Thursday, November 14, 2013

Flashing Eyes

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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.
Circuit Diagram:

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

  • 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

3x3x3 LED Cube Circuit Diagram

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This circuit drives a 3x3x3 cube consisting of 27 white LEDs. The 4020 IC is a 14 stage binary counter and we have used 9 outputs. Each output drives 3 white LEDs in series and we have omitted a dropper resistor as the chip can only deliver a maximum of 15mA per output. The 4020 produces 512 different patterns before the sequence repeats and you have to build the project to see the effects it produces on the 3D cube.

Circuit diagram

12V Flourescent Lamp Inverter

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Fluorescent tubes use far less energy than incandescent lamps and fluorescent tubes last a great deal longer as well. Other advantages are diffuse, glare-free lighting and low heat output. For these reasons, fluorescent lighting is the natural choice in commercial and retail buildings, workshops and factories. For battery-powered lighting, fluorescent lights are also the first choice because of their high efficiency. The main drawback with running fluorescent lights from battery power is that an inverter is required to drive the tubes.

Circuit diagram:

12V Fluorescent Lamp Inverter Circuit Diagram
Fig.1: two switch-mode circuits are involved here: the DC-DC inverter involving IC1, Q1 & Q2 and the fluoro tube driver which converts high voltage DC to AC via IC3 and Q3 & Q4 in a totem-pole circuit.

Inverter efficiency then becomes the major issue. There are many commercial 12V-operated fluorescent lamps available which use 15W and 20W tubes. However, it is rare to see one which drives them to full brilliance. For example, a typical commercial dual 20W fluorescent lamp operating from 12V draws 980mA or 11.8W. Ignoring losses in the fluorescent tube driver itself, it means that each tube is only supplied with 5.9W of power which is considerably less than their 20W rating. So while the lamps do use 20W tubes, the light output is well below par.

This circuit generates in excess of 300V DC which could be lethal. Construction should only be attempted by those experienced with mains-level voltages and safety procedures

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