Introduction Construction-1 construction-2 construction-3 Calibration


As a reference you may wish to open up a new window to view the circuit while checking the list.

Parts List

        
RESISTANCES (all 1/4 W )                                                                            
 R1              10 meg 1%  ( or measured )
 R2              1 meg  1%        . .                                                                                        
 R3              100K   1%        . .                                       
 R4              1K     1%        . .                                                                                           
 R5 R6           10K to 47K (see text )   10%                                                                  
 R7 to R13       390 ohms                 10%                                                                                          
 R14 to R16      1K                       10%                                                                        
 RV1 to RV3      7K ( total resistance , see text )  
                                                                                             
CAPACITORS
 C1              .001 uF 5%
 C2              .01 uF  5%
 C3              .1 uF   5%            
 C4              1.uF Tantalum          
 C5,C6,C7        .001 uF Polyester
Filter capacitors .1 Poly. ( ICs by-pass )                                                                    
Filter Capacitor  200 uF/15V  (supply )
ICs IC1 CMOS, MC14553 , 3-Digit BCD Counter IC2 CMOS, MC or CD 14543 , BCD-to-7-Segment Latch/Decoder/Driver IC3 CMOS, MC or CD 4049 , HEX Inverting Buffer IC4 CMOS, MC or CD 4011 , Quad 2-Input NAND Gate . IC4 * A 4093 Schmitt trigger can be used and is direct substitute for the 4011
Transistors Q1 to Q3 2N2907 or similar PNP
Others Sockets 16 pins,3 ea 14 pins,1 ea Display 3 ea Common Anode LED display of your choice Switches 1 ea ,3- poles 4-positions Rotary switch 1 ea ,1-pole 1-position miniature toggle or slide switch ( for ON/OFF ) For Benchwork model Switch knob , case, Display red filter, Capacitor test socket or short lead wire with clips , battery holder .
Optional VR Voltage Regulator 780x (1.5 A TO220 ) positive voltage as required (optional) Bridge Rectifier bridge 50V/1A ( optional) Switch One small normally open push button switch ( Supply ON/OFF and Test ) For use with battery supply Socket 14 pin dip for 7 display current resistors

Construction

Notes
This project may be not suitable for the beginners as a certain amount of experience is required to achieve a good operating system , nevertheless the following construction suggestions should help everyone in preventing unwanted problems .
Unless you never make mistakes use sockets for all the ICs.
Keep all leads especially capacitor leads as short a physically possible.
Do not use ceramic capacitors as they are temperature sensitive and will be unstable and produce noise.
Best operating voltage is between 9 volts and 12 volts. Operation down to 6 volts is possible but with loss of sensitivity in the picofarad range. Display current limiting resistors values R7 to R13 will need to be adjusted to control brightness level below 10mA per segment . I used a 14 pins IC socket for R7 to R13 for quick adjustments . No need to mess up the PC board .
If and external power supply is used AC or DC install a regulator as well as a large filtering capacitor (200 uF) for stability.
If you decide to use a battery pack as your source of supply consider using a normally open push button switch in the supply line to prolong batteries life.
The rotary switch must be installed as close as possible to the capacitors , excessive long leads will result in a noisy system and unstable display.
The following will produce noise ; bad capacitors , poor wiring, cold solder , twisted wiring , bad connections , noisy supply lines , dirty switch contacts .

Introduction Construction-1 construction-2 construction-3 Calibration