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08-04-2009

Digital Step-Km Counter

Max. range: 9,950 meters with two digits
Slip it in pants' pocket for walking and jogging

Circuit diagram:

Digital Step-Km Counter

Parts:

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

10nF   63V Polyester Capacitor

C4

10µF   25V Electrolytic Capacitor

   

D1

Common-cathode 7-segment LED mini-display
(Hundreds meters)

D2

Common-cathode 7-segment LED mini-display
(Kilometers)

   

IC1

4093   Quad 2 input Schmitt NAND Gate IC

IC2

4024   7 stage ripple counter IC

IC3,IC4

4026   Decade counter with decoded 7-segment
display outputs IC

   

Q1,Q2

BC327   45V 800mA PNP Transistors

   

P1

SPST Pushbutton (Reset)

P2

SPST Pushbutton (Display)

   

SW1

SPST Mercury Switch, called also Tilt Switch

SW2

SPST Slider Switch (Sound on-off)

SW3

SPST Slider Switch (Power on-off)

   

BZ

Piezo sounder

   

B1

3V Battery (2 AA 1.5V Cells in series)


Device purpose:

This circuit measures the distance covered during a walk. Hardware is located in a small box slipped in pants' pocket and the display is conceived in the following manner: the leftmost display D2 (the most significant digit) shows 0 to 9 Km. and its dot is always on to separate Km. from hm. The rightmost display D1 (the least significant digit) shows hundreds meters and its dot illuminates after every 50 meters of walking. A beeper (excludable), signals each count unit, occurring every two steps.
A normal step was calculated to span around 78 centimeters, thus the LED signaling 50 meters illuminates after 64 steps (or 32 operations of the mercury switch), the display indicates 100 meters after 128 steps and so on. For low battery consumption the display illuminates only on request, pushing on P2. Accidental reset of the counters is avoided because to reset the circuit both pushbuttons must be operated together.
Obviously, this is not a precision meter, but its approximation degree was found good for this kind of device. In any case, the most critical thing to do is the correct placement of the mercury switch inside of the box and the setting of its sloping degree.

Circuit operation:

IC1A & IC1B form a monostable multivibrator providing some degree of freedom from excessive bouncing of the mercury switch. Therefore a clean square pulse enters IC2 that divides by 64. Q2 drives the LED dot-segment of D1 every 32 pulses counted by IC2. Either IC3 & IC4 divide by 10 and drive the displays. P1 resets the counters and P2 enables the displays. IC1C generates an audio frequency square wave that is enabled for a short time at each monostable count. Q1 drives the piezo sounder and SW2 allows to disable the beep.

Notes:

  • Experiment with placement and sloping degree of mercury switch inside the box: this is very critical.
  • Try to obtain a pulse every two walking steps. Listening to the beeper is extremely useful during setup.
  • Trim R6 value to change beeper sound power.
  • Push P1 and P2 to reset.
  • This circuit is primarily intended for walking purposes. For jogging, further great care must be used with mercury switch placement to avoid undesired counts.
  • When the display is disabled current consumption is negligible, therefore SW3 can be omitted.

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