Track Your Distance Through a Bicycle Odometer

Just like cars that
measures the distance it can travel, you can also do it with your
bicycles. We usually keep track of our mileage to see how far our
strength can go but would it be of great use if we track it because we
are maintaining a workout everyday considering the calories we are

If you want to make your own odometer, you will need a micro controller that generates pulse and a MOSFET that converts those voltage pulses. Just remember to check your batteries all the time.
红包扫雷苹果下载地址 The best way of burning calories is to move those muscles everyday! Set your bikes and your odometer! Burn fats!

Cheap AC Current Measurement

The easy way to measure
high AC currents is to use a clamp meter but these are generally quite
expensive and cost several hundred dollars at a minimum. Add-on
clampmeter adaptors can work well but they only work with digital
multimeters which have millivolt AC resolution. This is because the
output of most clamp adaptors is quite low, 0.1A = 1mV, for example.
This is no good for typical cheap DMMs which
have a lowest AC voltage range of 200V. This circuit can be built into a
low cost clamp meter such as the Digitech QM-1565 from Jaycar
Electronics. When dismantling this clamp adaptor, remove the label which
has the AC range conversion factors and then undo the two screws gain
access to the inside.

Cheap AC Current Measurement Circuit

Cheap AC Current Measurement Circuit Diagram

The two cross-connected transistors act like low voltage drop diodes
to generate a DC voltage which is proportional to the current in the
primary of clamp adaptor (ie, the circuit under test). The recommended
transistors are power germanium types such as ADZ16, AD162, AD149,
ADY16, 2SD471, OC16 and OC28. This approach gives lowest voltage drop
and good linearity, from 10 to 300A. Schottky power diodes can also be
used but the result will not be as linear. To calibrate, wind 10 turns
through the clamp adaptor’s jaws and feed a current of 20A through the
winding. This is equivalent to a single turn carrying 200A. Set the
trimpot to suit your multimeter, normally set to the 2V DC range. Do not
calibrate for a low current otherwise accuracy at high currents will be

author: gerard la rooy – copyright: silicon chip electronics

Simple Stereo VU Meter

I like to see lights
move to music. This project will indicate the volume level of the audio
going to your speakers by lighting up LEDS. The LEDS
can be any color so mix them up and really make it look good. The input
of the circuit is connected to the speaker output of your audio
amplifier. You want to build two identical units to indicate both right
and left channels. The input signal level is adjusted by the 10k ohm VR.
If you wish to make a very large scale model of this unit and hang it
on your wall there is an optional output transistor that can drive many LEDS at once. The unit I built drove three LEDS for each output. The sequence of the LEDS lighting are as follows Pin 1, 18, 17, 16, 15, 14, 13, 12, 11, 10.


Circuit diagram

Check Inductors With This Simple Q Meter

While LCR
meters are readily available at reasonable cost, they do not measure
the Q of an inductor. This circuit enables you to measure the Q of
inductors with the aid of an RF signal generator. A capacitor is
connected in parallel with the inductor to form a tuned circuit. By
varying the frequency, you can measure the resonance frequency of the
tuned circuit and its -3dB bandwidth. The Q is then the resonance
frequency divided by the -3dB bandwidth. Transistor Q1 is an emitter
follower acting as input buffer to drive RF transformer T1. The
secondary winding of T1 then drives the parallel tuned circuit formed by
红包扫雷苹果下载地址 the inductor under test (Lx), T1’s secondary and tuning capacitor VC.

The tuned circuit so formed is buffered by JFET Q2 and transistor Q3 which form a cascode stage with about 3dB of gain. The JFET
provides a high impedance so that the loading of the tuned circuit is
minimal (note: an MPF102 can be substituted if you cannot obtain a
2N5485). The RF output from Q2’s collector can be monitored by an
oscilloscope to easily find the point of resonance and read the
frequency. Alternatively, the RF output can be read by an external
frequency meter. Diodes D1 & D2 and the 5.6nF capacitors form a
voltage doubler rectifier to drive a 100µA DC meter so that the
resonance can be found (in the absence of an oscilloscope).

Trimpot VR1 provides a sensitivity adjustment for the meter.
Transformer T1 is wound on a 12mm diameter ferrite toroid core. The
primary winding consists of 50 turns of 0.2mm diameter enamelled copper
wire, while the secondary is a single turn consisting of a strip of
brass 0.5mm thick and 2.5mm wide bent into a horseshoe shape and
threaded through the centre of the toroid. VC is a small AM tuning
红包扫雷苹果下载地址 capacitor with both gangs connected in parallel.

