Schematic Reference

The circuit is intended for carrying out harmless experiments with high-voltage pulses and functions in a similar way as an electrified fence generator. The p.r.f. (pulse repetition frequency) is determined by the time constant of network R1-C3 in the feedback loop of op amp IC1a: with values as specified, it is about 0.5 Hz. The stage following the op amp, IC1b, converts the rectangular signal into narrow pulses. Differentiating network R2-C4, in conjunction with the switching threshold of the Schmitt trigger inputs of IC1b, determines the pulse period, which here is about 1.5 ms. The output of IC1b is linked directly to the gate of thyristor THR1, so that this device is triggered by the pulses.

The requisite high voltage is generated with the aid of a small mains transformer, whose secondary winding is here used as the primary. This winding, in conjunction with C2, forms a resonant circuit. Capacitor C3 is charged to the supply voltage (12 V) via R3.When a pulse output by IC1b triggers the thyristor, the capacitor is discharged via the secondary winding. The energy stored in the capacitor is, however, not lost, but is stored in the magnetic field produced by the transformer when current flows through it. When the capacitor is discharged, the current ceases, whereupon the magnetic field collapses. This induces a counter e.m.f. in the transformer winding which opposes the voltage earlier applied to the transformer.

This means that the direction of the current remains the same. However, capacitor C2 is now charged in the opposite sense, so that the potential across it is negative. When the magnetic field of the transformer has returned the stored energy to the capacitor, the direction of the current reverses, and the negatively charged capacitor is discharged via D1 and the secondary winding of the transformer. As soon as the capacitor begins to be discharged, there is no current through the thyristor, which therefore switches off. When C2 is discharged further, diode D1 is reverse-biased, so that the current loop to the transformer is broken, whereupon the capacitor is charged to 12 V again via R3. At the next pulse from IC1b, this process repeats itself.

Since the transformer after each discharge of the capacitor at its primary induces not only a primary, but also a secondary voltage, each triggering of the thyristor causes two closely spaced voltage pulses of opposite polarity. These induced voltages at the secondary, that is, the 230 V, winding, of the transformer are, owing to the higher turns ratio, much higher than those at the primary side and may reach several hundred volts. However, since the energy stored in capacitor C2 is relatively small (the current drain is only about 2mA), the output voltage cannot harm man or animal. It is sufficient, however, to cause a clearly discernible muscle convulsion.

This circuit can be used for inductive pick-up elements and dynamic microphones Most soundcards have a ‘line’ input and one for an electret (condenser) microphone. To be able to connect an inductive tape-recorder head or a dynamic microphone, an add-on preamplifier is needed. Even in this day and age of integrated microelectronics, a transistorised circuit built from discrete part has a right of existence. The preamplifier described in this short article goes to show that it will be some time before discrete transistors are part of the silicon heritage. The preamplifier is suitable for use with a soundcard or the microphone input of a modem. As you will probably know, most sound-cards have input sockets for signals at line level (stereo), as well as one for a (mono) electret microphone.

For the applications we have in mind, connecting-up an inductive pick-up element or a dynamic microphone, both inputs are in principle suitable, provided the source signal is amplified as required. The author eventually chose the microphone input on the soundcard. Firstly, because the line inputs are usually occupied, and secondly, because the bias voltage supplied by the micro-phone input eliminates a separate power supply for the preamplifier. The microphone input of a soundcard will typically consist of a 3.5-mm jack socket in stereo version, although only one channel is available. The free contact is used by the soundcard to supply a bias voltage to the mono electret microphone. This voltage is accepted with thanks by the present preamplifier, and conveniently obviates an external (mains adaptor) power supply.

A classic design:

In true transistor-design fashion, the preamplifier consists of three stages. Capacitor C1 decouples the signal received from the microphone or pick-up element, and feeds it to the input of the first stage, a transistor in emitter configuration, biased to provide a current amplification of about 300 times. Together with the source impedance of the microphone or pick-up element, capacitors C2 and C3 form a low-pass filter which lightly reduces the bandwidth. In addition, the output low-pass, R2-C3, reduces the dynamic collector resistance at higher frequencies. In this way, the filter reduces the gain in the higher part of the frequency spectrum and so helps to eliminate any oscillation tendencies.

