Electronica Stuff.blogspot.com: July 2012

Speed-Limit Alert

Tracking Devices

Galaxy 5:50 AM

Speed-limit Alert

Wireless portable unit

Adaptable with most internal combustion engine vehicles

Parts:

R1,R2,R19 1K 1/4W Resistors

R3-R6,R13,R17 100K 1/4W Resistors

R7,R15 1M 1/4W Resistors

R8 50K 1/2W Trimmer Cermet

R9 470R 1/4W Resistor

R10 470K 1/4W Resistor

R11 100K 1/2W Trimmer Cermet (see notes)

R12 220K 1/4W Resistor (see notes)

R14,R16 68K 1/4W Resistors

R18 22K 1/4W Resistor

R20 150R 1/4W Resistor (see notes)

C1,C7 100µF 25V Electrolytic Capacitors

C2,C3 330nF 63V Polyester Capacitors

C4-C6 4µ7 25V Electrolytic Capacitors

D1,D5 Red LEDs 3 or 5mm.

D2,D3 1N4148 75V 150mA Diodes

D4 BZX79C7V5 7.5V 500mW Zener Diode

IC1 CA3140 or TL061 Op-amp IC

IC2 4069 Hex Inverter IC

IC3 4098 or 4528 Dual Monostable Multivibrator IC

Q1,Q2 BC238 25V 100mA NPN Transistors

L1 10mH miniature Inductor (see notes)

BZ1 Piezo sounder (incorporating 3KHz oscillator)

SW1 SPST Slider Switch

B1 9V PP3 Battery (see notes)

Clip for PP3 Battery

Device purpose:

This circuit has been designed to alert the vehicle driver that he has reached the maximum fixed speed limit (i.e. in a motorway). It eliminates the necessity of looking at the tachometer and to be distracted from driving.

There is a strict relation between engine's RPM and vehicle speed, so this device controls RPM, starting to beep and flashing a LED once per second, when maximum fixed speed is reached.

Its outstanding feature lies in the fact that no connection is required from circuit to engine.

Circuit operation:

IC1 forms a differential amplifier for the electromagnetic pulses generated by the engine sparking-plugs, picked-up by sensor coil L1. IC2A further amplifies the pulses and IC2B to IC2F inverters provide clean pulse squaring. The monostable multivibrator IC3A is used as a frequency discriminator, its pin 6 going firmly high when speed limit (settled by R11) is reached. IC3B, the transistors and associate components provide timings for the signaling part, formed by LED D5 and piezo sounder BZ1. D3 introduces a small amount of hysteresis.

Notes:

D1 is necessary at set-up to monitor the sparking-plugs emission, thus permitting to find easily the best placement for the device on the dashboard or close to it. After the setting is done, D1 & R9 can be omitted or switched-off, with battery saving.

During the preceding operation R8 must be adjusted for better results. The best setting of this trimmer is usually obtained when its value lies between 10 and 20K.

You must do this first setting when the engine is on but the vehicle is stationary.

The final simplest setting can be made with the help of a second person. Drive the vehicle and reach the speed needed. The helper must adjust the trimmer R11 until the device operates the beeper and D5. Reducing car's speed the beep must stop.

L1 can be a 10mH small inductor usually sold in the form of a tiny rectangular plastic box. If you need an higher sensitivity you can build a special coil, winding 130 to 150 turns of 0.2 mm. enameled wire on a 5 cm. diameter former (e.g. a can). Extract the coil from the former and tape it with insulating tape making thus a stand-alone coil.

Circuit's current drawing is approx. 10mA. If you intend to use the car's 12V battery, you can connect the device to the lighter socket. In this case R20 must be 330R.

Depending on the engine's cylinders number, R11 can be unable to set the device properly. In some cases you must use R11=200K and R12=100K or less.

If you need to set-up the device on the bench, a sine or square wave variable generator is required.

To calculate the frequency relation to RPM in a four strokes engine you can use the following formula:

Hz= (Number of cylinders * RPM) / 120.

For a two strokes engine the formula is: Hz= (Number of cylinders * RPM) / 60.

Thus, for a car with a four strokes engine and four cylinders the resulting frequency @ 3000 RPM is 100Hz.

Temporarily disconnect C2 from IC1's pin 6. Connect the generator's output to C2 and Ground. Set the generator's frequency to i.e. 100Hz and regulate R11 until you hear the beeps and LED D5 flashes. Reducing the frequency to 99 or 98 Hz, beeping and flashing must stop.

