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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

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<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 !

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<STEP-4> Test & Calibration

Hook-up the test circuit (see diagram below) & calibration the DPM as shown.
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.

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<STEP-3>

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