The first, high-gain, stage is terminated by T2. Unlike T1, this transistor does not add to the overall gain, because the output signal is taken from the emitter (common-collector circuit). T2 thus acts as an impedance converter, with C4 reducing any tendency to oscillation. The output stage around T3 is a common-emitter circuit again. In it, preset P1 determines the voltage amplification. T3 is biased by means of a direct-current feedback circuit based on components R7 and C5. To this is added an ‘overruling’ dc feedback path back to the input transistor, via R6. This measure guarantees good dc stability in the preamplifier. The circuit is small enough to be built on a piece of veroboard or stripboard, and yet remain reasonably compact.

To prevent interference from external sources, the completed board should be mounted in a properly screened (metal) enclosure, with the connections to the input source and the sound card made in screened cable. The preamplifier provides a frequency-linear response. In case the source signal is marked by frequency correction (e.g., RIAA), then a matching linearization circuit should be used if the relevant signals are used by the computer.

This project consists of a small, portable DJ mixer powered by a 9V dc external supply adaptor or from a 9V PP3 battery. The mixer features two stereo phono inputs and two stereo line-level inputs and has one stereo mixing channel. A microphone input and a stereo main output with adjustable gain are also provided. Headphone monitoring includes a cue switch for selecting Channel 1, Channel 2 or Master Channel. For easy understanding, the circuit is divided into five blocks, as follows:

General Circuit diagram:all passive circuitry (controls, faders, switches, input and output connectors) is shown in full, whereas active amplification modules are represented by suitably labeled triangle symbols.
Phono Amplifier Module: a high gain stereo amplifier suitable for moving magnet pick-up cartridges, having a frequency response according to RIAA equalization curve and based on the low noise, low distortion LS4558 dual IC. Two identical stereo modules of this type are required.
Microphone Amplifier Module: a single transistor, low noise, high gain microphone amplifier, suitable for low impedance microphones.
Mixer Module: a stereo circuit incorporating two virtual-earth mixers based on the dual BIFET TL062 Op-Amp.
Headphone Amplifier Module: this circuit was already present on this website under Portable 9V Headphone Amplifier. It features a low current drain stereo amplifier based on the low distortion, low noise 5532 dual IC, capable of delivering 3.6V peak-to-peak into 32 Ohm load at 9V supply (corresponding to 50mW RMS) with less than 0.025% total harmonic distortion (1kHz & 10kHz).

General Circuit Diagram:

P1,P2,P4,P5____22K Dual gang Log Potentiometers
P3_____________22K Dual gang Linear Potentiometer
P6_____________22K Log Potentiometer
R1 to R10______30K 1/4W 1% or 2% tolerance Resistors
R11_____________1K 1/4W Resistor
C1___________2200µF 25V Electrolytic Capacitor
D1_____________3mm. or 6mm. red LED
J1 to J10______RCA audio input sockets
J11____________6mm. or 3.5mm. Stereo Jack socket
J12____________6mm. or 3.5mm. Mono Jack socket
J13____________Mini DC Power Socket
SW1,SW2________DPDT toggle or slide Switches
SW3____________2 poles 3 ways Rotary Switch
SW4____________SPST toggle or slide Switch

Circuit description:

The input source can be selected by means of SW1 for Channel 1 and SW2 for Channel 2. Moving magnet pick-ups must be connected to Phono 1 and 2 inputs, whereas CD players, iPods, Tape recorders, PC Audio outputs and the like can be connected to Line 1 and 2 inputs. After a separate Level control for each channel (P1 and P2), the two incoming audio signals are mixed and cross-faded by means of P3 and associated resistors network. The Crossfader control mixes both Channels at the same intensity when set in the middle position. When the cursor of P3 is fully rotated towards R3-R4, only Channel 1 signal is present at the Main output, whereas Channel 2 is muted.

Conversely, Channel 2 signal is present at the Main output and Channel 1 is muted when the cursor of P3 is fully rotated towards R1-R2. This network is followed by the Mixer Amplifier, the Master Level P4 and the Main output sockets. A low impedance microphone can be connected to the Mic input. P6 controls the signal level after amplification by the Microphone Amplifier module and feeds the Left and Right Mixer Amplifiers through R9-R10. In this way, the speaker's voice will be reproduced at the center of the soundstage.

