General-Purpose Alarm Circuit Diagram

The alarm may be used for a variety of applications, such as frost monitor, room temperature monitor, and so on. In the quiescent state, the circuit draws a current of only a few microamperes, so that, in theory at least, a 9 V dry battery (PP3, 6AM6, MN1604, 6LR61) should last for up to ten years. Such a tiny current is not possible when ICs are used, and the circuit is therefore a discrete design. Every four seconds a measuring bridge, which actuates a Schmitt trigger, is switched on for 150 ms by a clock generator. In that period of 150 ms, the resistance of an NTC thermistor, R11, is compared with that of a fixed resistor. If the former is less than the latter, the alarm is set off.

When the circuit is switched on, capacitor C1 is not charged and transistors T1–T3 are off. After switch-on, C1 is charged gradually via R1, R7, and R8, until the base voltage of T1 exceeds the threshold bias. Transistor T1 then comes on and causes T2 and T3 to conduct also. Thereupon, C1 is charged via current source T1-T2-D1, until the current from the source becomes smaller than that flowing through R3 and T3 (about 3 µA). This results in T1 switching off, so that, owing to the coupling with C1, the entire circuit is disabled. Capacitor C1 is (almost) fully charged, so that the anode potential of D1 drops well below 0 V. Only when C1 is charged again can a new cycle begin.
Circuit Diagram:
It is obvious that the larger part of the current is used for charging C1. Gate IC1a functions as impedance inverter and feedback stage, and regularly switches on measurement bridge R9–R12-C2-P1 briefly. The bridge is terminated in a differential amplifier, which, in spite of the tiny current (and the consequent small transconductance of the transistors) provides a large amplification and, therefore, a high sensitivity. Resistors R13 and R15 provide through a kind of hysteresis a Schmitt trigger input for the differential amplifier, which results in unambiguous and fast measurement results. Capacitor C2 compensates for the capacitive effect of long cables between sensor and circuit and so prevents false alarms.
If the sensor (R11) is built in the same enclosure as the remainder of the circuit (as, for instance, in a room temperature monitor), C2 and R13 may be omitted. In that case,C3 willabsorb any interference signals and so prevent false alarms. To prevent any residual charge in C3 causing a false alarm when the bridge is in equilibrium, the capacitor is discharged rapidly via D2 when this happens. Gates IC1c and IC1d form an oscillator to drive the buzzer (an a.c. type). Owing to the very high impedance of the clock, an epoxy resin (not pertinax) board must be used for building the alarm. For the same reason, C1 should be a type with very low leakage current. If operation of the alarm is required when the resistance of R11 is higher than that of the fixed resistor, reverse the connections of the elements of the bridge and thus effectively the inverting and non-inverting inputs of the differential amplifier.
An NTC thermistor such as R11 has a resistance at –18 °C that is about ten times as high as that at room temperature. It is, therefore, advisable, if not a must, when precise operation is required, to consult the data sheet of the device or take a number of test readings. For the present circuit, the resistance at –18 °C must be 300–400 kΩ. The value of R12 should be the same. Preset P1 provides fine adjustment of the response threshold. Note that although the prototype uses an NTC thermistor, a different kind of sensor may also be used, provided its electrical specification is known and suits the present circuit.
Author: K. Syttkus
Copyright: Elektor Electronics
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Stepper Motor Controller Circuit Diagram

