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. 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. 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)
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