (www.analog.com) in its Application Note AN-411 consisting of a circuit in which the output frequency varies directly with the acceleration applied to the sensor. This circuit is shown in figure 1. The supply can be done with single source voltages between 9 V and 12 V. The sensor is an ADXL05 of +/- 5g that converts any acceleration applied directly to a voltage. This voltage is then applied to an AD654 that consists of a low-cost voltage-frequency converter. The table next to the diagram gives the component values for different output frequency ranges. In this table we also have the breakdown of the acceleration in terms of Hertz / g. The output voltage on pin 8 of the ADXL05 is +2.5 V without acceleration and varies from 200 mV above or below this value for each 1g of acceleration detected. In the same diagram we have the formulas that allow the calculation of the components for obtain specific characteristics for the project. In the design, the resistors must be accurate and R1a must be approximately 50% of the R1b value. High precision resistors can be used for calibration and then switched to 1% tolerance types.
