Project # 05    
ICL7107 3 1/2 digit Panel Meter with 7-seg. Displays
(0 ~ 1.999V)
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  • This DPM  (Digital Panel Meter)  accurately measures & displays DC voltage from 0 ~ 1.999V
  • DC power supply required is +5V (single supply)
  • Full-scale reading is 2V (or precisely 1.999V)
    (it can be easily modified to  extend the range to 20V or 200V)

Before you order : please note this project is intended for advanced hobbyists who have good electronics background and soldering skills & able to solve problems that they might encounter during construction of the project. Schematic is not available. Datasheets for the ICs used are provided (see Parts List)



PARTS LIST  (for 0 ~ 1.999 V)

(1 or 2%) 
Important : if you have problem reading the color code of precision resistors, please use a digital ohm meter to check & confirm the value of each resistor before insertion

R 1 -- 3 K
R 2 --
3 K  
R 3 -- 
39 Ω
R 4 --
470 Ω
R 5 --
R 6 --
R 7 -- 1M
R 8 --
10 Ω  *
R 9--  10K
R10 --
470 Ω

Q1  --- 2.5V precision Voltage reference IC (# TL431)
 Datasheet (pdf)


D1 -------- 1N4007 rectifier diode
D2 & D3 --  1N4148
switching diodes

W1 --- Multi turn precision trimmer pot
(# 502)

14-pin DIP IC socket
(for IC1)
40-pin DIP IC socket (for IC2)

PCB connectors -- 2-pin (2.54mm pitch)


C1 -- (not required)
C2 --
100pF ceramic cap (# 101 or 100p)
C3 --
0.1 uF mylar cap (# 100n or 104)
C4 --
4.7uF E.cap
C5 --
4.7uF E.cap
C6 -- 0.47uF (# 474 or 470n)
C7 -- 0.22uF (# 224 or 220n)
C8 --
0.01 uF (# 103 or 10n)
C9 --
0.1 uF ceramic cap (# 104 or 100n)    

Double side, FR4 printed circuit board included
IC1 --
 CMOS hex inverters (# 4069)  Datasheet (pdf)

IC2 ---
1/2 digit Panel Meter IC
              (# ICL7107)
  Datasheet (pdf)

Disp 1 & 2 -- 2 pcs of double, common anode 7-segment displays


Please follow closely the assembly procedure as stated below. The sequence of steps is very important & should not be changed. The project is constructed on a double-side PCB . Removing parts after soldering is very difficult ! Double-check the location & orientation of each component before soldering.
<STEP-1>  insert & solder the -> Resistors


ceramic & mylar capacitors

electrolytic capacitors

TL431 (Q1)

40-pin & 14-pin IC sockets (empty sockets without the ICs)

2-pin pcb connectors

Note : One end of the 40-pin IC socket has been intentionally cut to make soldering of the displays (in step2)  easier 
  <STEP-2>   Insert & solder the 2-digit, 7-segment LED displays ( 2 pcs)

Watch for the orientation of the displays
Please DO NOT insert the displays upside down !

<STEP-4>  Test &  Calibration
  1. Hook-up the test circuit (see diagram below) & calibration the DPM as shown.
  2. You will need :

    1) a stable 5V DC power supply to power up the DPM
    2) an accurate digital voltmeter (2V F/s)
    3) a 1.5V battery (any size) and
    4) a small screw driver for adjusting the DPM's trim pot

Note that the actual voltage of the battery is not important. It is merely used a temporary voltage reference for calibration purpose. Our objective is to tune the DMP so that it gives the same reading as the digital multimeter. 

  1. Insert the ICs to their respective sockets. 
    (ensure that the locations of pins # 1 are correctly identified)
  2. Set the correct decimal point for 2V full-scale by shorting (with solder) the 2 rightmost pads (see photo)
  3. Install the pcb on the plastic snap-in panel mounting cover & secure it with 4 screws 
  4. Insert the 2-pin wired connectors (2 sets) to the pcb & proceed to the calibration step



Modification for extending the measurement range

The original kit was designed for a full-scale reading of 2V (or 1.999V). You can easily modify the DPM to extend the range to 20V or 200V by changing the values of 2 resistors (see details below)
Full-scale -->> 2V
(original kit)
R8 10Ω 1M 1M
R9 10K 100K 10K
... other components values remain unchanged


Setting the correct decimal point

Calibration  : Use the same test circuit as above but a higher voltage reference is required. For 20V range, you may use a 12V battery as the voltage reference


Photo of a completed DPM