Loublet Schematic

Friday, October 17, 2014

Test Beeper For Your Stereo

The test beeper generates a sinusoidal signal with a frequency of 1,000 Hz, a common test frequency for audio amplifiers. It consists of a classical Wien- Bridge oscillator (also known as a Wien-Robinson oscillator). The network that determines the frequency consists here of a series connection of a resistor and capacitor (R1/C1) and a parallel connection (R2/C2), where the values of the resistors and capacitors are equal to each other. This network behaves, at the oscillator frequency (1 kHz in this case), as two pure resistors. The opamp (IC1) ensures that the attenuation of the net- work (3 times) is compensated for. In principle a gain of 3 times should have been sufficient to sustain the oscillation, but that is in theory. Because of tolerances in the values, the amplification needs to be (automatically) adjusted.

Test Beeper For Your Stereo Circuit diagram:

Test Beeper For Your Stereo circuit Diagram

Instead of an intelligent amplitude controller we chose for a somewhat simpler solution. With P1, R3 and R4 you can adjust the gain to the point that oscillation takes place. The range of P1 (±10%) is large enough the cover the tolerance range. To sustain the oscillation, a gain of slightly more than 3 times is required, which would, however, cause the amplifier to clip (the ‘round-trip’ signal becomes increasingly larger, after all). To prevent this from happening, a resistor in se-ries with two anti-parallel diodes (D1 and D2) are connected in parallel with the feedback (P1 and R3). If the voltage increases to the point that the threshold voltage of the diodes is exceed-ed, then these will slowly start to conduct.

The consequence of this is that the total resistance of the feedback is reduced and with that also the amplitude of the signal. So D1 and D2 provide a stabilising function. The distortion of this simple oscillator, after adjustment of P1 and an output voltage of 100 mV (P2 to maximum) is around 0,1%. You can adjust the amplitude of the output signal with P2 as required for the application. The circuit is powered from a 9-V battery. Because of the low current consumption of only 2 mA the circuit will provide many hours of service.

Author :Ton Giesberts - Copyright : Elektor Electronics

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Monday, August 25, 2014

Simple Timed Beeper Wiring diagram Schematic

Hi Everyone Yesterday upon visiting my (somewhat) local optometrist, I was advised to look up every 5 minutes or my eyes will stay

Simple Timed Beeper Circuit Diagram

Parts:

R1______220R1/4W Resistor

R2_______10M1/4W Resistor

R3________1M1/4W Resistor

R4_______10K1/4W Resistor

R5_______47K1/4W Resistor

C1_______100nF63V Polyester Capacitor

C2________22µF25V Electrolytic Capacitor

D1______1N414875V 150mA Diode

D2________3mm.Red LED

IC1_____4081Quad 2 input AND Gate IC

IC2_____406014 stage ripple counter and oscillator IC

Q1______BC33745V 800mA NPN Transistor

P1______SPST Pushbutton (Start)

P2______SPST Pushbutton (Reset)

SW1_____4 ways Switch (See notes)

PS______Piezo sounder (incorporating 3KHz oscillator)

B1______3V Battery (2 AA 1.5V Cells in series)

Device purpose:

This schema is intended for alerting purposes after a certain time is elapsed. It is suitable for table games requiring a fixed time to answer a question, or to move a piece etc. In this view it is a modern substitute for the old sand glass. Useful also for time control when children are brushing teeth (at least two minutes!), or in the kitchen, and so on.

Circuit operation:

Pushing on P1 resets IC2 that start oscillating at a frequency fixed by R3 & C1. With values shown, this frequency is around 4Hz. LED D2, driven by IC1A & B, flashing at the same oscillator frequency, will signal proper schema operation. SW1 selects the appropriate pin of IC2 to adjust timing duration:

Position 1 = 15 seconds
Position 2 = 30 seconds
Position 3 = 1 minute
Position 4 = 2 minutes

When the selected pin of IC2 goes high, IC1C drives Q1 and the piezo sounder beeps intermittently at the same frequency of the LED. After around 7.5 seconds pin 4 of IC2 goes high and IC1D stops the oscillator through D1. If you want to stop counting in advance, push on P2.

Notes:

SW1 can be any type of switch with the desired number of ways. If you want a single fixed timing duration, omit the switch and connect pins 9 & 13 of IC1 to the suitable pin of IC2.
The diagram reset is not immediate. Pushing P2 forces IC2 to oscillate very fast, but it takes some seconds to terminate the counting, especially if a high timer delay was chosen and the pushbutton is operated when the schema was just starting. In order to speed the reset, try lowering the value of R5, but pay attention: too low a value can stop oscillation.
Frequency operation varies with different brand names for IC2. E.g. Motorolas ICs run faster, therefore changing of C1 and/or R3 values may be necessary.
You can also use pins 1, 2, 3 of IC2 to obtain timings of 8, 16 and 32 minutes respectively.
An on-off switch is not provided because when off-state the schema draws no significant current.

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