diagram ingram: step

Monday, July 8, 2013

Digital Step Km Counter

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 diagram:
digital_step_km_counter_circuit_diagram

Digital Step-Km Counter Circuit Diagram

Parts:
R1 = 22K 1/4W Resistor
R2 = 2.2M 1/4W Resistor
R3 = 22K 1/4W Resistor
R4 = 1M 1/4W Resistor
R5 = 4.7K 1/4W Resistor
R6 = 47R 1/4W Resistor
R7 = 4.7K 1/4W Resistor
R8 = 4.7K 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)
Q1 = BC327 45V 800mA PNP Transistors
Q2 = BC327 45V 800mA PNP Transistors
P1 = SPST Pushbutton (Reset)
P2 = SPST Pushbutton (Display)
IC1 = 4093 Quad 2 input Schmitt NAND Gate IC
IC2 = 4024 7 stage ripple counter IC
IC3 = 4026 Decade counter with decoded 7-segment display outputs IC
IC4 = 4026 Decade counter with decoded 7-segment display outputs IC
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)

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.

Streampowers

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Friday, March 29, 2013

Step Down Converter Controller

The TPS6420x controller is designed to operate from one to three series-connected cells or from a 3.3 V or 5 V supply obtained from a USB port. At its output it can produce 3.3 V at 2 A, suitable for powering a microcontroller-based system. With a suitable choice of external components (inductor, P-channel MOSFET and Schottky diode) the device can be operated over a wide range of possible output voltages and currents. A further advantage is its extremely low quiescent current consumption in power-down mode (100 nA typical) and in no-load operation (20 mA).

Also, if the input voltage is less than or equal to the desired output voltage, the device can connect the output directly to the input. Using just a few external components the TPS6420x can cover an output voltage range from 1.2 V up to the input voltage at up to 3 A, as long as a suitable P-channel MOSFET and Schottky diode are used. The device is an asynchronous step-down converter which, unlike the more widely-used PFM (pulse-frequency modulation) and PWM (pulse width modulation) types, involves a constant on-time and/or constant off-time.

Conventional controllers operate in PWM mode at medium to high loads, switching to PFM at lower loads in order to minimise switching losses. The controller described here also adjusts its switching frequency in accordance with the load to achieve a similar effect to the PFM/PWM controllers. The circuit diagram shows a classical step-down converter with an input voltage range from 3.3 V to 6 V and an output voltage of 3.3 V at a current of up to 2 A. The optional 33 m shunt resistor provides for current limiting.

Circuit diagram:

The TPS64202 offers a minimum on-time selectable between 1.6 ms, 0.8 ms, 0.4 ms and 0.2 ms and a fixed off-time of 300 ns. A MOSFET in the supply voltage path is switched on by the controller for as long as is necessary for the output voltage to reach its nominal value, or until the maximum permissible current, as determined by the shunt resistor, is reached. If the current does exceed this limit the MOSFET is switched off for 300 ns. If the nominal output voltage is reached, the MOSFET is switched off and remains in the off state until the output voltage once again falls below the nominal value.

At very low output currents the controller therefore operates in ‘discontinuous mode’ (DCM). Each switching cycle begins with the current at zero. It rises to the threshold or maximum value, and then falls again back to zero. At the moment of switch-off the Schottky diode causes the residual energy in the inductor to appear as a quickly-decaying oscillation at the resonant frequency of the output filter. This low-energy oscillation in discontinuous mode is normal and has no adverse effect on the efficiency of the converter.

It can be damped using the (optional) RC series network. At higher output currents the switch-down converter operates in continuous conduction mode (CCM). In this mode the inductor current never falls to zero. The output voltage is directly proportional to the switching mark-space ratio in this mode. If the Si2323 P-channel MOSFET from Vishay-Siliconix is not available, the IRLML6401 (12 V type) or IRLML6402 (20 V type) from IRF can be used instead.

Both these types have a higher on resistance, but do offer a lower gate capacitance. An alternative for the Schottky diode suggested is the MBRM140 (available from Digi-Key and Farnell), although this is in an SMB package rather than the Powermite package of the MBRM120. The voltage drop at 1 A is somewhat higher: 0.6 V instead of 0.45 V. The devices are manufactured by IRF and ON Semiconductor.

Literature at http://www.ti.com:
SOT23 Step-Down Controller, document reference number SLVS485
TPS6402 Evaluation Module (3.3 V, 2 A), document reference number SLVU093

Author: Dirk Gehrke

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