Submit your Circuit
Thanks to all readers of EngineeringSlash,
We are giving an opportunity to all our readers to submit your circuits and circuit ideas and get them published under readers circuits along with your name . If you wish to send your cicuits mail to
lijogk@gmail.com
Include the following details :
1 .Circuit design
2. Description and any special notes
3. Your name
4. Qualification
5. A photo of you(if you wish to publish your photo)
Popularity: 13% [?]
Morning Alarm for babies
Here is a pleasant wake up alarm for the babies. As the morning light breaks in, the alarm gently wakes up the baby with a soothing musical note. What a pleasing way to make the baby rise to the day!
As already described, LDR has a very high resistance in darkness, which falls low as the light falls on it. Hence Ql does not conduct in darkness, as it is reverse biased by VR1. As the daylight breaks Ql goes into conduction and powers UM66 musical IC. Musical note at its output is amplified by Q2 and is fed into the 8-ohm speaker.
There a number of UM66 T chips, each giving a different note. You may also add a suitable voice COB like a sloka or a prayer in its place. The circuit is shown in Schematic 32.
You may use 3V with dry cells as the power supply, but operation at 3.6 V is good. It is better to use three or four Ni Cad or Ni Mh cells as they can be recharged and reused. Straight forward construction on a Vero board is all needed. Use plastic battery box available in the market to fix the batteries. Adjust 220k preset to the desired sensitivity, thereby at the required intensity of daylight, when the alarm should start singing.
Popularity: 20% [?]
Telephone Light
Telephone rings in the dead of the night and you grope in darkness for the light switch or may be for the cordless handset. Here is ingenious circuit which makes a light bulb glow whenever the telephone rings.
This is a good application where mains are triggered by triac by the action of an opto-coupler. The circuit is shown in Schematic 31.
Opto-coupler is device where the signal is coupled from input to the out put optically. It offers full isolation for both sides. Usually a LED is placed on one side internally and a photo transistor on the other, all housed in an opaque package similar to an IC. Unlike a transformer, opto coupler also allows DC linking. MCT2E opto coupler consists of an infrared LED (Pins 1, 2) driving a silicon phototransistor (Pins 4, 5, 6) in a 6 pin DIL package. Pinout details are given in Figure .
IR LED across pins 1 and 2 in MC2E opto-coupler is connected to the telephone line with a 47 k resistor. When the telephone rings, LED lights up internally. It is sensed by the phototransistor across pins 4,5 and 6. This drives the gate and the triac fires making the bulb glow.
You are warned that the circuit operates mains. There are only few components to be mounted. Check the pin-out of MCT2E and fix it properly. See that no arcing develops across the tracks or components. Use of optocoupler here, effectively isolates it from mains
Popularity: 26% [?]
Stitching Machine Motor Speed Control
Motor operated stitching machines have a series of carbon buttons in an enclosure operated by foot pedal. As the pressure on the foot pedal is increased or decreased by the foot, these buttons come close or move farther away, their resistance changes and hence the speed of the motor. Even though crude, it seemed to be okay, until my wife complained.
She said that the speed is little too fast even at the minimum pressure on the foot pedal, particularly for some repair work or at embroidery. Most of the housewives also like a little more control over speed of the machine. So here you have it.
The circuit is shown in Schematic 30. This is a standard triac speed control circuit much similar to domestic fan control circuit. Contrary to other triac circuits, you will find that an additional component known as diac is used in this circuit.
Triacsfire more symmetrically when used along with diac in AC power control applications. The diac is a bidirectional trigger diode which does not conduct (except for a small leakage current) until the break over voltage is reached. Its function is designed specifically to trigger a triac or SCR.
In the beginning triac Ql is not conducting; C1 is charged through variable resistor R3. This charge is coupled to Diac through R1, R3. When trigger level of the diac is reached (about 36 V), D1 fires and Triac TR1 is switched on. R3 and C1 combination sets the firing point of the triac from zero crossing along with Rl and R2. LI and C3 combination acts radio frequency filter for the radio interference caused by triac firing.
Entire circuit operates on mains. Care must be exercised when mounting components on normal Veroboard is risky. Remove alternate tracks and mount components. Triac should be mounted on a small heat sink as the triac tends to get hot particularly at lower speeds. All capacitors are polyester or polycarbonate rated at 600V or more. Rl is a preset for minimum speed control. Adjust this according to your requirement. R2 is the linear variable resistor like the volume control in the radios. Use the one with plastic shaft. L1 is a radio interference choke. Take 28 gage winding wire and make 10 turns on a 6 mm former. It can be wound on a round capacitor for C3 and even one end can be soldered to it also.
Popularity: 28% [?]
Electronic Lock
Here is an electronic code lock, which can be used as a door latch or key for ignition, etc. Operation is fairly tricky and there lies the beauty of the circuit. There are a number of switches, actually nine, which should be operated in a particular and owner – configured -sequence, or else the circuit will not drive the final SCR. The switches can of course be reconfigured as desired. SCR Output should be used with a suitable driver such as a solenoid for the door latch or a relay for the key.