A stereo Headphone Amplifier with cue gain control is provided for monitoring purposes. The Cue Select switch SW3 will allow Headphone reproduction of Channel 1, Channel 2 or Master Channel, independently of the signal present at the Main Output. J13 is a Mini DC Power Socket into which the suitable plug of a 9V dc external supply adaptor should be inserted. In any case, due to the low total current drain (about 13mA average), a 9V battery can be used satisfactorily to power the entire Station.

Magnetic Pick-up Amplifier Module

R1,R10__________2K2 1/4W Resistors
R2,R3,R11,R12_100K 1/4W Resistors
R4,R13__________1K 1/4W Resistors
R5,R6,R14,R15__18K 1/4W Resistors
R7,R16________390K 1/4W Resistors
R8____________220R 1/4W Resistor
R9,R17_________10K 1/4W Resistors
C1,C5,C6,C10___22µF 25V Electrolytic Capacitors
C2,C7__________47µF 25V Electrolytic Capacitors
C3,C8___________2n2 63V Polyester or Polystyrene low tolerance Capacitors
C4,C9__________10nF 63V Polyester or Polystyrene low tolerance Capacitors
C11___________100µF 25V Electrolytic Capacitor
IC1__________LS4558 Dual High Performance Op-Amp

Circuit description:

A straightforward series-feedback amplifier circuit with RIAA frequency compensation, based on the High Performance LS4558 Op-Amp was used for this stage.
Despite the low supply voltage operation, the performance of this Circuit Module is quite good.

Note:

• Two identical stereo modules of this type are required.
• A more strict RIAA equalization curve will be obtained if low tolerance components are used for R5, R6, R7, R14, R15, R16 (1% - 2%) and C3, C4, C8, C9 (2% - 5%).

Microphone Amplifier Module

R1______________1M2 1/4W Resistor
R2______________5K6 1/4W Resistor
R3______________1K 1/4W Resistor
C1,C3___________4µ7 63V Electrolytic Capacitors
C2____________100µF 25V Electrolytic Capacitor
Q1____________BC550C 45V 100mA Low noise High gain NPN

Circuit description:

This circuit module, based on a very simple, single transistor amplifier, features a low noise, 45dB stage gain. Input impedance: 2700 Ohm.

Mixer Module

R1,R2,_________68K 1/4W Resistors
R3,R4_________120K 1/4W Resistors
C1,C2,C4,C6,C8__4µ7 63V Electrolytic Capacitors
C3,C7__________10pF 63V Ceramic Capacitors
C5____________100µF 25V Electrolytic Capacitor
IC1___________TL062 Low current BIFET Dual Op-Amp

Circuit description:

Straightforward virtual-earth mixer-amplifier stage based on the very low current drawing BIFET TL062 Op-Amp.

Headphone Amplifier Module:

R1,R5___________18K 1/4W Resistors
R2,R3,R4,R6_____68K 1/4W Resistors
C1,C2,C6_________4µ7 25V Electrolytic Capacitors
C3,C7___________22pF 50V Ceramic Capacitors
C4,C5,C8_______220µF 25V Electrolytic Capacitors
IC1___________NE5532 Low noise Dual Op-amp

Circuit description:

For a complete description of this stage see: Portable 9V Headphone Amplifier.

Technical data:

Sensitivity:
Microphone Input: 3.5mV RMS
Phono Input: 8mV RMS
Line Input: 500mV RMS

Maximum undistorted output:
Main output: 2.5V RMS
Headphones: 1.27V RMS into 32 Ohm load

Frequency response:
Microphone and Line: flat from 20Hz to 20KHz
Phono: according to RIAA curve ±1dB
Headphones: flat from 40Hz to 20KHz; -2.3dB @ 20Hz

Total harmonic distortion @ 1KHz and 1V RMS output:
Line: 0.013%
Phono: 0.016%
Headphones: 0.025%

Total current drawing @ 9V supply:
Standing current: 10mA
Mean current drawing: 13mA

Wireless portable unit, Adaptable with most internal combustion engine vehicles
This circuit has been designed to alert the vehicle driver that he/she 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 diagram: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

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 allowing 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 savings.
• 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 vehicle'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.
• Current drawing is about 10mA. If you intend to use the car 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 pin 6. Connect the generator output across C2 and Ground. Set the generator frequency to e.g. 100Hz and trim R11 until you will hear the beeps and LED D5 will start flashing. Reducing the frequency to 99 or 98 Hz, beeping and flashing must stop.
• Please note that this circuit is not suited to Diesel engines.