Stepper motors are available in several versions and sizes with a variety of operating voltages. The advantage of this general-purpose controller is that is can be used with a wide range of operating voltages, from approximately 5 V to 18 V. It can drive the motor with a peak voltage equal to half the supply voltage, so it can easily handle stepper motors designed for voltages between 2.5 V and 9 V. The circuit can also supply motor currents up to 3.5 A, which means it can be used to drive relatively large motors. The circuit is also short-circuit proof and has built-in over temperature protection. Two signals are required for driving a stepper motor. In logical terms, they constitute a Grey code, which means they are two square-wave signals with the same frequency but a constant phase difference of 90 degrees. IC1 generates a square-wave signal with a frequency that can be set using potentiometer P1.
This frequency determines the rpm of the stepper motor. The Grey code is generated by a decimal counter in the form of a 4017. Outputs Q0–Q9 of the counter go high in succession in response to the rising edges of the clock signal. The Grey code can be generated from the outputs by using two OR gates, which are formed here using two diodes and a resistor for each gate, to produce the I and Q signals. Here ‘I’ stands for ‘in-phase’ and ‘Q’ for ‘quadrature’, which means it has a 90-degree phase offset from the I signal. It is common practice to drive the windings of a stepper motor using a pair of push-pull circuits for each winding, which is called an ‘H bridge’.
That makes it possible to reverse the direction of the current through each winding, which is necessary for proper operation of a bipolar motor (one whose windings do not have centre taps). Of course, it can also be used to properly drive a unipolar motor (with centre-tapped windings). Instead of using a push-pull circuit of this sort, here we decided to use audio amplifier ICs (type TDA2030), even though that may sound a bit strange. In functional terms, the TDA2030 is actually a sort of power opamp. It has a difference amplifier at the input and a push-pull driver stage at the output.
Circuit diagram:
Stepper Motor Controller Circuit Diagram
IC3, IC4 and IC5 are all of this type (which is economically priced). Here IC3 and IC4 are wired as comparators. Their non-inverting inputs are driven by the previously mentioned I and Q signals, with the inverting inputs set to a potential equal to half the supply voltage. That potential is supplied by the third TDA2030. The outputs of IC3 and IC4 thus track their non-inverting inputs, and each of them drives one motor winding. The other ends of the windings are in turn connected to half the supply voltage, provided by IC5. As one end of each winding is connected to a square-wave signal that alternates between 0 V and a potential close to the supply voltage, while the other end is at half the supply voltage, a voltage equal to half the supply voltage is always applied to each winding, but it alternates in polarity according to the states of the I and Q signals.

That’s exactly what we want for driving a bipolar stepper motor. The rpm can be varied using potentiometer P1, but the actual speed is different for each type of motor because it depends on the number of steps per revolution. The motor used in the prototype advanced by approximately 9° per step, and its speed could be adjusted over a range of approximately 2 to 10 seconds per revolution. In principle, any desired speed can be obtained by adjusting the value of C1, as long as the motor can handle it. The adjustment range of P1 can be increased by reducing the value of resistor R5. The adjustment range is 1:(1000 + R5)/R5, where R5 is given in k.If a stepper motor is switched off by removing the supply voltage from the circuit, it’s possible for the motor to continue turning a certain amount due to its own inertia or the mechanical load on the motor (flywheel effect).

It’s also possible for the position of the motor to disagree with the states of the I and Q signals when power is first applied to the circuit. As a result, the motor can sometimes ‘get confused’ when starting up, with the result that it takes a step in the wrong direction before starting to move in direction defined by the drive signals. These effects can be avoided by adding the optional switch S1 and a 1-k resistor, which can then be used to start and stop the motor. When S1 is closed, the clock signal stops but IC2 retains its output levels at that moment, so the continuous currents through the motor windings magnetically ‘lock’ the rotor in position. The TDA2030 has internal over temperature protection, so the output current will be reduced automatically if the IC becomes too hot. For that reason, it is recommended to fit IC3, IC4 and IC5 to a heat sink (possibly a shared heat sink) when a relatively high-power motor is used. The tab of the TO220 case is electrically bonded to the negative supply voltage pin, so the ICs can be attached to a shared heat sink without using insulating washers.
Author: Gert Baars - Copyright: Elektor Electronics Magazine
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Mini Guitar/Bass Amplifier Circuit Diagram