To measure Q, the output of the RF signal generator should be around
0.5V peak. Adjust the frequency until the meter’s reading peaks, then
adjust VR1 so that the meter reads full scale (100µA). Read the
resonance frequency F0 from the frequency scale of the signal generator
or better still, the reading on a frequency meter.

Next, increase the signal frequency until the meter reads 70µA and
note this frequency as F2. That done, reduce the frequency on the signal
generator below the resonance frequency until the meter again reads
红包扫雷苹果下载地址 70µA and note this frequency as F1. The Q can now be calculated as:

q = f0/(f2 – f1)

While using a variable tuning capacitor will enable a wider range of
inductors to be tested, the main advantage is estimating the
distributed capacitance of the inductor as well. To do this, you have to
calibrate the tuning scale with a capacitance meter, by measuring the
capacitance across the tuning capacitor with no inductor connected. This
is done with the unit switched off. Marking off increments of 20pF
should be sufficient.

Set the tuning capacitor to say ¼ of its maximum value and note this
value as C1. Adjust the RF signal generator frequency so that the
inductor under test is at resonance and note this frequency as F0. Now
set the RF generator frequency to half F0, adjust the tuning capacitor
until resonance and note this capacitance as C2. The distributed
capacitance of the inductor is (C2 – 4C1)/3.

Digital Bike Tachometer

This digital DIY
tachometer for bikes uses two reed switches to get the speed
information of the bicycle. The reed switches are installed near the rim
of the wheel where permanent magnets pass by. The permanent magnets are
attached to the wheelspokes and activate the reed switches everytime
they pass by it. The speed is digitally displayed.

The tachometer circuit works according to this principle; the pulses
created by the reed contacts are counted within a certain time
interval. The resulting count is then displayed and represents the speed
of the bike. Two 4026 ICs are used to count the pulses, decode the
counter and control two 7-segment LED display. RS flip-flops U3 and U4 function as anti-bounce.

Electronic bicycle DIY tachometer circuit diagram

The pulses arrive at the counter’s input through gate U7. The
measuring period is determined by monostable multivibrator U5/U6 and can
be adjusted through potentiometer P1 so that the tacho can be
红包扫雷苹果下载地址 calibrated. The circuit U1/U2 resets the counters.

Since batteries are used to power the circuit, it is not practical
to support the continuous display of speed information. This circuit is
not continuously active. The circuit is activated only after a button is
pressed. At least three permanent magnets must be installed on the
wheel. The circuit can be calibrated with the help of another
红包扫雷苹果下载地址 pre-calibrated tachometer.

Multimeter as Lightning Detector

Most digital multimeters
have a sensitivity of 200 mV and in input impedance of 10 MR. With this
information you can calculate that at full scale there will be a
current of 20 nA (nano-ampères). In reality you have a very sensitive
ammeter in your hand. Now that we know this, it becomes a mission to do
something with that knowledge. In other words, here is a solution that
requires a problem…

For example, try the following: Connect the ‘COM’ of the voltmeter
to ground (safety earth from a power point, central heating, plumbing,
etc.). Connect an old bicycle wheel spoke or a length of thin copper
wire to the ‘V’ socket so that you get a kind of antenna. When you place
this impressive looking apparatus on a windowsill during a thunderstorm
and set the meter to the 200 mV range, you will, with a bit of luck,
see nice deflections during lightning strikes. A nice thing is that you
will see a build-up of static charge long before the flash, and
immediately after the lightning flash the charge is gone.

Multimeter as Lightning Detector

Multimeter as Lightning Detector

Be aware of your own safety and those of others: Don’t walk out-side
with the thing or surreptitiously lead the ‘antenna’ to the outside.
This is really dangerous. In these modern times people still die from
lightning strikes! According to theory it is possible to improve the
lightning detector somewhat. A sharp point or edge collects more than a
rounded one. You probably have a razor blade somewhere. Attach this
razor blade at the top of the antenna. And again, be careful: keep
children and pets away. In the picture you can see an assembly were the
top of the antenna has one turn.

