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Distance Counter

 
Measurements technics
9 years ago

Distance Counter


Presented here is a simple pedometer circuit. It measures the distance covered by you while walking. It may not work very well for running!

Circuit and working

Fig. 1 shows circuit diagram of the distance counter. The circuit is built around quad 2-input Schmitt trigger CD4093 (IC1), CMOS ripple carry binary counter/divider CD4024 (IC2), decade counter/divider CD4026 (IC3 and IC4), two transistors BC327 (T1, T2) and some other components.

Fig. 1: Circuit diagram of the distance counter

 

Gates N1 and N2 of IC1 form a monostable multivibrator that receives trigger input from tilt or mercury switch S1. When you lift your foot up and touch the ground back during walking, the mercury inside the switch makes a contact with its two metallic leads as shown in Fig. 2. This makes the current to flow between the metallic leads and a pulse is generated at pin 4 of IC1.

Open-close operation of mercury switch

Fig. 2: Open-close operation of mercury switch

 

Test Points

Test point

Details

TP0

GND, 0V

TP1

+3V when power switch S3 is closed

TP2

High when reset and remains high till 64 counts and low for the next 64 counts

TP3

Low to high when both S4 and S5 are pressed simultaneously

TP4

High when S5 is pressed to display the reading

This pulse is fed to pin 1 of IC2 that produces a divide-by-64 counter. Its output is given to inputs of gate N4 of IC1 and the output of N4 is fed to the base of transistor T2 through resistor R8. Transistor T2 drives the decimal point segment of common cathode 7-segment display (DIS1).

IC3 and IC4 are configured as decade counters to drive the 7-segment displays DIS1 and DIS2, respectively. Switch S4 resets these two counters and switch S5 enables DIS1 and DIS2 displays.

Transistor T1 drives the piezobuzzer (PZ1), which beeps after every two steps (one stride), provided switch S2 is closed. DIS1 and DIS2 displays indicate the distance covered in metre (m) and kilometre (km) units, respectively.

Generally, walking step of each individual is slightly different. Here, we assume that a single step is 78cm long, which is the average. According to this, 64 strides equal 100m (that is, 2×0.78×64=99.84m or 100m (approx.)) or 128 steps equal 100m.

DIS1 increments the digit after every 100m distance. That is, DIS1 displays 1 when distance covered is 100m and 2 when distance covered is 200m, and so on. After digit 9 in DIS1, DIS2 increments from 0 to 1 digit. The decimal point (dot) of DIS2 always glows to indicate separation of kilometre from the metre unit.

To save battery power consumption, DIS1 and DIS2 displays illuminate only when you push S5. If you want to reset the counter circuit, both switches S4 and S5 must be pressed simultaneously.

If you want to continuously illuminate DIS1 and DIS2 displays, remove switch S5 and connect the junction of S4 and emitter of transistor T2 to 3 V.

 

Parts List

Semiconductors :

IC1

- CD4093 quad 2-input NAND Schmitt trigger

IC2

- CD4024 counter/divider

IC3, IC4

- CD4026 decade counter/divider

T1, T2

- BC327 pnp transistor

Resistors (all 1/4-watt, ±5% carbon):

R1, R3

- 22-kilo-ohm

R2

- 2.2-mega-ohm

R4

- 1-mega-ohm

R5, R7, R8

- 4.7-kilo-ohm

R6

- 47-ohm

R9, R10

- 1-kilo-ohm

Capacitors:

C1

- 47nF ceramic disk

C2

- 330nF tantalum

C3

- 10nF ceramic disk

Miscellaneous:

DIS1, DIS2

- LTS543, 7-segment CC display

PZ1

- Piezo buzzer

S1

- Tilt/mercury switch

S2, S3

- On/off switch

S4, S5

- Tactile switch

CON1

- 2-pin terminal

- 3V battery

 

Construction and testing

An actual-size, single-side PCB for the distance counter is shown in Fig. 3 and its component layout in Fig. 4.

An actual-size, single-side PCB for the distance counter

Fig. 3: An actual-size, single-side PCB for the distance counter

 

Component layout for the PCB

Fig. 4: Component layout for the PCB

 

Mount DIS1 to the right of DIS2 as shown in the PCB so that you get proper readings. For example, if DIS2 shows 5 and DIS1 shows 2, the reading will be 5km and 200m. It means the distance travelled is 5200m.

After assembling the circuit on PCB, enclose it in a suitable plastic case so that you can keep it in your trouser's pocket or attach it to your belt.

Use 2-pin connector CON1 for 3 V battery in the PCB. Also fix switches S2 through S5 on the front side of the case.

The author is an electronics hobbyist.

Author: Yogesh Shukla

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