Output power: 6W into 4 Ohm load, FET input stage - Passive Tone Control
Tiny, portable Guitar Amplifiers are useful for practice on the go and in bedroom/living room environment. Usually, they can be battery powered and feature a headphone output. This project is formed by an FET input circuitry, featuring a High/Low sensitivity switch, followed by a passive Tone Control circuit suitable to Guitar or Bass. After the Volume control, a 6W IC power amplifier follows, powered by a 12-14V dc external supply Adaptor or from batteries, and driving a 4 Ohm 10 or 13cm (4"/5") diameter car loudspeaker. Private listening by means of headphones is also possible.
Circuit diagram:
Mini Guitar Bass Amplifier Circuit Diagram
P1____________1M Linear Potentiometer
P2____________100K Log Potentiometer
R1____________68K 1/4W Resistor
R2____________470K 1/4W Resistor
R3____________2K7 1/4W Resistor
R4____________8K2 1/4W Resistor
R5____________680R 1/4W Resistor
R6____________220K 1/4W Resistor
R7____________39R 1/4W Resistor
R8____________2R2 1/4W Resistor
R9____________220R 1/4W Resistor
R10___________1R 1/4W Resistor
R11___________100R 1/2W Resistor
R12___________1K5 1/4W Resistor
C1____________100pF 63V Polystyrene or Ceramic Capacitor
C2,C5,C9,C14__100nF 63V Polyester Capacitors
C3____________100µF 25V Electrolytic Capacitor
C4____________47µF 25V Electrolytic Capacitor
C6____________4n7 63V Polyester Capacitor
C7____________470pF 63V Polystyrene or Ceramic Capacitor
C8____________2µ2 25V Electrolytic Capacitor
C10___________470µF 25V Electrolytic Capacitor
C11___________22nF 63V Polyester Capacitor
C12___________2200µF 25V Electrolytic Capacitor
C13___________1000µF 25V Electrolytic Capacitor
D1____________3mm red LED
Q1____________BF245 or 2N3819 General-purpose N-Channel FET
IC1____________TDA2003 10W Car Radio Audio Amplifier IC
SW1,SW2_______SPST toggle or slide Switches
J1_____________6.3mm Mono Jack socket
J2_____________6.3mm Stereo Jack socket (switched)
J3_____________Mini DC Power Socket
SPKR___________4 Ohm Car Loudspeaker 100 or 130mm diameter
  • Connect the output Plug of a 12 - 14V dc 500mA Power Supply Adaptor to J3
  • Please note that if the voltage supply will exceed 18V dc the IC will shut down automatically
Technical data:
Output power (1KHz sinewave):
6W RMS into 4 Ohm at 14.4V supply
Sensitivity: 50mV RMS input for full output
Frequency response:
25Hz to 20kHz -3dB with the cursor of P1 in center position
Total harmonic distortion:
0.05 - 4.5W RMS: 0.15% 6W RMS: 10%
Tone Control Frequency Response:
Tone Control Frequency
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Guitar Amplifier Circuit Diagram