The razor blade is clamped in this and in addition it is a lot
harder to injure yourself this way. The ‘reception’ can be improved a
lot more by ionising the air in the region of the antenna with the aid
of radioactivity. Most of the mantles used in gas and petroleum lamps
contain a small amount of radioactive material and also smoke detectors
that work with an ionisation chamber are (lightly) radioactive. It is
better to leave the smoke detectors alone, because they often contain
very poisonous substances, but a piece of lamp mantle could be secured
to the razor blade with some two-component epoxy glue.

author: karel walraven – copyright: elektor electronics magazine

Speedometer For Model Cars

Avid model car fans are
naturally enough always interested in the technology and performance of
their cars. They would like to know as exactly as possible how fast
their model cars actually go, for example so that they can select the
final gear ratio for the best performance. Other factors can also be of
interest, such as the total distance that the car has travelled, since
it is worth knowing how long a car can run on one battery charge or one
tank of gas. There are impressive instruments available in the shops for
making these measurements, ranging all the way up to complete telemetry

However, they vary in price from expensive to frightfully expensive.
This is reason enough for model builders with modest budgets to look
for possible alternatives. The designer of the speedometer described
here has worked out such an alternative, and it is as simple as it is
inexpensive. He developed an adapter circuit that allows a perfectly
ordinary bicycle computer to be used as a speedometer. These devices
only cost around £10, and they have the advantage that they can display
not only the speed but also elapsed driving time, average speed and the
红包扫雷苹果下载地址 total distance travelled. It’s hard to imagine anything better.


Most likely everyone knows how a bicycle computer gets its speed
pulses. They are generated by a pickup that registers the rotations of
the front wheel. This pickup consists of two components. One of these is
a magnet that is clamped to a spoke, while the other is a magnetic reed
switch that is fixed to the front fork. The reed switch is connected by
a thin cable to the computer, which is mounted on the handlebars. Each
time the magnet passes the reed switch, it causes the switch contacts to
close, and the computer receives a count pulse.

This pickup cannot be used with a model car. Even if you could
somehow attach the magnet to a wheel, the wheel would then be so out of
balance that the car could not be driven. Some other kind of pickup is
thus needed. An optical sensor is an obvious solution. It is a
non-contacting and frictionless sensor, just like the magnet and reed
switch combination, but with the extra advantage that no additional
moving mass is required. The magnet is replaced in this case by a highly
reflective stripe on the side of the tyre, and the reed switch is
replaced by an infrared reflective sensor.

The most satisfactory solution for the reflective stripe turns out
to be white or silver-coloured paint. From practical experience, the
stripe should be around 1 cm wide, but in any case it should not be any
wider than one tenth of the width of the non-painted portion of the
tyre. The reflective sensor should naturally be mounted on the car in a
way that allows it to properly detect the difference between the
reflective and non-reflective areas of the tyre.


The only other thing that the new sensor needs is a circuit that
converts the signal from the reflective sensor into pulses that can be
used by the bicycle computer. There are two things that have to be done:
first, to convert optical pulses into sufficiently strong electrical
pulses, and second to adapt the frequency of the pulses. The first of
these points probably does not need any further explanation. The second
has to do with the difference between the circumference of a bicycle
红包扫雷苹果下载地址 wheel and that of a model car wheel.

Smaller wheels rotate faster for the same vehicle speed, so they
produce pulses at a higher rate. Although the circumference of the
bicycle wheel can be set in the computer, there are naturally limits to
the range of possible settings. It is not possible to deal with a wheel
diameter ratio of ten using the circumference setting alone. This means
that the number of pulses must be reduced by a suitable factor.


As can be seen in Figure 1, a relatively simple bit of electronics
can adequately realise the requirements just described. The heart of the
circuit is the reflective sensor (OPTO1). A Siemens SFH9201 IC is used
for this. It is available from Conrad Electronics, among other sources.
In the first version of the circuit, the LED
was simply driven by a DC current. This proved to be unsatisfactory,
since the sensor also reacted to ambient light. This produced so many
erroneous pulses that the accuracy of the speedometer suffered greatly.
We thus switched over to driving the LED with a 10-kHz AC current early on in the design.

This has the advantage that an AC amplifier can be used for the
detector circuit, which largely eliminates the effects of ambient light
variations. The 10 kHz signal for the LED is produced by the oscillator built around IC1a. Gate IC1b acts as a buffer that drives the sensor LED
via transistor T1. Whenever the white stripe on the tyre passes in
front of the sensor, the phototransistor in the sensor will briefly
conduct at a 10 kHz rate. A pulse train with a frequency of 10 kHz is
thus produced across resistor R4. This signal is coupled out by
capacitor C6 and then amplified by an AC amplifier formed by transistors
红包扫雷苹果下载地址 T3 and T4.

