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Here is my attempt of a digital volt meter (DVM) with auto ranging functionality. Note how the decimal point moves on the 7-segment displays when switching scales! It can measure from 0.1V up to almost 100V. The [1 to 1] scale has an accuracy of about 100mV, and the [10 to 1] scale has an accuracy of about 1V.
INSTRUCTIONS:
The voltage source on the left is the unknown. The 7-segment displays in the right show the result. Please allow time for the counters to increment to the correct amount (especially after changing scales). The current setup reads 24V.
GENERAL:
This is a ramp type DVM. So the right side is identical to my ramp type DVM example I made before (check that out in the DVM Series). A voltage divider on the left creates two different scales. A relay switches between scales. A schmitt trigger activates the relay when the unknown voltage goes outside the current scale.
Blue waveform: Unknown input voltage
Green waveform: Scaled input voltage
Orange waveform: Ramp voltage
Red waveform: Scale selection signal
DVM Series:
Ramp Type https://everycircuit.com/circuit/4592385207304192
Dual Slope Integrating Type https://everycircuit.com/circuit/6675184624599040
Integrator Type (voltage to frequency) https://everycircuit.com/circuit/6172260362354688
Successive Approximation Type (hex) https://everycircuit.com/circuit/6044286526947328
Successive Approximation Type (decimal)
https://everycircuit.com/circuit/5334865438048256
Ramp Type (negative volts) https://everycircuit.com/circuit/5763215168110592
Counter Type ADC https://everycircuit.com/circuit/4509930926899200
Tracking Type ADC https://everycircuit.com/circuit/6418942605918208
Tracking Type ADC Full Version https://everycircuit.com/circuit/4688147021299712
Flash Type ADC https://everycircuit.com/circuit/4806466994962432
Pipeline Type ADC https://everycircuit.com/circuit/5739735974412288
Pipeline Type ADC 2 Bit Stages
https://everycircuit.com/circuit/6081127019970560
DETAILS:
The resistive voltage divider reduces the unknown input voltage by a factor of 10.
Vout = Vin × R2 / (R1+R2)
In this case: R1 = 9k, R2 = 1k, Vout = Vin / 10.
The voltages 0.1 - 10V are taken directly from the input voltage (creates the [1 to 1] scale). The voltages 10 - 100V are reduced by the divider down to 1 - 10V (creates the [10 to 1] scale). The relay connects the correct scale to the subtractor (middle opamp and resistors).
By default, the relay connects the higher scale to the subtractor to protect against over-voltage. A digital zero on the coil selects the [10 to 1] scale, and a digital one on the coil selects the [1 to 1] scale. The scale needs to change at the 10V point. To prevent instability at the switch point, a schmitt trigger adds hysteresis of 0.5V.
The lower opamp, resistors, and volt source form the inverting schmitt trigger to switch the relay. The upper threshold is 10V, and the lower threshold is 9.5V. Going above 10V sends a digital zero (selects the [10 to 1] scale). Going below 9.5V sends a digital one (selects the [1 to 1] scale). This is also what controls the decimal points on the 7-segment displays.
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