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17 January 2009

Digital Km Step Measurement Devices


Parts of Component:

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 PST 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)

Description:

This schematic measure 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 lights after every 50 meters of walking. A beeper (excludable), signals each count unit, which occurs every two steps. A normal step is calculated to span approx. 78 centimeters, thus the LED signaling 50 meters lights after 64 steps or 32 mercury switch's operations, the display indicates 100 meters after 128 steps and so on. For low battery consumption the display lights only on request, pushing 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's degree was found good for this kind of device. In any case, the most critical thing to do is placement and sloping degree of the mercury switch inside the box.

The principle operation:

C1A & IC1B form a mono stable multi vibrator providing some degree of freedom from excessive bouncing of the mercury switch. Therefore a clean square pulse enters IC2 that divide by 64. Q2 lights the dot of D1 every 32 pulses counted by IC2. IC3 & IC4 divide by 10 each 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 mono stable count. Q1 drives the piezo sounder and SW2 let you disable the beep.



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