The circuit is shown in Schematic 29. CD 4066 quad bilateral switch is made use of here. 12 V DC powers the circuit through SI. External switches S2—S9 are not connected in the same order as their number and that is part of the trick.
52 is a dummy switch, when pressed, LED D2 lights up only to fool the intruder. It is not connected to the rest of the circuit.
53 is the next switch. This operates internal switch 1 of CD 4066. When this switch is pushed, it pulls up trigger terminal (Pinl), and switch across 13 and 2 (SW1) is closed. It stays closed because of the feedback action of 3.3M resistance (Rl). Dl lights up indicating the closure of one switch in the sequence.
This powers the second internal switch (SW2) consisting of 5, 4, 3 pins. Power reaches Pin 5 and Pin 4 is the trigger terminal. When S5 switch is pushed on internal switch across 5 and 3 (SW2) closes. It charges CI capacitor 47uf through 100K resistance (R3). It can now feed the next switch as long as the capacitor can hold charge. CI is discharged through D3 and R5, which mean that next switch should be operated before this charge finishes.
To add to the confusion, the next switch is actually two switches in series comprising of S4 and S7 with trigger terminal at Pin 6. If they are pressed simultaneously, only if they are pressed simultaneously, internal switch across pins 8 and 9 (SW 3) closes. This charges 47uF capacitor (C2) through 100 k resistor (R6) which discharges through D4 and R7. Hence one has to press the next switch S8 before this charge is completed.
When S8 with trigger terminal at Pin 12 is operated in time, internal switch across pins 11 and 12 (SW4) closes.
SCR is fired now through R9. SCR drives a solenoid or a coil or any other drive mechanism of the lock. Final LED (D6) also lights up.
S9 is a blind switch only to fool the inadvertent user. S6 is another clever switch. This lights up LED D5 but also starts a piezo buzzer warning that somebody is fiddling with the lock. A 2200 uF capacitor charges and keeps the buzzer for some time. Use of capacitor is deliberate. It also makes the rogue user take a quick run.
Construction with CMOS IC is simple and straight. The trick here is to lay out the switches in a haphazard sequence, known only to the authorized user. Provision must also be made for easy change of code. With nine switches available, permutations are really many. Wiring must be carefully done to avoid false triggering.
Popularity: 35% [?]
Four Station Quiz
Here we have another Quiz circuit using a number of CMOS ICs. Now the number of contestants can be easily increased even though the present circuit shows only four. It uses a two input Quad AND gate (74HCT08), a four input Dual AND gate (74HCT21), a dual D flip flop (CD4013), and a 555. Truth tables of the ICs are given here. If any one of the four contestants presses the switch first, LED corresponding to his station lights up and the alarm goes on. All other switches will be immediately disabled. The. circuit has to be reset by a switch at the master to start the next question.
The circuit is shown in Schematic 28. It consists of four ICs. 74HCT08 has four AND gates with two inputs each. 74HCT21 has two AND gates each with four inputs, of which only one AND gate is used in this circuit. The other can be used for expanding the number of contestants. CD4013 dual D type flip flop and two such ICs are used in the present circuit. There is one inevitable 7555 used as an astable multivibrator for alarm.
There are four push button switches, one for each contestant. Each switch is connected to one input of AND gate of 74HCT08. This input is made low by IK resistance and can be pulled up by the push switch. All the other input gates are made common and connected to the output of 74 HCT21. Outputs of 74HCT08 are individually connected to the four set inputs of flip-flops in both CD4013s. Reset pins in CD4013 are made common, pulled down by IK resistance and connected to reset switch. This switch is used to reset the circuit for the next question.
Now Q outputs of CD4013 are made common through diodes Dl, D2, D3, and D4 and connected to the reset terminal of 7555. 7555 is wired as an astable multivibrator but its reset pin is pulled low by 3.3k resistor. Four LEDs D5, D6, D7, and D8 are connected at the Q outputs of CD 4013 to indicate which switch was pressed first, Q outputs are individually connected to the four inputs of one AND gate in 74HCT21.
Let us take the case of Si contestant. As soon as he presses the switch, if he does so first, the output of his AND gate (Ul A) goes high. This makes the SET pin of CD 4013 (U3A) high. Now output Q will be high and Q will be low. LED1 connected to Q will glow.
Now when Q goes high, it also brings this reset pin high through IN4148 diode and the alarm goes on. Now Q which is low is connected to an input gate of 74HCT21 (U2A) (It has four inputs). Out put of this IC is connected to all the second input gates of 7408. Hence they will ail be pulled low. Now even if any other switches are pressed, they will not respond. There is a provision for an LED at the individual station taken from Q output to show which station has responded first. So there two sets of LEDs, one set at the master and the other at individual contestants.
All the Q outputs of both CD 4013 are connected to the reset pin of IC7555 through individual diodes (IN4148). IN4148 diodes are fast recovery version, which look like small zener diodes. Hence when any one of the Q outputs becomes high, alarm will be activated at 7555. All the reset pins of CD4013 are connected to a switch (S5) which acts as a master switch. To normalize the operations, reset should be pressed by the master. Then the quiz can start all over again. The fastest will now get the priority and all others will be disabled.
