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# How to build Digital Step-Km Counter Circuit Schematic

2015-01-14 13:24
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## Description

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.

## Parts:

R1 = 22K 1/4W ResistorR2 = 2.2M 1/4W ResistorR3 = 22K 1/4W ResistorR4 = 1M 1/4W ResistorR5 = 4.7K 1/4W ResistorR6 = 47R 1/4W ResistorR7 = 4.7K 1/4W ResistorR8 = 4.7K 1/4W ResistorR9 = 1K 1/4W ResistorC1 = 47nF 63V Polyester CapacitorC2 = 100nF 63V Polyester CapacitorC3 = 10nF 63V Polyester CapacitorC4 = 10μF 25V Electrolytic CapacitorD1 = Common-cathode 7-segment LED mini-display (Hundreds meters)D2 = Common-cathode 7-segment LED mini-display (Kilometers)Q1 = BC327 45V 800mA PNP TransistorsQ2 = BC327 45V 800mA PNP TransistorsP1 = SPST Pushbutton (Reset)P2 = SPST Pushbutton (Display)IC1 = 4093 Quad 2 input Schmitt NAND Gate ICIC2 = 4024 7 stage ripple counter ICIC3 = 4026 Decade counter with decoded 7-segment display outputs ICIC4 = 4026 Decade counter with decoded 7-segment display outputs ICSW1 = SPST Mercury Switch, called also Tilt SwitchSW2 = SPST Slider Switch (Sound on-off)SW3 = SPST Slider Switch (Power on-off)BZ = Piezo sounderB1 = 3V Battery (2 AA 1.5V Cells in series)

## Circuit operation:

IC 1A & IC 1B form a monostable multi vibrator 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 disabling 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.