This circuitry measures the distance walked during a walk. The hardware is located in a small box placed in your pants pocket and the display is conceived as follows: The leftmost display D2 (the most significant digit) shows 0 to 9 km. and its point is always further to separate km. from hm. The rightmost display D1 (least significant digit) shows hundreds of meters and its point lights up after every 50 meters walk. The beeper (excluded) signals every unit count, repeating every two steps.
A normal step has been calculated to cover about 78 centimeters, so the LED signaling 50 meters lights up after 64 steps (or 32 mercury switch operations), the display shows 100 meters after 128 steps and so on. When the battery is low, the display lights up only when requested by pressing P2. Accidental resetting of the counters is ruled out because both buttons must work together to reset the circuit.
Obviously this is not a precision meter, but its degree of approximation has been found to be good for this type of device. In any case, the most important thing to do is to properly place the mercury switch inside the box and set its degree of tilt. IC1A and IC1B form a monostable multivibrator, providing some degree of freedom from excessive bounce of the mercury switch. Consequently, a pure square pulse is fed to IC2, which is divided by 64. Q2 controls the point segment of LED D1 every 32 pulses counted by IC2. Either IC3 and IC4 divide by 10 and control the displays.
P1 resets the counters and P2 turns on the displays. IC1C generates a rectangular audio frequency, which is switched on for a short time with each monostable count. Q1 turns on the piezo sounder and SW2 allows you to mute the beeper.
List of Electronic Components:
R1, R3 - 22K 1 / 4W Resistor
R2 - 2M2 1/4W resistor
R4 - 1M 1/4W resistor
R5, R7, R8 - 4K7 1/4W resistor
R6 - 47R 1/4W resistor
R9 - 1K 1/4W resistor
C1 - 47nF 63V polyester capacitor
C2 - 100nF 63V polyester capacitor
C3 - 10 nF 63V polyester capacitor
C4 - 10 uF 25V electrolytic capacitor
D1 - 7-segment mini LED display with common cathode (hundreds of meters)
D2 - 7-segment LED mini-display with a common cathode (kilometers)
IC1 - 4093 Quad 2 input circuit Schmitt NAND Gate IC
IC2 - 4024 7-step ripple counter IC
IC3, IC4 - 4026 Decimal counter with decoded 7-segment display outputs IC
Q1, Q2 - BC327 45V 800mA PNP transistors
P1 - SPST Button (Reset)
P2 - SPST Button (display)
SW1 - SPST Mercury Switch, also called Tilt Switch
Slide Switch SW2 - SPST (Sound On/Off)
Slider switch SW3 - SPST (power on/off)
BZ - piezo sounder
Battery B1 - 3 V (2 AA cells 1.5 V in series)