This design was primarily intended to allow automatic switch-on of push-bike lights when it gets dark. Obviously, it can be used for any other purpose involving one or more lamps to be switched on and off depending of light intensity. Power can be supplied by any type of battery suitable to be fitted in your bike and having a voltage in the 3 to 6 Volts range. The Photo resistor R1 should be fitted into the box containing the complete circuit, but a hole should be made in a convenient side of the box to allow the light hitting the sensor. Trim R2 until the desired switching threshold is reached. The setup will require some experimenting, but it should not be difficult.

Parts:

R1_____________Photo resistor (any type)
R2______________22K 1/2W Trimmer Cermet or Carbon type
R3_______________1K 1/4W Resistor
R4_______________2K7 1/4W Resistor
R5_____________330R 1/4W Resistor (See Notes)
R6_______________1R5 1W Resistor (See Notes)
D1____________1N4148 75V 150mA Diode
Q1_____________BC547 45V 200mA NPN Transistor
Q2_____________BD438 45V 4A PNP Transistor
LP1____________Filament Lamp(s) (See Notes)
SW1_____________SPST Toggle or Slider Switch
B1______________6V or 3V Battery (See Notes)

Notes:

• In this circuit, the maximum current and voltage delivered to the lamp(s) are limited mainly by R6 (that can't be omitted if a clean and reliable switching is expected). Therefore, the Ohm's Law must be used to calculate the best voltage and current values of the bulbs.
• For example: at 6V supply, one or more 6V bulbs having a total current drawing of 500mA can be used, but for a total current drawing of 1A, 4.5V bulbs must be chosen, as the voltage drop across R6 will become 1.5V. In this case, R6 should be a 2W type.
• At 3V supply, R6 value can be lowered to 1 or 0.5 Ohm and the operating voltage of the bulbs should be chosen accordingly, by applying the Ohm's Law.
• Example: Supply voltage = 3V, R6 = 1R, total current drawing 600mA. Choose 2.2V bulbs as the voltage drop caused by R6 will be 0.6V.
• At 3V supply, R5 value must be changed to 100R.
• Stand-by current is less than 500µA, provided R2 value after trimming is set at about 5K or higher: therefore, the power switch SW1 can be omitted. If R2 value is set below 5K the stand-by current will increase substantially.

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.

Parts:

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

Notes:

• 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:
Sensitivity:
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).

4 - 6 - 8 - 12 - 24 - 48 hours setting, LED or Beep Alert - 9V Battery Supply
A Pills Reminder is a device that operates a flashing LED (and/or a beeper) at a fixed hour interval. A choice of time-intervals as wide as possible is available with this circuit, namely 4, 6, 8, 12, 24 and 48 hours. At first you must choose the hour interval by switching SW1 to the desired value, then apply power by means of SW2. After the hour delay chosen has elapsed the LED will start flashing at 2Hz, i.e. two times per second. This status will last until pushbutton P1 is pressed: then the LED will turn off, but the circuit will continue its counting and the LED will flash again when the same hour interval as before is reached. A noteworthy feature of this circuit, usually not found in similar devices, is that the internal counter is not reset when P1 is pressed: this allows a better time-interval precision.

Let us explain this feature with an example: suppose you have set the time interval to 24 hours and started the Pills Reminder at 8 o'clock. Next day, at 8 o'clock the LED will start flashing, but you, for some reason, notice the flashes at 8:10 and press P1 to stop the LED. With most devices of this kind, the counter will be reset, causing the LED to start flashing next day at 8:10 o'clock. This will not happen with this circuit and the LED will start flashing next day always precisely at 8 o'clock even if you pressed P1 at 9 or 10 o'clock.