10W Old-Style ultra-compact Combo, Two inputs - Overdrive - Treble-enhancement
The aim of this design was to reproduce a Combo amplifier of the type very common in the 'sixties and the 'seventies of the past century. It is well suited as a guitar amplifier but it will do a good job with any kind of electronic musical instrument or microphone. 5W power output was a common feature of these widespread devices due to the general adoption of a class A single-tube output stage (see the Vox AC-4 model). Furthermore, nowadays we can do without the old-fashioned Vib-Trem feature frequently included in those designs. The present circuit can deliver 10W of output power when driving an 8 Ohm load, or about 18W @ 4 Ohm. It also features a two-FET preamplifier, two inputs with different sensitivity, a treble-cut control and an optional switch allowing overdrive or powerful treble-enhancement.
Circuit diagram :
Guitar Amplifier Circuit Diagram
P1______________4K7 Linear Potentiometer
P2_____________10K Log. Potentiometer
R1,R2__________68K 1/4W Resistors
R3____________220K 1/4W Resistor
R4,R6,R11_______4K7 1/4W Resistors
R5_____________27K 1/4W Resistor
R7______________1K 1/4W Resistor
R8______________3K3 1/2W Resistor
R9______________2K 1/2W Trimmer Cermet
R10___________470R 1/4W Resistor
R12_____________1K5 1/4W Resistor
R13___________470K 1/4W Resistor
R14____________33K 1/4W Resistor
C1____________100pF 63V Ceramic Capacitor
C2____________100nF 63V Polyester Capacitor
C3____________470µF 35V Electrolytic Capacitor
C4____________220nF 63V Polyester Capacitor (Optional, see Notes)
C5_____________47µF 25V Electrolytic Capacitor (Optional, see Notes)
C6______________1µF 63V Polyester Capacitor
C7,C8,C9,C10___47µF 25V Electrolytic Capacitors
C11____________47pF 63V Ceramic Capacitor
C12__________1000µF 35V Electrolytic Capacitor
C13__________2200µF 35V Electrolytic Capacitor
D1_____________5mm. Red LED
D2,D3________1N4004 400V 1A Diodes
Q1,Q2________2N3819 General-purpose N-Channel FETs
Q3____________BC182 50V 200mA NPN Transistor
Q4____________BD135 45V 1.5A NPN Transistor (See Notes)
Q5____________BDX53A 60V 8A NPN Darlington Transistor
Q6____________BDX54A 60V 8A PNP Darlington Transistor
J1,J2________6.3mm. Mono Jack sockets
SW1____________1 pole 3 ways rotary switch (Optional, see Notes)
SW2____________SPST Mains switch
F1_____________1.6A Fuse with socket
T1_____________220V Primary, 48V Center-tapped Secondary 20 to 30VA Mains transformer
PL1____________Male Mains plug
SPKR___________One or more speakers wired in series or in parallel, Total resulting impedance: 8 or 4 Ohm, Minimum power handling: 20W
  • SW1 and related capacitors C4 & C5 are optional.
  • When SW1 slider is connected to C5 the overdrive feature is enabled.
  • When SW1 slider is connected to C4 the treble-enhancer is enabled.
  • C4 value can be varied from 100nF to 470nF to suit your treble-enhancement preferences.
  • In all cases where Darlington transistors are used as the output devices it is essential that the sensing transistor (Q4) should be in as close thermal contact with the output transistors as possible. Therefore a TO126-case transistor type was chosen for easy bolting on the heatsink, very close to the output pair.
  • To set quiescent current, remove temporarily the Fuse F1 and insert the probes of an Avo-meter in the two leads of the fuse holder.
  • Set the volume control to the minimum and Trimmer R9 to its minimum resistance.
  • Power-on the circuit and adjust R9 to read a current drawing of about 25 to 30mA.
  • Wait about 15 minutes, watch if the current is varying and readjust if necessary.
Technical data are quite impressive for so simple a design:
30mV input for 10W output
Frequency response:
40 to 20KHz -1dB
Total harmonic distortion @ 1KHz and 10KHz, 8 Ohm load:
below 0.05% @ 1W, 0.08% @ 3.5W, 0.15% at the onset of clipping (about 10W).
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Temperature-Controlled Switch

It sounds rather mysterious: a switch that is controlled by its ambient temperature. All without the touch of a human hand, except for when you’re building this sort of electronic thermostat. There are a lot of handy uses for a thermally controlled switch. If the temperature inside your PC gets too high sometimes, the circuit can switch on an extra fan. You can also use to switch on an electric heater automatically if the room temperature is too low. There are innumerable potential applications for the thermostat described here.

Circuit diagram:

temperature-controlled switch circuit diagram

There are lots of ways to measure the temperature of an object. One very simple way is to use a semiconductor sensor, such as the National Semiconductor LM35 IC. This sensor is accurate to within 0.5 °C at 25 ºC, and few other sensors can do better or even come close to this level of accuracy. In the circuit described here, the sensor (IC2) generates an output voltage of 10 mV/°C, so the minimum temperature that can be measured is 0 °C. At 25 °C, the output voltage of the sensor is (25 °C × 10 mV/°C) = 0.25 V.

The circuit uses a TLC271 opamp as a comparator. It compares the voltage from the temperature sensor, which is connected to its non-inverting input (pin 3), with the voltage on its inverting input (pin 2). The latter voltage can be set with potentiometer P1. If the voltage from the sensor rises above the reference value set by P1 (which represents the desired temperature), the output of the comparator toggles to the full supply voltage level. The output is fed to transistor T1, which acts as a switch so the output can handle more current.

This makes it possible to energize a relay in order to switch a heavy load or a higher voltage. The transistor also supplies current to LED D1, which indicates whether the temperature is above the reference value. The reference value can be adjusted by P1 over the range of 18–30 °C with the indicated component values. Of course, you can adjust the range to suit your needs by modifying the value of R1 and/or R2. To prevent instability in the vicinity of the reference value, a small amount of hysteresis is provided by resistor R4 so the temperature will have to continue rising or falling by a small amount (approximately 0.5 °C) before the output state changes.

