IIST

SPEEDOMETER USING POWER FROM DYNAMO

Kosuru Sai Malleswar - Naveen Chander V. - Sahul M.P.V

To Build a dynamo-speedometer system that uses the power of a running bicycle to determine its speed.

Contents

Conceptual Design ............................................................................................................................. 2

Block Diagram ................................................................................................................................... 2

Power conversion circuit Schematic .............................................................................................. 3

Input Digitization ........................................................................................................................... 4

Pulse Counting Circuit ................................................................................................................... 5

Circuit to provide gating pulse to the counter circuit ................................................................ 5

Pulse counter and velocity display circuit ................................................................................. 6

Discussions………………………………………………………………………………………….9

Full circuit diagram…………………………………………………………………………….......10

Velocity measurement using Micro controller unit………………………………………………..10

Conclusion…………………………………………………………………………………………12

Conceptual Design:

Both, voltage and frequency of the dynamo output varies with the speed with which a

cyclist rides. The ac power from the dynamo can be rectified and regulated to produce a dc output

that can be used to power the circuitry .Meanwhile; the frequency of the sinusoidal wave can be

measured by the inbuilt circuitry. After this it just turns out to be a matter of calibration to get the

speed displayed on the screen. We have implemented the frequency measurement in the following

two ways:

1. Measurement using digital circuit and display the speed on Seven segment displays.

2. Measurement using Micro controller unit and display the speed on the LCD screen.

Block Diagram:

The entire speedometer can be summarized by the following block diagram:

1. The power obtained from rotation of the cycle tire is given to a dynamo, which converts

mechanical power into electrical power.

2. Assumption: The dynamo’s average output is AC voltage with average amplitude of 6V and

average power of 3W.

3. The dynamo’s output is converted into unregulated DC voltage using the full wave bridge

rectifier circuit.

4. Then the output is fed to the current driver circuit for current amplification such that the current

will be sufficient to charge the battery or drive the micro controller board.

Title

Size Document Number Rev

Date: Sheet of

<Doc> <Rev Code>

<Title>

A

1 1Wednesday , February 22, 2012

D1

D1N4007

D2

D1N4007

C1

1m

C2

22u

R1

47K

R2

15

D3

D1N4007

D4

D1N4007

D5

D1N4007

D6D1N4007

D7

D1N4007

D8

D1N5402

D9

D1N5402

U1

LM7805C

IN1

OUT2

GN

D3

Q1

BC177

D10D1N4007

LOADDYNAMO6Vac

0Vdc

0

BATTERY

5. The output of the current driver circuit is passed through regulator to get a constant DC output

of around 5V, which can be used to power up the microcontroller board.

6. When the voltage of the battery is more than the output of the regulator, the battery will supply

power to the micro controller.

7. When the output of the regulator is more than the voltage of the battery, the regulator’s output

will supply the power to the micro controller and the battery will be charging.

8. The output of the dynamo is digitized and fed to a pulse counting circuit, which can be used to

measure the frequency of the cycle rotation. This will be calibrated in a manner so as to show the

cycle speed at directly at the output.

The whole of the circuit can be broken down into 3 subheadings namely:

Power conversion

Input Digitization

Pulse counting

Power conversion circuit Schematic: This circuit generates 5V regulated DC output

voltage and also charges the battery.

o The output is supplied by the regulator LM7805 through D9 or by the battery through D8

diode. The output provider is who has the highest voltage to drive the output.

o D4-D5-D6-D7 is a bridge rectifier that converts the hub AC output to DC output. C1 filters

the rectified voltage.

o The D1, D2, R1, R2, Q1 and D3 are a 30mA constant current power supply used to charge

the battery. 30mA will be shared among micro controller and battery.

o The p-n-p transistor Q1 acts as a current amplifier in the circuit.

o R1 limits the current over D1 and D2 and polarizes the BC177 transistor (Q1).

o R2 defines the charging current.

o D3 avoids a battery current running back over Q1 'collector - base' and R1 when dynamo is

off.

o D5 makes a false ground to the regulator. It makes the regulator output be raised to

something near to 5.7volts. It was done to compensate the D6 dropout.

o D6 also avoids a current running back over regulator, discharging the battery when the

dynamo is off.

o C2 smoothens the output of the regulator.

o 4 Ni-cd rechargeable batteries can connected in series to provide the required power to the

micro controller when dynamo is off.

o They will recharge when the dynamo is on, sharing the current with the micro controller.

Input Digitization: This circuit produces the pulses required to measure the frequency from the

sine wave input. The output is of pulse form with magnitude either 0 or 5 volts.

Pulse Counting Circuit:

1. Circuit to provide gating pulse to the counter circuit:

The left IC555 in the figure is in Astable mode.

Ton = 0.7*(R1+R2)*C2 Toff= 0.7*R1*C2

The right side IC555 is in Monostable mode.

Ton=0.7*R3*C1

When the output of the astable flipflop is low, the output of the monstable does not change.

When the output of the astable flipflop goes low, it triggers monostable multivibrator.

Pulse width of monostable vibrator is 1.7 sec. T(off)= 0.1 sec.

The outputs of both the ICs and the output pulse signal from the comparator circuit are ANDed.

The number of pulses counted during the gating period (When the outputs of both the ICs are high)

,is the speed of the bicycle in Kmph.

At the end of the gating period, output of right side IC goes low and the compliment of it goes

high. So the rising edge of monostable vibrator’s output is used to enable D flipflops.