Parts:

R1______________10M 1/4W Resistor
R2,R3,R4_______100K 1/4W Resistors
R5,R7___________10K 1/4W Resistors
R6_______________1K 1/4W Resistor
C1,C2___________22pF 63V Ceramic Capacitors (See Notes)
C3______________22µF 25V Electrolytic Capacitor
C4,C5__________100nF 63V Polyester Capacitors
C6_______________1µF 63V Polyester, Multilayer Ceramic or Electrolytic Capacitor
IC1____________4060 14 stage ripple counter and oscillator CMos IC
IC2____________4040 12 stage ripple counter CMos IC
IC3____________4082 Dual 4 input AND gate CMos IC
IC4____________4075 Triple 3 input OR gate CMos IC
IC5____________4520 Dual binary up-counter CMos IC
IC6____________4001 Quad 2 input NOR Gate CMos IC
D1_____________5 or 10mm red LED
XTAL_________32.768 kHz Sub-miniature Watch crystal
P1_____________SPST Pushbutton
SW1____________2 poles 6 ways Rotary Switch
SW2____________SPST Toggle or Slide Switch
B1_______________9V PP3 Battery Clip for PP3 Battery

Alternative Clock Parts:

R8_______________1K 1/4W Resistor
R9_____________330K 1/4W Resistor
R10_____________20K 1/2W Cermet or Carbon Trimmer
R11______________1K 1/2W Cermet or Carbon Trimmer
C7_______________1µF 63V Polyester Capacitor
IC7____________7555 or TS555CN CMos Timer IC

Circuit Operation:

The clock of the circuit is made of a stable oscillator built around two inverters embedded into IC1 and a Watch crystal oscillating at 32.768kHz. This frequency is divided by 16384 by the internal flip-flop chain of IC1 and a 2Hz very stable clock frequency is available at pin #3 of this IC. IC2 counter and IC3A 4 input AND gate are wired in order to divide by 3600 the 2Hz clock, therefore, a pulse every 30 minutes is available at the clock input of IC5. The division factor of this IC is controlled by IC3B and the position of SW1A and B, selecting from six time-intervals fixed to 4, 6, 8, 12, 24 and 48 hours.

The set-reset flip-flop formed by IC6B and IC6C is set through IC4C each time a low to high transition is present at the pin of IC5 selected by SW1B cursor. IC6A and C4 provide to set the flip-flop also when a high to low transition is present at SW1B cursor. When the flip-flop is set, IC6D is enabled and the 2Hz frequency available at pin #3 of IC1 is applied to pin #13 of IC6D causing the flashing LED operation. The flip-flop can then be reset by means of P1. A master reset is automatically done at switch on by means of C6 and R7.

Alternative Clock:

Sometimes, the Watch crystal can be difficult to locate, or could be considered too expensive. For those willing to avoid the use of a Watch crystal and to accept less time accuracy, an alternative clock generator circuit is provided, directly oscillating at 2Hz, thus avoiding the use of divider ICs. A CMos 7555 Timer IC generates a stable 2Hz square wave, whose frequency must be accurately set by means of two trimmers. R10 must be adjusted first for coarse tuning, then R11 for fine tuning. Setting precisely the 2Hz frequency of this oscillator is a rather difficult task, and can be done with great patience and the aid of a clock, a chronometer or, best, a digital frequency meter capable of measuring very low frequencies. In any case, after an accurate setup, this oscillator showed a very stable performance, not affected by battery voltage variations and an accuracy of about ±30 seconds per 24 hours interval.

Notes:

• Wanting the utmost time precision and if a digital frequency meter is available, a 5-50pF 50V Ceramic Trimmer Capacitor can be used in place of C2. It must be adjusted in order to read exactly 32.768kHz on the meter display with the input probe connected to pin #9 of IC1.
• A Piezo sounder (incorporating a 3KHz oscillator) can be added to provide a visual plus audible alert. It must be wired across pin #11 of IC6D and negative ground, respecting polarities. Remove D1 and R6 if the visual alert is not needed.