This circuit is not suited to Diesel engines.

Soft Musical Telephone Ringer

Tele-phone

Galaxy 8:09 AM

Soft Musical Telephone Ringer

The normal telephone bell, at times (specially during night when one does not want to be disturbed), appears to be quite irritating. The circuit shown here converts the loud sounding bell into a soft and pleasing musical tone.

The incoming ring is detected by transistor T1 and components wired around it. In absence of ringing voltage, transistor T1 is cut off while transistor T2 is forward biased as resistor R2 is returned to the positive supply rails. As a result collector of transistor T2 is at near-ground potential and hence IC1 (UM66) is off. Also capacitor C2 is charged to a slightly positive potential.

During positive half of the ringing voltage, diode D1 forward biases transistor T1 and rapidly discharges capacitor C2 to near ground potential and cuts off transistor T2 which, in turn, causes IC1 to be forward biased and music signal is applied to base of transistor T3 which drives the speaker. During negative half of the ringing voltage, capacitor C2 cannot charge rapidly via resistor R2 and hence transistor T2 remains cut off during the ringing interval. Thus the soft musical note into the loudspeaker sounds in synchronism with the ringing signal. When handset is lifted off the cradle, the ringing voltage is no more available and hence the soft musical note switches off

Telephone amplifier

Tele-phone

Galaxy 8:03 AM

Telephone amplifier

While talking to a distant subscriber on telephone, quite often we feel frustrated when the voice of the distant subscriber is so faint that it is barely intelligible. To overcome the problem, circuit of an inexpensive amplifier is presented here. It can be assembled and tested easily. There is no extra power source needed to power up the circuit, as it draws power from the telephone line itself. The amplifier will provide fairly good volume for the telephone conversation to be properly heard in a living room. A volume control is included to adjust the volume as desired.

The circuit is built around IC LM386. Diodes D6 and D7 are used to limit the input signal strength. Transformer X1 is a transistor radio's output transformer used in reverse. Asoriginal secondary (output) winding is connected in series with the telephone lines, the speech signals passing through the lines cause change in the magnetic flux in the core of transformer and thereby induce signal voltage across the primary winding. This audio signal is used as input for IC LM386. Diodes D2 through D5 connected in bridge configuration constitute a polarity guard so that the amplifier is powered with correct polarity, irrespective of the line polarity, Zener diode D1 may have any breakdown voltage between 6 and 12 volts range. e.

There is no need of a separate power switch as the circuit energises (via the normally open contacts of the cradle switch) when one lifts the handset.

The circuit may be wired on a general-purpose PCB or by etching a PCB for this circuit.

The circuit can be easily tested by connecting a 6 volts supply to line terminals 1 and 2. A hissing sound will be heard from the loudspeaker. Now connect 6V AC from a transformer to terminals 1 and 2 and observe hum in the loudspeaker. The volume of the hum can be changed through potentiometer VR1. Diodes D6 and D7 limit the input below ± 700 mV.

The circuit is to be connected to the telephone lines in series with the telephone instrument, as shown in the figure

Dark-activated LED or Lamp Flasher

Sensor Powered

Galaxy 7:59 AM

Dark-activated LED or Lamp Flasher

Simple photo-sensitive circuit
3V battery supply

Parts:
R1 Photo resistor (any type)
R2 100K 1/2W Trimmer Cermet
R3,R4 10K 1/4W Resistors
R5 470R 1/4W Resistor
R6 47R 1/4W Resistor
C1 220µF 25V Electrolytic Capacitor
D1 1N4148 75V 150mA Diode
D2 LED Any type and color (See Notes)
Q1,Q2 BC337 45V 800mA NPN Transistors
SW1 SPST Switch
B1 3V (Two 1.5V AA or AAA cells in series, etc.)

Circuit operation:
This circuit adopts the rather unusual Bowes/White emitter coupled multivibrator circuit. The oscillation frequency is about 1Hz and is set by C1 value. The LED starts flashing when the photo resistor is scarcely illuminated. The onset of flashing can be set by trimming R2.