Title

Size Document Number Rev

Date: Sheet of

<Doc> <Rev Code>

<Title>

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1 1Wednesday , February 29, 2012

X1

555D

GN

D1

TRIGGER2

OUTPUT3

RESET4

CONTROL5

THRESHOLD6

DISCHARGE7

VC

C8X2

555D

GN

D1

TRIGGER2

OUTPUT3

RESET4

CONTROL5

THRESHOLD6

DISCHARGE7

VC

C8

C1

0.47uC2

10u

R1

1k

R2

47k

R3

1M

4.374V

4.372V

4.374V

C3

10n

C4

10n

0V

4.372V

4.132V

5.000V

0

V1

5Vdc

5.000V

R4

1kV V

2. Pulse counter and velocity display circuit

The above circuit takes square pulses as the input an displays the number of pulses which is

directly equal to the speed of the bicycle in Kmph.

WORKING:

Let ‘N’ be the number of pulses in time ‘t’ seconds and numerically equal to the number of

kilometres per hour (kmph). For a wheel circumference of 1.884 meter [diameter of 0.6 meter],

and number of pulses equal to 4 per revolution, we get the relationship:

Assume that the dynamo is of 8 poles.

(4 * N /t) pulses = N Kmph

= (N*4*1000)/(3600*1.884) meters per second = (N*1000*10)*(3600*1.88) pulses per second.

Therefore, we get time t in seconds ~= 1.70 sec.

At this instant, i.e. at t=1.7 sec., the number (speed) N will be latched corresponding to the ‘D’

flip-flops and displayed. At t=1.8 sec., output of astable flip-flop IC1(a) goes low and remains low

for 0.1 sec. This waveform is inverted and applied to the reset terminals of all counters (active

high). Thus the counters are reset and the previous speed is displayed. The new speed is displayed

at t = 1.7 +0.1 sec. In this way the speed will be updated every 1.8 sec.

This speedo meter can measure upto a speed of 99 kmph with 1 km resolution, which is more than

sufficient for a bicycle.

Discussions:

There is no unique way of designing a circuit and there is no circuit which is perfect in all

respects. Every circuit has its own pluses and minuses.

Pluses: The design uses frequency as the measuring parameter as opposed to the voltage since the

frequency of the dynamo output is equal to the frequency of rotation of the wheel (or its integral

multiple in case of a multi-pole dynamo). On the other hand, the dynamo voltage may or may not

be linear w.r.t the cycling speed. Added to this, practical difficulties arise during voltage

calibration, wherein the voltage might be attenuated by resistors, parasitic capacitors and diodes in

the circuit. The design is devoid of any sensors and external power supplies .The battery

(rechargeable) is maintained at zero charge initially to comply with the rules of the event. Keeping

a battery will be practical since, the circuit will not power off as the cyclist slows down after a

distance when he gets exhausted.

The design is implemented without using any microcontroller. Thus the programing is done at

hardware level, directly on logic gates and on the display. Also, the selection of the components

(resistors, capacitors and comparator IC’s) was a bit involved.

The power supply has an appreciable line regulation of 0.1 %. This is absolutely harmless for any

of the IC’s used.

Minuses: Design of the circuit is more or less complex. It could have been implemented

using a microcontroller in a much easier way.

Also, since hardware calibration is difficult and takes a lot of time and effort. (Proper pot

adjustment followed by choosing the capacitors for astable and monostable circuits).

The circuit is voluminous as such, and should be wired in a well-organized manner.

The comparator output is not a perfect square wave and results in wrong outputs many a time.

The circuit consumes a lot of power from the source since it has numerous active components as

opposed to the microcontroller wherein the microcontroller is the only load.

Circuit testing is highly time consuming.

Full circuit diagram:

VELOCITY MEASUREMENT USING MICRO CONTROLLER UNIT:

In this method, the output of the comparator is given to the digital input pin of micro controller i.e.

using the timer available and the interrupt routines, we can measure the frequency of the input,

which can be multiplied with two factors, one for the circumference of the bicycle wheel and

another for the number pulses generated by the dynamo per one rotation of the wheel. This number

of pulses depends on the number of poles of dynamo.

The code for measuring the frequency and displaying the speed:

#include <LiquidCrystal.h>

int pulseCount = 0;

LiquidCrystal lcd(12, 11, 5, 4, 3, 8);

void setup()

{

pinMode(2,INPUT);

lcd.begin(16, 2);

attachInterrupt(0, interrupt, RISING);

}

void interrupt()

{

pulseCount++;

}

void loop()

{

attachInterrupt(0, interrupt, RISING);

pulseCount = 0;

delay(1000);

detachInterrupt(0);

serviceLcd();

}

void serviceLcd()

{

lcd.print("Speed : ");

lcd.setCursor(0, 1);

lcd.print(pulseCount*2*3.14*0.3*0.001*3600/140);

//radius of the bicycle = 0.3m and dynamo has 4 poles

lcd.print(" kmph");

pulseCount=0;

}

Conclusion:

Finally, we designed a speedo meter with a resolution of 1 Kmph, which obtains the power by

converting the mechanical power delivered from cycling into regulated DC voltage, and measures

the velocity of the bicycle based on the concept of frequency measurement of pulse in the

following two ways:

1. Using a circuit made up of linear and digital ICs and displaying the speed on seven

segment display

2. Using the timer in the ATMEGA Micro controller unit and displaying the speed on the

LCD screen.