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:  

Simple but reliable car battery tester

 This circuit uses the popular and easy to find LM3914 IC. This IC is very simple to drive, needs no voltage regulators (it has a built in voltage regulator) and can be powered from almost every source. This circuit is very easy to explain: When the test button is pressed, the Car battery voltage is feed into a high impedance voltage divider. His purpose is to divide 12V to 1,25V (or lower values to lower values). 

This solution is better than letting the internal voltage regulator set the 12V sample voltage to be feed into the internal voltage divider simply because it cannot regulate 12V when the voltage drops lower (linear regulators only step down). 

Simply wiring with no adjust, the regulator provides stable 1,25V which is fed into the precision internal resistor cascade to generate sample voltages for the internal comparators. Anyway the default setting let you to measure voltages between 8 and 12V but you can measure even from 0V to 12V setting the offset trimmer to 0 (but i think that under 9 volt your car would not start). 

There is a smoothing capacitor (4700uF 16V) it is used to adsorb EMF noise produced from the ignition coil if you are measuring the battery during the engine working.

 Diesel engines would not need it, but I'm not sure. If you like more a point graph rather than a bar graph simply disconnect pin 9 on the IC (MODE) from power. 

 The calculations are simple (default) For the first comparator the voltage is : 0,833 V corresponding to 8 V * * * * * voltage is : 0,875 V corresponding to 8,4 V for the last comparator the voltage is : 1,25 V corresponding to 12 V Have fun, learn and don't let you car battery discharge... ;-)

Long duration timer circuit

 Description. 

This timer circuit can be used to switch OFF a particular device after around 35 minutes. The circuit can be 

used to switch OFF devices like radio, TV, fan, pump etc after a preset time of 35 minutes. Such a circuit 

can surely save a lot of power. 

The circuit is based on quad 2 input CMOS IC 4011 (U1).The resistor R1 and capacitor C1 produces the 

required long time delay. When pushbutton switch S2 is pressed, capacitor C1 discharges and input of the 

four NAND gates are pulled to zero. The four shorted outputs of U1 go high and activate the transistor Q1 

to drive the relay. The appliance connected via the relay is switched ON. When S2 is released the C1 starts 

charging and when the voltage at its positive pin becomes equal to ½ the supply voltage the outputs of 

U1 becomes zero and the transistor is switched OFF. This makes the relay deactivated and the appliance 

connected via the relay is turned OFF. The timer can be made to stop when required by pressing switch S1.

Notes.

 • Assemble the circuit on a good quality PCB or common board. • The circuit can be powered from a 9V PP3 battery or 12V DC power supply. • The time delay can be varied by varying the values of C1&R1. • The push button switch S2 is for starting the timer and S1 for stopping the time. • The appliance can be connected via contacts N1 & N2 of the relay RL1. • The IC U1 is 2 input quad NAND gate 4011.  

Repeating Timer No.2

 Repeating Timer No.2   Description:   This circuit is based on a simple asymmetric oscillator. 

The length of time the relay remains energized -   and the length of time it remains de-energized -

 are set independently. With the component values shown   in the diagram - both periods are adjustable from about 1 to 30 minutes.    

Setting The Timer:   The frequency of the Astable Oscillator   depends on the value of C1 and the speed at which it charges and   discharges through the resistor network. The length of time the relay remains energized is controlled by   R2.And the length of the time it remains de-energized is controlled by R3. 

Owing to manufacturing tolerances - the precise length of the time periods available depends on the   characteristics of the actual components you've used. R1 & R4 set the minimum period lengths at about 1  minute - while R2 & R3 set the maximum periods at about 30-minutes. 

You can choose component values   that suit your own requirements. If your time periods don't need to be too precise - and more-or-less is   close enough - you can leave out the pots altogether - and simply rely on R1 & R4 to set the times.    421   Alternative Capacitor:  

 A regular electrolytic capacitor is polarised. If the charge on its plates is the wrong way round - DC current   will flow through the capacitor. If the current is high enough - the capacitor will heat up and explode.    When the oscillator is running - the polarity of the charge on C1 keeps reversing. So C1 needs to be non  polarised. However - you can simulate a non-polarised 470uF capacitor by connecting two 1000uF   

polarised capacitors back to back - as shown. How and why this works is explained in the Detailed Circuit   Description. Because non-polarised capacitors aren't widely available - the prototype was built using two   polarised capacitors.    Do not use the "on-board" relay to switch mains voltage. The board's layout does not offer sufficient   isolation between the relay contacts and the low-voltage components. If you want to switch mains voltage - mount a suitably rated relay somewhere safe - Away From The Board   you can use a multi-pole relay if you wish   

The timer is designed for a 12-volt power supply. However - it will work at anything from 5 to 15-volts. All you need do is select a relay to suit your supply voltage. The Cmos gates are being used as simple inverters. So - although I've used a Cmos 4093 in the circuit diagram - a Cmos 4001 or Cmos 4011 will work just as well

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VU Meter

 The Stereo VU Meter PC board with the components fitted. Only the battery and speaker are external, connected to flying leads. A close up of the completed unit. The overlay makes construction easy. Make sure the left-hand row of resistors starts with 47k at the bottom and 4k7 at the top. I saw one unit with the whole row reversed. It made very little difference to the performance of the unit, but it was not quite as sensitive as the correct version

The BOOTSTRAP circuit connects to the LED bar graph via A B C. Only one BOOTSTRAP circuit is provided on the board. It is capable of driving both bar graphs in a mono mode. For a stereo readout, you will need to build another bootstrap circuit. This will give a STEREO SOUND LEVEL INDICATOR.  

 

ROBOT-1 light-detecting circuits

 ROBOT-1 A simple robot can be made with 2 motors and two light-detecting circuits, (identical to the circuit above). The robot is attracted to light and when the light dependent resistor sees light its resistance decreases. This turns on the BC547 and also the BC557. The shaft of the motor has a rubber foot that contacts the ground and moves the robot. The two pots adjust the sensitivity of the LDRs. This kit is available from Velleman as kit number MK127.

PHONE TAPE

 PHONE TAPE - 2 The circuit is turned off when the phone line is 45v as the voltage divider made up of the 470k, 1M and 100k puts 3.5v on the base of the first BC557 transistor. If you are not able to get to cut the lead to the phone, the circuit above will record a conversation from an extension lead. The remote plug must be wired around the correct way for the motor to operate.

LED TORCH with 1.5v SUPPLY LED TORCH

 

LED TORCH with 1.5v SUPPLY This simple circuit will illuminate a super-bright white LED to full brightness with 28mA from a 1.5v cell. The LED is 20,000mcd (20cd @ 15° viewing angle) and has an output of approx 1lumen. The transformer is wound on a small ferrite slug 2.6mm dia and 6mm long. It is made from F29 ferrite material as the circuit operates at a high frequency (100kHz to 500kHz). The efficiency of the circuit revolves around the fact that a LED will produce a very high output when delivered pulses, but the overall current will be less than a steady DC current. BC 337 has a collector-emitter voltage of 45v. (BC338 has 25v collector-emitter voltage rating.) The voltage across the transistor is no more than 4v as the LED absorbs the spikes. Do not remove the LED as the spikes from the transformer will damage the transistor. The circuit will drive 1 or 2 while LEDs in series.