74HCT08
Pinout and truth table are given in Figure 35 and Figure 36 respectively This IC has four AND gates with two inputs each in a single packing. As you can see from the truth table, output will be low if any or both of the inputs are low. Output goes high if only both inputs are high. It is an inverse of NAND gate already discussed.
74HCT21
Pinout and truth table are given in Figure 37 and Figure 38 respectively This IC has two AND gates with four inputs each in a single packing. As you can see from the truth table, output will be low if any or all of the inputs are low. Output goes high if only all the inputs are high.
CD4013
Now you have four ICs to deal with. Vero board will suffice, but think well for the best position of ICs so that a rninirnum number of interconnections are made. Switches must be rugged to stand the excitement of quiz competitions and should stand repetitive punches. You need to take three wires from the main console to individual contestant stations. One will be the power line and another is in the input line of AND gate, another is for the indication LED at the station. To save number of wires going to the stations this LED is given from the Q dashed output of the Flip-Flop. Power is regulated 5V, unless you can procure 74C versions of the ICs. Ground all unused inputs particularly of 74 HCT21.
Popularity: 30% [?]
1.5 Volt Tracking Transmitter
The current draw for this tracker is 3.7mA, so the 1.5V button cell will last awhile. What the heck am I suppose to hear you ask? When your circuit is working you should see the LED flash quite fast. Take your FM radio and search for the low-beat ‘humbe-humbe-humbe-etc’ equal to the flash of the LED (probably around the 100Mhz). Found it? If that position is interferering with a radio station you can fine-tune it with the variable capacitor. If you like to have the tracker around the 88Mhz you can do that by spreading the windings from the home-made coil just a bit (1/2 a millimeter or so). Anyways, play with it and learn. It is a nice project. The 12-inch antenna can be anything, it is not really that critical. I used a piece of 22 gauge flexible wire. I haven’t checked the range but will do that shortly.
* For stability, use a NPO types for C2 & C4.
* Resistance tolerance for R1 should be 1 or 2%.
* Frequency range is the usual 87-109Mhz on the FM dial.
* The coil is made from 22 ga ‘hookup’ wire, like the solid Bell phone wire. Leave the insulation on.
* The LED is the ‘High Brightness’ type for maximum illumination.
source electro-tech-online .com
Popularity: 26% [?]
3 FM transmitter circuits
Presenting 3 FM transmitter circuits .
Popularity: 25% [?]
Lie detector circuit
Here’s a simple lie detector that can be built in a few minutes, but can be incredibly useful when you want to know if someone is really telling you the truth. It is not as sophisticated as the ones the professionals use, but it works. It works by measuring skin resistance, which goes down when you lie.
Here are the details of the specific parts you will need
Part Total Qty. Description Substitutions
R1 1 33K 1/4W Resistor
R2 1 5K Pot
R3 1 1.5K 1/4W Resistor
C1 1 1uF 16V Electrolytic Capacitor
Q1 1 2N3565 NPN Transistor
M1 1 0-1 mA Analog Meter
MISC 1 Case, Wire, Electrodes (See Nots)
Notes
1. The electrodes can be alligator clips (although they can be painful), electrode pads (like the type they use in the hospital), or just wires and tape.
2. To use the circuit, attach the electrodes to the back of the subjects hand, about 1 inch apart. Then, adjust the meter for a reading of 0. Ask the questions. You know the subject is lying when the meter changes.
http://www.aaroncake.net/circuits/lie.htm
Popularity: 28% [?]
Simple Quiz Circuit with SCR
Here is a small and simple circuit to catch the first to punch the button in a quiz game. It is basically designed for two but can be expanded to accommodate more contestants. Present circuit works straightaway on mains but can be modified for use at low and less risky AC voltages also.
Silicon Controlled Rectifier (SCR) is much similar to a conventional rectifier except that the conduction is controlled by a gate signal. SCR does not normally conduct until a signal applied at the gate. Once it is turned on, it continues to be in the ON state even after removal of the gate signal, as long as a minimum holding current is maintained or removed. The symbol of SCR is given in Figure 34.
In a quiz game, we need to know, who pressed the switch first and a corresponding light bulb should glow indicating it or a buzzer should go on. Immediately all other switches should be disabled.
At the instance of power on, both SCRs will be in off state as both gates are at the ground level because of Rl and R2. Therefore, both the SCRs will not conduct, and both lamps will be off. Now let us say, if SI is pressed first, the gate of corresponding SCR1 is pulled up, SCR1 conducts and latches on. LI bulb glows and stays on because of SCR action. Now this SCR also makes diode Dl to conduct and pull down the gate of SCR2 disabling it. Hence it can not come on even if S2 is pulled up. Power up again to restart. Similar action is ensured when S2 is pressed. The circuit is shown in Schematic 27.
Popularity: 40% [?]