Crystal quartz oscillator circuit

Another great quartz crystal oscillator schematic with bb139, a 2-nd harmonic quartz crystal and one BF214 transistor. So, the Q quartz is half of the desired transmitter frequency, L1 has 24 turns, 0.08mm ? built on a 455kHz carcase. L2 has 8-9 turns / 0.8mm ? / 5mm ?. Thisquartz oscillator circuithas a great frequency stability, I’ve build it.
Crystal quartz circuit components
R1 = 10K
R2 = 100K
R3 = 8.2K
R4 = R6 = 820
R5 = 15K
C1 = 330nF
C2 = 1nF
C3 = 1.5pF
C4 = 15pF
C5 = 2.2nF
C6 = 6 – 25pF trimmer
C7 = 4.7pF
D1 = BB139
D2 = 5.6v zenner diode
T = BF214
Q = half frequency quartz crystal

Crystal quartz oscillator circuit schematic

78L05 74HC4053D XC95288XL-10PQ208C TL7705ACP TLP521-2 UDN2981A

Sound Activated Switch circuit

With this sound activated switch, control by sound may be very useful, not just on a robot but also for a bit of home automation, for example a sound-activated light responding to a knock on the door or a hand clap. The light will be automatically switched off after a few seconds. An alternative use is burglar protection — if someone wants to open the door or break something the light will come on, suggesting that someone’s at home.
The circuit can work from any 5–12 VDC regulated power supply provided a relay with the suitable coil voltage is used.

When you first connect the supply voltage to thesound activated switchcircuit, the relay will be energised because of the effect of capacitor C2. Allow a few seconds for the relay to be switched off. You can increase or decrease the ‘on’ period by changing the value of C2. A higher value results in a longer ‘on’ period, and vice versa. Do not use a value greater than 47 μ F.

Biasing resistor R1 determines to a large extent the microphone sensitivity. An electret microphone usually has one internal FET inside which requires a bias voltage to operate. The optimum bias level for response to sound has to be found by trial and error. All relevant electrical safety precautions should be observed when connecting mains powered loads to the relay contacts.

Sound activated switch circuit diagram

LM2576T-ADJ DS90LV031ATM AD820AR ADM232LJR ADM705AR BAV70 DG508ACJ EPM7128STC100-10 EPM7064SLC44-10 74HCT14D UC3844N TDA2822M UC3842AN OPA177GS NE558D

50Hz Ripple filter circuit

The ripple filter circuit is specially deisgned to filter out 50 Hz ripple signals from audio lines. A 50 Hz noise is usually found in european countries. In many cases, it is not possible to remove the cause of ripple noise. The featured active filter notch filter solves the problem in suvh cases. It allows the desirable signal to pass through with minimal attenuation. The Q factor of the filter is 10 at the inductivity value of 150 H.

These values can only be achieved practically by using an electronic “coil” such as this circuit. The circuit works as an active RCL circuit. The two opamps Ai and A1 LF356A together with the resistors R2 to R5 , C2 and P1, work as the electronic “coil”. The coils inductivity value is L = R2 x R3 x C1. Potentiometer P1 varies the inductivity value. The filter circuit attenuates the ripple noise by 45 to 50 dB, if properly adjusted.

Ripple filter circuit diagram

Preprogrammed single-chip microcontroller

Twenty-five musical keys and 25 LEDs are provided to denote F to F` with half notes in between. Memory can store a played tune. There are ten preprogrammed tunes (each has an average of 55 note s) masked in the chip. Any tune can be recalled by depressing the Tune Button followed by the corresponding Sharp Key
In learn mode, the player can learn the ten preprogrammed tunes.
 EPF6016QC208-3 AD817AR DG211CJ EPM7192SQC160-10 FDS6612A AD9850BRS AD8016ARB TMS320F2812PGFA PCF8584T SN75176BP PCM1801U PCI9080-3 MAX211ECAI MAX708CSA

Fet Amplifier With Offset Gate Bias Circuit

In this amplifier circuit, the gate of the MPF 102 is biased with an external voltage.
This circuit achieves tighter control of the operating point and biasing conditions.
Source: http://www.hqew.net/circuit-diagram/Fet-Amplifier-With-Offset-Gate-Bias-Circuit_14875.html

Mini Stereo Amplifier Circuit

Using a Thomson TEA2025, this stereo amplifier provides 1 W per charuiel into 4 with a 9-V supply. Input sensitivity is 25 mV p-p for full output.
Note that pins 4, 5, 12, and 13 of TCI should be effectively grounded to a ground plane and heatsinked.

Biquad-audio-filter

This universal filter offers low-pass, high-pass, bandpass, band elimination, and all-pass functions. The Biquad consists of two successive integration stages followed by an inverting stage. The entire group has a feedback loop from the front to the back consisting of Rl which is chiefly responsible for controlling the center frequency, W 0. The first stage of integration is a poor integrator because R2 limits the range of integration. R2 and C form the time constant of the first stage integrator with R3 influencing gain H almost directly.
AD826AR EPM7128SLC84-15 ATMEGA8L-8AU AD9883AKST-110 EPM3032ATC44-10 AD9884AKS-140 DG412DY FDS4435 SP3243ECA SAA7111AHZ SAA7118E The band-pass function is taken after the first stage with the lowpass function taken after the third stage. The remaining filter operations are generated by various combinations of three stages. The Biquad is orthogonally tuned, meaning that W 0, Q, and gain H can all be independently adjusted. The component values known will allow W 0 to range from 40 Hz to 20 kHz. The other component values give an adequate range of operation to allow for virtually universal filtering in the audio region. W 0, Q, and gain H can all be independently adjusted by tuning Rl through R3 in succession.