BC557 | Electronic Project Circuits

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Flashing Eyes by BC557

Two-LED-eyes follow the rhythm of music or speech, 3V Battery-operated device suitable for pins or badges
This circuit was purposely designed as a funny Halloween gadget. It should be placed to the rear of a badge or pin bearing a typical Halloween character image, e.g. a pumpkin, skull, black cat, witch, ghost etc. Two LEDs are fixed in place of the eyes of the character and will shine more or less brightly following the rhythm of the music or speech picked-up from surroundings by a small microphone. Two transistors provide the necessary amplification and drive the LEDs.

Parts:
R1 = 10K
R2 = 1M
R3 = 1K
C1 = 4.7uF-25V
C2 = 47uF-25V
D1 = 2mm LED
D2 = 2mm LED
Q1 = BC547
Q2 = BC557
B1 = 3V Battery
SW1 = SPST Switch
MIC1 = Electret Mic

Notes:
* Any general purpose, small signal transistor can be used for Q1 and Q2, but please note that R3 could require adjustment, depending on the gain of Q1. For medium gain transistors, the suggested value should do the job. High gain transistors will require a lower value for R3, i.e. about 390 – 470 Ohm. You can substitute R3 with a 1K Trimmer in order to set precisely the threshold of the circuit.
* Any LED type and color can be used, but small, 2mm diameter, high efficiency LEDs will produce a better effect.
* No limiting resistors are required for D1 and D2 even if this could seem incorrect.
* Stand-by current consumption of the circuit is about 1.5mA.
* Depending on dimensions of your badge, you can choose from a wide variety of battery types:
* 2 x 1.5 V batteries type: AA, AAA, AAAA, button clock-type, photo-camera type & others.
* 2 x 1.4 V mercury batteries, button clock-type.

Source : www.redcircuits.com

Be the first to comment - What do you think? Posted by admin - February 12, 2011 at 11:54 pm

Categories: LED Flasher Tags: BC557, led flashlights

Pulse-Generator & Signal-Tracer with BC547,BC557

Dual-purpose test-instrument Very simple circuitry, 1.5V Battery-operated

This simple circuit generates narrow pulses at about 700-800Hz frequency. The pulses, containing harmonics up to the MHz region, can be injected into audio or radio-frequency stages of amplifiers, receivers and the like for testing purposes. A high-pitched tone can be heard from the speaker of the device under test when all is working properly. The clip must be connected to the ground of the device under test, touching with the probe the different stages of the circuit, starting from the last stage and going up towards the first. When the tone is no longer heard, the defective stage has been found. [...]

Parts:
R1__________________1M 1/4W Resistor
R2,R4_______________2K7 1/4W Resistors
R3________________150K 1/4W Resistor
C1__________________2n2 630V Ceramic or Polyester Capacitor (See Notes)
C2,C3_______________4n7 63V Ceramic or Polyester Capacitors
D1_______________1N4148 75V 150mA Diode
Q1________________BC547 45V 100mA NPN Transistor
Q2________________BC557 45V 100mA PNP Transistor
SW1________________SPST miniature Slider Switch (See Notes)
J1_________________Stereo switched 3mm. Jack socket (See Notes)
Probe______________Metal Probe 3 to 5 cm. long
Clip_______________Miniature Crocodile Clip
B1_________________1.5V Battery (AA or AAA cell etc.)

Read More Source: http://www.redcircuits.com//Page59.htm
Thank you.