This unit is meant to display average and peak vibration levels on machinery
bearings. It saves the highest of each in EEProm which the user can zero at
will.

The unit is made up of two parts. A remote sensor and a base unit. This is due
to space restrictions around the bearings and also to remove the main
electronics and display from the vibration. Over time the vibration could
damage the circuit and there's also a (greater) possibility of triboelectric
noise being introduced to the analog input.

The sensor output can reach +/-70V and has a high output impedance. In the
sensor box is a clamping setup to limit the output to +/- 3.7V (zener value +
diode voltage drop) and an opamp which provides both a low impedance output
and gain. Although the Sensor is capable if reading +/- 1400G, the useful
range for my application doesn't extend past 3G. The opamp gain will be set so
that the full range is +/- 4G (+/- 200mV).

Since the ADC's I have are all single-ended, the AC signal has to be converted
to positive DC. A second dual-opamp serves this purpose. It is used to supply
an offset voltage so that a 0G signal (0V) will be converted to +1.25V. In
this way a -4G (-200mV * sensor opamp gain) signal will be raised to 0V and a
+4G (+200mV * sensor opamp gain) signal will be raised to 2.5V. Firmware will
read the ADC and consider 1.25V as 0G.

More details as this unit gets breadboarded and built. No doubt I have errors
in the schematics and concepts that will need to be corrected 8)