Notes:
Best results in flashing frequency can be obtained using for C1 a value in the 100 to 1000µF range.
To drive a filament lamp the following changes must be made:
Use a 2.2 to 3V, 250-300mA lamp in place of the LED
R2 = 10K 1/2W Trimmer Cermet
R3, R4 = 1K 1/4W Resistors
R6 = 1R 1/4W Resistor
C1 = 470 to 1000µF 25V Electrolytic Capacitor
In LED-mode operation the stand-by current consumption is less than 400µA.
In Lamp-mode operation the stand-by current consumption is about 3mA.

Touch Sense Door Alarm

Sensor Powered

Galaxy 7:53 AM

Touch Sense Door Alarm

Hangs up on the door-handle

Beeps when someone touches the door-handle from outside

Parts:

R1 1M 1/4W Resistor

R2 3K3 1 or 2W Resistor (See Notes)

R3 10K 1/2W Trimmer Cermet (See Notes)

R4 33K 1/4W Resistor

R5 150K 1/4W Resistor

R6 2K2 1/4W Resistor

R7 22K 1/4W Resistor

R8 4K7 1/4W Resistor

C1,C2 10nF 63V Ceramic or Polyester Capacitors

C3 10pF 63V Ceramic Capacitor

C4,C6 100nF 63V Ceramic or Polyester Capacitors

C5 2µ2 25V Electrolytic Capacitor

C7 100µF 25V Electrolytic Capacitor

D1,D2,D4 1N4148 75V 150mA Diodes

D3 5 or 3mm. Red LED

Q1,Q2,Q3,Q5 BC547 45V 100mA NPN Transistors

Q4 BC557 45V 100mA PNP Transistor

L1 (See Notes)

L2 10mH miniature Inductor

Hook (See Notes)

BZ1 Piezo sounder (incorporating 3KHz oscillator)

SW1,SW2 SPST miniature Slider Switches

B1 9V PP3 Battery

Clip for PP3 Battery

Device purpose:

This circuit emits a beep and/or illuminates a LED when someone touches the door-handle from outside. The alarm will sound until the circuit will be switched-off.

The entire circuit is enclosed in a small plastic or wooden box and should be hanged-up to the door-handle by means of a thick wire hook protruding from the top of the case.

A wide-range sensitivity control allows the use of the Door Alarm over a wide variety of door types, handles and locks. The device had proven reliable even when part of the lock comes in contact with the wall (bricks, stones, reinforced concrete), but doesn't work with all-metal doors.

The LED is very helpful at setup.

Circuit operation:

Q1 forms a free-running oscillator: its output bursts drive Q2 into saturation, so Q3 and the LED are off. When part of a human body comes in contact with a metal handle electrically connected to the wire hook, the body capacitance damps Q1 oscillations, Q2 biasing falls off and the transistor becomes non conducting. Therefore, current can flow into Q3 base and D3 illuminates. If SW1 is closed, a self-latching circuit formed by Q4 & Q5 is triggered and the beeper BZ1 is activated.

When the human body part leaves the handle, the LED switches-off but the beeper continues to sound, due to the self-latching behavior of Q4 & Q5. To stop the beeper action, the entire circuit must be switched-off opening SW2.

R3 is the sensitivity control, allowing to cope with a wide variety of door types, handles and locks.

Notes:

L1 is formed winding 20 to 30 turns of 0.4mm. diameter enameled copper wire on R2 body and soldering the coil ends to the resistor leads. You should fill R2 body completely with coil winding: the final turn's number can vary slightly, depending on different 1 or 2W resistor types actual length (mean dimensions for these components are 13-18mm. length and 5-6mm. diameter).

The hook is made from non-insulated wire 1 - 2mm. diameter (brass is well suited). Its length can vary from about 5 to 10cm. (not critical).

If the device is moved frequently to different doors, Trimmer R3 can be substituted by a common linear potentiometer fitted with outer knob for easy setup.

To setup the device hang-up the hook to the door-handle (with the door closed), open SW1 and switch-on the circuit. Adjust R3 until the LED illuminates, then turn slowly backwards the screwdriver (or the knob) until the LED is completely off. At this point, touching the door-handle with your hand the LED should illuminate, going off when the hand is withdrawn. Finally, close SW1 and the beeper will sound when the door-handle will be touched again, but won't stop until SW2 is opened.

In regular use, it is advisable to hang-up and power-on the device with SW1 open: when all is well settled, SW1 can be closed. This precautionary measure is necessary to avoid unwanted triggering of the beeper.