This results in a 10 kHz pulse waveform across resistor R15. This is
buffered by gate IC1c and then applied to a detector circuit consisting
of the diode D2, resistors R6 and R7 and capacitor C7. The job of the
detector circuit is to convert the short series of pulses into a logical
‘1’. The component values are rather critical, since capacitor C7
should be charged before the stripe has passed completely by the sensor,
but it should also be fully discharged via resistor R7 before the
stripe again appears in front of the sensor and a new pulse train
arrives. The output signal of the detector is buffered by gate IC1d and
finally ends up at the last part of the circuit, the divide-by-ten
counter IC2. This allows only every tenth pulse from the detector to be
passed on to transistor T2. The open collector of this transistor is
connected to the input of the bicycle computer.


The circuit runs with a supply voltage of 5 V. This can usually be
derived from the receiver module in the car. In the author ’s prototype,
a 6V supply voltage was available for the receiver. Capacitor C1
provides extra filtering for this voltage, which is then used directly
to supply the LED in the optocoupler (U+). The
supply voltage for the rest of the circuit is stabilised at around 5 V
by resistor R1 and the Zener diode D1. Capacitor C2 acts as a reservoir
红包扫雷苹果下载地址 capacitor, while C3 and C4 provide local decoupling for IC1 and IC2.


The circuit is not particularly critical, and given the small number
of components, it is also not difficult to build. The best way to build
it depends in part on the shape of the model car in question. The most
important factor is naturally that the sensor OPTO1 must have an
unobstructed view of the reflective stripe on the tyre. Since space is
always a consideration in model building, the author has designed a
printed circuit board for the speedometer that largely uses SMDs.
Figure 2 shows the track and component layouts of this board. Although
this board worked well in the prototype, we must emphasise that it has
not been tested in the Elektor Electronics lab.

It should thus be seen as a suggestion, in the sense of ‘this is a
possible solution.’ In addition to the exact construction of the adapter
circuit, the manner in which the bicycle computer itself is mounted
will naturally be largely determined by the specific features of the
model car in question. We leave this question to the inventiveness all
of those who build the speedometer circuit. Connecting the circuit is
dead easy. Wire the 6 V supply to the electrolytic capacitor C1 (with
the right polarity!), and connect the two leads of the computer cable to
resistor R10 and earth, respectively.

On the prototype board shown in Figure 2, the supply connections can
be made out with a bit of effort next to the labels TP1 and TP2, while
the output connections are labelled TP3 and TP4. Finally, there is one
last remark regarding setting the value of the wheel circumference in
the bicycle computer: don’t forget the factor of 10 provided by the
divider in the adapter circuit! For example, if the tire of the model
car has a circumference of 21cm, a circumference of 210 cm must be set
红包扫雷苹果下载地址 in the bicycle computer.

R1 = 220kΩ
R2 = 120kΩ
R3.R9 = 10kΩ
R4,R14,R15,R16 = 1kΩ
R5 = 33kΩ
R6 = 3kΩ9
R7 = 270kΩ
R8 = 100Ω
R10 = 470Ω
R11 = 8kΩ2
R12 = 180Ω
R13 = 1kΩ8

C1 = 100µF 16V
C2 = 100 µF 10V
C3,C4 = 100nF
C5 = 1nF
C6 = 10nF
C7 = 22nF
红包扫雷苹果下载地址 C8 = 1µF 10V

D1 = zener diode 5V6 1W3
D2 = 1N4148
T1,T2,T3 = BC547B
T4 = BC557B
IC1 = 74HC132SO
IC2 = 4017SO
OPTO1 = SFH9201 (Siemens)

Audio Power Meter

This simple circuit
indicates the amount of power that goes to a loudspeaker. The dual-color
LED shows green at an applied power level of
about 1 watt. At 1.5 watts it glows orange and above 3 watts it is
bright red. The circuit is connected in parallel with the loudspeaker
connections and is powered from the audio signal. The additional load
that this represents is 470 Ohm (R1//R3) will not be a problem for any
amplifier. During the positive half cycle of the output signal the green
LED in the dual-color LED will be turned on, provided the voltage is sufficiently high.

At higher output voltages, T1 (depending on the voltage divider R2/R1) will begin to conduct and the green LED will go out. During the negative half cycle the red LED
is driven via R3 and will turn on when the voltage is high enough. In
the transition region (where T1 conducts more and more and ‘throttles’
the green LED as a result) the combination of red/green gives the orange colour of the dual-LED. By choosing appropriate values for the resistors the power levels can be adjusted to suit.