Three LEDs signal bumper-barrier distance, Infra-red operation, indoor use
This circuit was designed as an aid in parking the car near the garage wall when backing up. LED D7 illuminates when bumper-wall distance is about 20 cm., D7+D6 illuminate at about 10 cm. and D7+D6+D5 at about 6 cm. In this manner you are alerted when approaching too close to the wall. All distances mentioned before can vary, depending on infra-red transmitting and receiving LEDs used and are mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device sensitivity. Obviously, you can use this circuit in other applications like liquids level detection, proximity devices etc.

Parts:

R1_____________10K 1/4W Resistor
R2,R5,R6,R9_____1K 1/4W Resistors
R3_____________33R 1/4W Resistor
R4,R11__________1M 1/4W Resistors
R7______________4K7 1/4W Resistor
R8______________1K5 1/4W Resistor
R10,R12-R14_____1K 1/4W Resistors
C1,C4___________1µF 63V Electrolytic or Polyester Capacitors
C2_____________47pF 63V Ceramic Capacitor
C3,C5_________100µF 25V Electrolytic Capacitors
D1_____________Infra-red LED
D2_____________Infra-red Photo Diode (see Notes)
D3,D4________1N4148 75V 150mA Diodes
D5-7___________LEDs (Any color and size)
IC1_____________555 Timer IC
IC2___________LM324 Low Power Quad Op-amp
IC3____________7812 12V 1A Positive voltage regulator IC

Circuit operation:

IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the car on the same line, a couple of centimeters apart, on a short breadboard strip fastened to the wall. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting inputs of three voltage comparators. These comparators switch on and off the LEDs, referring to voltages at their non-inverting inputs set by the voltage divider resistor chain R7-R10.

Circuit modification:

A circuit modification featuring an audible alert instead of the visual one is available here: Park-Aid Modification

Notes:

• Power supply must be regulated (hence the use of IC3) for precise reference voltages. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.
• Current drawing: LEDs off 40mA; all LEDs on 60mA @ 12V DC supply.
• The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.
• Avoid sun or artificial light hitting directly D1 & D2.
• If your car has black bumpers, you can line-up the infra-red diodes with the (mostly white) license or number plate.
• It is wiser to place all the circuitry near the infra-red LEDs in a small box. The 3 signaling LEDs can be placed far from the main box at an height making them well visible by the car driver.
• The best setup is obtained bringing D2 nearer to D1 (without a reflecting object) until D5 illuminates; then moving it a bit until D5 is clearly off. Usually D1-D2 optimum distance lies in the range 1.5-3 cm.
• If you are needing a simpler circuit of this kind driving a LED or a relay, click Infra-red Level Detector

Processor based systems usually require a voltage supervisor chip to produce a clean reset pulse to the processor whenever a ‘brown-out’ condition of the power supply is detected. More complex designs employing multiple power supplies can be unreliable if some of the supplies are not supervised. The circuit described here monitors all the supply rails in the system (here +12 V, –12 V and +5 V) and provides a reset pulse to the processor whenever it detects any are not within tolerance. IC1 (TL7705A) generates a processor reset if the 5 V rail falls below 4.55 V. The value of the capacitor fitted to pin 3 defines the reset pulse width td according to the formula: td = 12 . CT 3 103 With CT in µF the value for td is given in µs.

A capacitor of 100 nF for example, will produce a reset pulse of around 1.2 ms. Pin 6 (RESET) outputs an active-high pulse and Pin 5 (RESET) an active-low pulse. The outputs are open collector types so an external pull-down and pull-up resistor (respectively) is required. The RESIN input (Pin 2) of IC1 is driven from two TL7712A supervisors monitoring +12 V (IC2) and –12 V (IC3). The TL7712A generates a reset when the supply voltage falls below a threshold level of 10.8 V. The open collector output RES (Pin 5) of IC2 is connected to the RESIN pin of IC1 and pulled up to 5 V via a 100 k? resistor. The open collector output of IC2 can be directly connected to the reset input of IC1 but the output of IC3 must be connected via a level shifting device before it can be connected to the reset input of IC1 because the voltage level at the output of IC3 goes negative.

