Project # 05    
ICL7107 3 1/2 digit Panel Meter with 7-seg. Displays
(0 ~ 1.999V)
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Description

  • 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)


Resistors 
(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 --
100K
R 6 --
470K
R 7 -- 1M
R 8 --
10 Ω  *
R 9--  10K
    *
R10 --
470 Ω

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

Diode

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

W1 --- Multi turn precision trimmer pot
        5K 
(# 502)

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

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

Capacitors

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 ---
3
1/2 digit Panel Meter IC
              (# ICL7107)
  Datasheet (pdf)


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

CONSTRUCTION

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

Diodes

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. 

<STEP-3> 
  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)
20V
 
200V
 
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