Battery Operated Auto Ranging DVMDrag Drop Image anywhere on Screen with Left Button - Zoom in or Zoom out with Scroll Wheel
This application note describes a technique for auto-ranging a battery operated DVM suitable for panel meter applications. Also, circuit ideas will be presented for conductance and resistance measurement, 9V battery and 5V supply operations, and current measurement.
Auto Ranging DVM with the ICL7106
The control signals necessary for auto-ranging are over-range, under-range, and clock. The over-range and under-range inputs control the direction of a scale shift, becoming active at the completion of an invalid conversion and remaining active until a valid conversion occurs. The clock input controls the timing of a scale shift. This signal should occur only once per conversion cycle, during a time window which will not upset an ongoing conversion and must be disabled after valid conversions.
The CD4029 is a four bit up/down counter, used as a register to hold the present state and as a counter to shift the scale as directed by the control inputs. The CD4028 is a BCD to decimal decoder interfacing the CD4029 and ladder switches. An additional exclusive OR gate package is added to drive the appropriate decimal point.