JFET transistor T1 is used to perform the necessary level shifting. The JFET turns off when the voltage at its gate-source junction is between –2.5 V and –6 V. When IC3 is issuing a reset signal the RES output (pin 6) will go up to ground potential and cause T1 to conduct and trigger a reset of IC1. At all other times the RES output of IC3 will be pulled to a minus voltage via the 100 k? resistor which then causes T1 to stop conducting and release the reset. A manual reset push button can also be connected to RESIN of IC1 if required. The SENSE input (Pin 7) of the TL77xx chips is connected to the positive supply rail. The reference input (pin 1) is fitted with a 100 nF capacitor to reduce the effects of fast transients.

Crystals usually operate at fundamental frequencies up to about 15 MHz. Whenever higher frequencies are required a frequency multiplier is placed after the crystal oscillator. The resulting output signal is then a whole multiple of the crystal frequency. Other frequency multipliers often use transistors, which produce harmonics due to their non-linearity. These are subsequently filtered from the signal. One way of doing this is to put a parallel L-C filter in the collector arm. This filter could then be tuned to three times the input frequency. A disadvantage is that such a circuit would quickly become quite substantial.

This circuit contains only a single IC and a handful of passive components, and has a complete oscillator and two frequency triplers. The output is therefore a signal with a frequency that is 9 times as much as that of the crystal. Two gates from IC1, which contains six high-speed CMOS inverters, are used as an oscillator in combination with X1. This works at the fundamental frequency of the crystal and has a square wave at its output. A square wave can be considered as the sum of a fundamental sine wave plus an infinite number of odd multiples of that wave. The second stage has been tuned to the first odd multiple (3 x).

We know that some of our readers will have noticed that the filter used here is a band-rejection (series LC) type. Worse still, when you calculate the rejection frequency you’ll find that it is equal to the fundamental crystal frequency! The fundamental frequency is therefore attenuated, which is good. But how is the third harmonic boosted? That is done by the smaller capacitor of 33 pF in combination with the inductor. Together they form the required band-pass filter. (The same applies to the 12 pF capacitor in the next stage.) Through the careful selection of components, this filter is therefore capable of rejecting the fundamental and boosting the third harmonic! Clever, isn’t it?.

The output in this example is a signal of 30 MHz. The inverter following this stage heavily amplifies this signal and turns it into a square wave. The same trick is used again to create the final output signal of 3 times 30 MHz = 90 MHz. At 5 V this circuit delivers about 20 milliwatt into 50 R. This corresponds to +13 dBm and is in theory enough to drive a diode-ring balanced mixer directly. The circuit can be used for any output frequency up to about 100 MHz by varying the component values. When, for example, an 8 MHz crystal is used to obtain an output frequency of 72 MHz (9 x 8 = 72), the frequency determining inductors and capacitors have to be adjusted by a factor of 10/8.

You should round the values to the nearest value from the E12 series. Another application is for use in an FM transmitter; if you connect a varicap in series with the crystal, you can make an FM modulator. An added bonus here is that the relatively small modulation level is also increased by a factor of 9. Crystals with frequencies near 10 MHz are relatively easy to find and inexpensive, so you should always be able to find a suitable frequency within the FM band. A crystal of 10.245 MHz for instance would give you a frequency of 92.205 MHz and 10.700 MHz results in an output of 96.300 MHz. You may find that the circuit operates on the border of the HC specifications. If this causes any problems you should increase the supply voltage a little to 6V.

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The information in this manual supplements the owner manual. This manual describes features that may or may not be on your specific vehicle either because they are options that you did not purchase or due to changes subsequent to the printing of this owner manual. Please refer to the purchase documentation relating to your specific vehicle to confirm each of the features found on your vehicle. For vehicles first sold in Canada, substitute the name “General Motors of Canada Limited” for Chevrolet and GMC Motor Divisions wherever it appears in this manual. download here

This 2012 GMC Terrain owner Manual describes features that may or may not be on your specific vehicle either because they are options that you did not purchase or due to changes subsequent to the printing of this owner manual. Please refer to the purchase documentation relating to your specific vehicle to confirm each of the features found on your vehicle.

For vehicles first sold in Canada, substitute the name “General Motors of Canada Limited” for GMC Motor Division wherever it appears in this manual. Download 2012 GMC Terrain Owners Manual