The LM35 is available in several different versions. All versions have a rated temperature range of at least 0–100 °C. One thing you may have to take into account is that the sensor has a relatively long response time. According to the datasheet, the sensor takes 3 minutes to reach nearly 100% of its final value in still air. The opamp has very low drift relative to its input voltages, and in the low-power mode used here it draws very little current. The sensor also draws very little current, so the total current consumption is less than 80 µA when LED D1 is off.

The advantage of low current consumption is that the circuit can be powered by a battery if necessary (6 V, 9 V or 12 V). The sensor has a rated operating voltage range of 4–30 V, and the TLC271 is rated for a supply voltage of 3–16 V. The circuit can thus work very well with a 12-V supply voltage, which means you can also use it for car applications (at 14.4 V). In that case, you must give additional attention to filtering out interference on the supply voltage.
Source: Elektor Electronics 12-2010
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When The Siren Sounds - A Useful Circuit

In Greek mythology, a siren was a demonic being (half bird, half woman). Later on this idea was transformed in art into a mermaid: a combination of a fish and a woman. Mechanical and electromechanical versions were invented even later, and electronic models were developed in the last century. Sirens are characterized by their ability to produce sounds that attract attention. With the exception of the flesh-and-blood models, they are thus used to warn people in a particular area of impending danger. The electronic versions are the most suitable for DIY construction.

Circuit diagram:
siren circuit diagram

There are lots of different ways to make an electronic siren. Here we use a binary counter (IC1) and an analogue multiplexer (IC2, which is a digitally configurable switch). The counter is a type 4060 IC, which has an integrated oscillator. The oscillator generates the tone of the siren. The frequency of this tone depends on the resistance between pin 10 of IC1 and the junction of C1 and R9. The trick here is that the analogue multiplexer adjusts the clock rate of the counter depending on the state of the counter.

The frequency of the oscillator decreases as the resistance between pin 10 of IC1 and the junction of C1 and R9 increases, and the lower the frequency of the oscillator, the longer the counter remains in its current state. This means that high frequencies present on pin 9 are generated for shorter times than low frequencies. The values of resistors R1–R8 increase in uniform steps of approximately 10kO, with the result that the output on pin 9 is a series of eight decreasing frequencies, and this series is constantly repeated in cyclical fashion. Transistor T1 (BD139) and resistor R10 are included to boost the signal from pin 9 to a level suitable for driving a loudspeaker.

The sound produced by this circuit may be familiar to some of our readers (especially if their memories extend back to older types of pinball and arcade game machines). You can also adjust the characteristics of the sound, since this circuit is primarily an invitation to experiment with the component values – in particular R1–R8 (10 k? minimum), but also C1. The values of R1–R8 do not have to follow a strictly increasing series; they can also be selected randomly. The current consumption is primarily determined by resistor R10 and the loudspeaker (in our case an 8-O type). The siren circuit draws approximately 33 mA at a supply voltage of 9 V. The supply current is 11 mA at the minimum supply voltage of 4 V, and it increases to 60 mA at the maximum supply voltage of 15 V.
Source: Elektor Electronics 12-2006
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Surf Simulator Circuit Diagram

Do you long for a beach holiday on a tropical island, but you don’t have the necessary wherewithal? We’ve got just the answer: build the i-TRIXX surf simulator, put on your headphones, and dream yourself away from this dreary realm. Let the rhythmic rush of the waves transport you to a sun-drenched beach with gently swaying palm trees, and relax for a while before returning to a chilly confrontation with reality. That’s the ultimate in low-budget travel.

Book now! Isn’t it great to relax on the snow-white sand of a tropical beach with a cool drink in your hand? To enjoy the magnifi cent of earthly creation while letting your thoughts drift on the hypnotic mantra of the breaking surf? No relaxant brewed by human hands can possibly compete with it! But when you start thinking about how much it all costs, you’ll reach for the headache pills instead. Fortunately, there’s a less expensive way to relax — with a bit of electronics that imitates the soothing sound of the sea.

