Simple doorbell Using UM66

Below is a simple circuit of doorbell using UM66. The circuit can be assembled in a general purpose PCB and enclosed in any toys. 

Parts

C1 - 220 µF 10v
VR1 - 100 k pot
VR2 - 10 k pot
T1 and T2 - BC548
IC1 - UM66

Speaker - 8 ohms
Power - 3v

LED Torch with adjustable brightness

LM3914 is used as the basis of a 10 step variable brightness current-regulated white LED torch. This circuit has only four components in the control and regulation circuit: R1,R2, VR1 and LM3914.

Part List

1. IC - LM3914

2. LED1-10 - 10 white led

3. R1 - 620 ohm

4. R2 - 100 ohm

5. VR1 - 100 k pot

6. C 1 - 10 uf 16 v

7. Power - 3-4.5 volt

8. Suitable cabinet and a general purpose PCB.

Mains Powered LED Lights

Mains powered single LED



Figure1

A single LED can be illuminated by using a 100n or 220n capacitor with a rating of 400v

• The power diode in the first diagram is designed to discharge the 220n during one half of the cycle so that the capacitor will charge during the other half-cycle and deliver energy to the LED. The 1k resistor limits the peak in-rush current when the circuit is first turned on and the main happens to be at a peak.    
• Two LEDs can be driven from the same circuit as one LED will be illuminated during the first half cycle and the other LED will be driven during the second half of the cycle.

Mains Powered Multiple LED's

When 50 to 80 white LEDs are connected in series, a resistor can be used. For 50 white LEDs, use a 4k7 2watt resistor to provide 10mA average current.For 100 white LEDs, use a 2k2 1watt resistor to provide 10mA average current.

Figure 2

The above circuit can be modified with a bridge rectifier to provide DC input to LED. This will prevent from flickering or strobing. 

Mains light with 10 LED

The following circuit illuminates a column of 10 white LEDs. The 10u and 100 R prevents flicker.



Audio Amplifier using LM386

Audio amplifier - LM386

LM386 is a power amplifier designed to be used in low voltage consumer applications. Typical applications are like portable AM/FM amplifier, TV sound systems. It requires minimum external parts and operate from wide range of voltage starting from as low as 4 volt.

Below is the version of the circuit designed by me in one of my projects. It has a Gain of 50 with Bass boost.

Part list

1. C1 - 100 µf 

2. C2 - 10 µf

3. C3 - 0.01 µf

4. C4 - 0.1 µf

5. C5 - 0.01 µf

6. C6 - 220 µf

7. R1 - 10 K

8. R2 - 1.2 K

9. R3 - 10 

10. VR1 - 10 K

11. 9 volt Battery

12. IC - LM386 

C3 and C4 can be replaced by 0.05 or 0.047 µf capacitor. 

This amplifier is ideal for Ipod and cell phones and can be assembled in small box. 

White LED on 1.5 v Supply

2 White LED on 1.5 v Supply

Parts

T1 - BC338

R1 - 2.7 K

C1 - 10 n

D1,D2 - Super bright LED

Transformer - 60 T, 40 T

S1 - On/off Switch

Battery 1.5 V

White LED Flasher

Parts

T1 - BC338

T2 - 2N2222

R1 - 2.7 K

R2 - 47 R

R3 - 330 R - 1K

C1 - 10 n

C2 - 100 

D2 - 1N4148

Battery 1.5 v

1 Watt Audio Amplifier

Audio Amplifier

Parts

Q1 Transistor - MPSW45A
R1- 50 ohms
R2- 10 K
R3,R4 - 100 K

9 volt battery and Speaker

Flashing LED

Alternate red and green flashing LED using 9 volt battery



Part list 

1. R1,R2 - 100 Ohm
2. R3,R4 - 105 K
3. C1,C2 - 10 μF 25 Volt
4. T1-T2 - BC 548
5. D1-D5 - Red LED
6. D6-D10 - Green LED
7. 9 Volt Battery