Audio Power Meter Circuit

Audio Power Meter Circuit Diagram

The values selected here are for typical living room use. You will
be surprised at how loud you have to turn your amplifier up before you
get the LEDs to go! The resistors can be 0.25 W
types, provided the amplifier does not deliver more than 40 W
continuously. Above this power the transistor will not be that happy
either, so watch out for that too. Because T1 is used in saturation, the
gain (Hfe) is not at all important and any similar type can be used.
The power levels mentioned are valid for 4-Ohm speakers. For 8-Ohm
红包扫雷苹果下载地址 speakers all the resistor values have to be divided by two.

Photo Meter Assesses Ambient Light

Most PN-junction diodes
can be used as photodiodes. While not optimized for this application,
they do work. When the diode is reverse biased, it will produce a small
photovoltaic output as the light level is increased. LEDs
are particularly suited for this task because their housings are
transparent.You can construct a simple circuit that will assess the
condition of ambient lighting and, because many LEDs’ packages are
tinted to enhance their emitted color, may even yield a reasonable
红包扫雷苹果下载地址 evaluation of the detected color.

The results are not as effective as those obtained using a
high-quality optical filter, which typically has narrow bandpass
characteristics, but they can be quite acceptable.Though the design
described here does not produce the accuracy of designs with
laboratory-grade photodetectors and transimpedance amplifiers, it can be
quickly assembled and will produce usable results at a low cost.Three LEDs are used; experimentation will indicate which device has the best sensitivity to which color (Figure 1).

The ambient light falling on the LEDs causes some current flow—typically in the range of 10 to 100 nA—through each LED,
depending on the applied illumination level. This current flows through
the base of a transistor, Q1, and is amplified. Q1’s collector current
then splits between potentiometer R4, which acts as a first-stage gain
calibration, and the base of Q2.Q2 provides further amplification and
drives the left side of a bridge circuit (D1A and D1B). Note that R2/D1
and R3/D2 form a balanced bridge. Q2’s collector current provides a
slight imbalance to the bridge. The meter, M, measures this imbalance.
R5 adjusts the sensitivity of the meter.

Set R4 and R5 such that the meter has an appropriate deflection. R4
is useful for selecting the quiescent point; R5 is useful for adjusting
the sensitivity.Before building the circuit, check whether the LEDs can be used as photo sensors. To determine whether a given LED is a good photodiode, check the voltage across the LED
using a common digital multimeter set to its most sensitive
range—typically 200 mV. Typical output voltage should be approximately
红包扫雷苹果下载地址 0.3 to 1 mV with typical office illumination.

Meter Adaptor With Symmetrical Input

In contrast to an
ordinary voltmeter, the input of an oscilloscope generally has one side (GND)
connected to ground via the mains lead. In certain situations this can
be very problematic. When the measuring probe is connected to a circuit
that is also connected to ground, there is a chance that a short is
introduced in the circuit. That the circuit, and hence the measurement,
is affected by this is the least of your problems. If you were taking
measurements from high current or high voltage (valve equipment)
circuits, the out-come could be extremely dangerous! Fortunately it is
not too difficult to get round this problem.

All you have to do is make the input to the oscilloscope float with
respect to ground. The instrumentation amplifier shown here does that,
and functions as an attenuator as well. The AD621 from Analog Devices
amplifies the input by a factor of 10, and a switch at the input gives a
choice of 3 ranges. A ‘GND’ position has also been included, to
calibrate the zero setting of the oscilloscope. The maximum input
voltage at any setting may never exceed 600 VAC.
Make sure that R1 and R8 have a working voltage of at least 600 V. You
could use two equal resistors connected in series for these, since 300 V
红包扫雷苹果下载地址 types are more easily obtainable.

Circuit diagram:

Meter Adaptor Circuit

Meter Adaptor Circuit Diagram

You should also make sure that all resistors have a tolerance of 1%
or better. Other specifications for the AD621 are: with an amplification
of 10 times the CMRR is 110 dB and the
bandwidth is 800 kHz. If you can’t find the AD621 locally, the AD620 is a
good alternative. However, the bandwidth is then limited to about 120
kHz. The circuit can be housed inside a metal case with a mains supply,
but also works perfectly well when powered from two 9V batteries. The
current consumption is only a few milliamps. You could also increase R9
to 10 k to reduce the power consumption a bit more.

author: aart rombout – copyright: elektor july-august 2004