Panel meter using ICL7107 ICL7106

A very simple digital panel meter electronic project can be designed using the ICL7107 or ICL7106 high performance, low power, 3 1/2 digit A/D converters . The ICL7106 converter can drive LCD display and the ICL7107 converter can drive LED display .
The ICL7107 IC is that because it is powered by +5V and -5V it can accept inputs in the range +4V to - 4V.
As you can see from the schematic circuit most of the connections are between the ICL7107 and the LED's. The ICL7107 contains a number of inputs which can be varied to do different things. Of prime importance is the reference voltage, VREF, which is set by the 10K trimpot and R3. With the addition of only two capacitors the 7660 IC performs the complete supply voltage conversion from positive to negative for an input range of 1.5 to 10V, resulting in complementary output voltages of -1.5V to -10V.
ICL7107 uses a dual slope conversion technique. It relies on the charging and discharging of an integrating capacitor and having a counter count when the capacitor voltage is above a set value. Since the capacitor discharge is linear the counter reading is proportional to the input voltage.

A jumper selects the decimal point position in the displays .
Since the maximum value which can be displayed is 1999, voltmeters with full scale readings of 199.9mV, 1.999V, 19.99V etc. can be made.
The user must decide their own need. Then a reference voltage and maybe an input attenuator must be selected.
To use the meter to measure 0 - 199.9mV the trimpot is adjusted so that the reference voltage between pins 35 & 36 is 100mV. And to set the meter for 0 - 1.999V, VREF must be set to 1.0V.