You’ll have to imagine the corresponding surroundings on your own. A sunlamp and a few scoops of sand may help…This circuit uses more components that most of the i-TRIXX do it yourself projects, but this doesn’t make it harder to understand how it works. We have also designed a PCB layout for the circuit, which makes DIY construction that much easier. Noise is usually the last thing you want in any sort of audio circuitry. Noise is generated in semiconductor devices (transistors and diodes) as an undesirable by-product.

Circuit diagram:
surf simulator circuit schematic

However, in our surf simulator we just can’t get enough of it! Noise forms the basis for imitating the sound of breaking surf. We take advantage of the fact that a reverse-biased base–emitter junction of a transistor generates noise like the devil if the voltage is high enough. The noise source in the schematic diagram is transistor T1. The base–emitter junction of this transistor breaks down at approximately 7 V (depending on the specific transistor). R1 limits the current to a level that avoids destroying the transistor.

T1 generates a constant noise signal, which doesn’t resemble the sound of breaking surf. If you listen carefully to the sound of real surf, you’ll notice that it resembles a noise signal that increases rapidly in volume (as the wave rolls up the beach) and then slowly dies down. This means the noise must rise and decay in a sawtooth waveform. To achieve this effect, we make use of the AC impedance of a normal diode (D1 in the schematic diagram), which depends on the amount of DC current fl owing through the diode. The higher the current through the diode, the lower its AC impedance (and thus its impedance to the noise signal).

The voltage across R10 determines how much current flows through diode D1. The noise signal is amplified by IC1d and applied to the diode, and the voltage across the diode is further amplified by IC1c to the output level. As already mentioned, the amplitude of the noise signal depends on the DC current through diode D1. What we have to do now is make the current through D1 (or in other words, the voltage across R10) vary in a sawtooth pattern. This job is handled by amplifiers IC1a and IC1b.

You can use P1 to adjust the form of the sawtooth (and thus how the noise grows and decays) according to your taste. The circuit works best with a clean 9-V supply voltage, so an AC mains adapter with a stabilized 9-V output is the preferred choice as a power source. A balanced supply voltage is required for proper operation of the circuit, so a virtual ground is necessary.

PCB layout:
pcb layout of surf simulator circuit schematic
R1,R2,R6 = 1 MΩ
R3 = 4kΩ7
R4,R8,R10,R14,R16 = 100 kΩ
R5 = 22 kΩ
R7,R12 = 10 kΩ
R9 = 1 kΩ
R11 = 120 kΩ
R13 = 2MΩ2
R15 = 33 kΩ
R17 = 220 kΩ
R18 = 3kΩ9
R19 = 2kΩ2
P1 = 2MΩ5 preset
C1,C10,C11 = 100 nF
C2,C5 = 47 pF
C3,C6 = 220 nF
C4 = 3nF3
C7 = 47 µF/25V radial
C8 = 2µ2 MKT lead pitch 5 or 7.5mm
C9 = 220 µF/25V radial
D1,D2 = 1N4148
D3 = LED, 3mm, green, low current
T1 = BC547B
IC1 = TL084

6 PCB solder pins
BT1 = 9V battery with clip-on leads
(however 9 V battery eliminator

This is created in a simple manner by a voltage divider (R18 and R19). To reduce the current consumption (in case you want to power the circuit from a battery), it also provides a ‘power on’ indication. The current consumption of the circuit is approximately 9 mA, which means the battery would have to be replaced already after two days of continuous use if it is powered by a battery, so using an AC mains adapter is certainly advisable. We designed a PCB layout for this project to make it easier to assemble, since it is a bit more complex than most of the i-TRIXX circuits.

If you follow the illustrated component layout, you shouldn’t have any trouble at all. The idea here is that you print the copper layout at actual size (52 × 52 mm) on transparent film. The easiest way to do this is to use the supplied pdf fi le which you can open with Adobe Reader. You can then use the fi lm to expose a circuit board, develop it, and then etch it. Alternatively, you can take the fi lm to your local electronics shop and have them make a board for you.
Source: Elektor Electronics 12-2006
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