Sunday, February 7, 2016

Musical trees

"Musical trees" is a part of creative arts installation and this project is capable to produce different audio tones by detecting human touch to its attached plants. Existing version of this driver is capable to monitor 8 plants and produce different sounds for each plant.

Prototype version of "Magic Tree" project with 2 plant samples.

This project is build around PIC16F628A 8-bit microcontroller and PT2399 echo processor IC. To drive the sensor electrodes we use pair of CD4011 quad 2-input NAND gate ICs. This prototype use TDA7052 1W audio amplifier IC to drive the speaker(s).

The existing firmware of PIC16F628A is designed to produce tones in between 155Hz to 1244Hz and this range can be change by modifying the supplied firmware source code. In this design PT2399 echo processor IC is used to get more natural (/ deep) sound effect by adding some reverberation to the output.

Schematic and firmware of this project is available to download at

Saturday, January 16, 2016

Victor SEA-50 graphic equalizer restoration

Few weeks back I got Victor SEA-50 stereo graphic equalizer from one of my friend. This is 10 band stereo graphic equalizer manufactured by Victor Company of Japan (now JVC Kenwood) around 1970 - 1980. SEA-50 consist with 63 transistors and it provides ±12dB control range for 32 Hz, 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, 12 kHz / 16 kHz / 20 kHz center frequencies.

The SEA-50 which we got is not working properly and most of its controls may generate distortion above +8dB and below -8dB. Apart from that left channel of this receiver has low volume and distortion.

Defective transistors in control board (next to 2SA493).

After few hours of checkup we identify few defective transistors (2SC982) in control board and we replace those with 2N3904 NPN transistors. Subsequent to this fix, all controls of SEA-50 start to work again on its full range (±12dB) by without producing any distortion or clipping.

Sunday, January 10, 2016

Mullard 3-3 Amplifier Project (Part 1)

Mullard 3-3 is quiet popular 3W tube amplifier introduced by Mullard Ltd in 1956. A schematic and design detail of this amplifier is available in "Mullard Circuits for Audio Amplifiers" book and in National Valve Museum article. This amplifier is based on EF86, EL84 vacuum tubes and EZ80 full wave rectifier tube. In this project we decided to construct this original Mullard 3-3 Amplifier with some slight changes and commonly available electronic components.

Top view of Mullard 3-3 amplifier with 6P14P and 6J8 tubes.

In our prototype we replace EZ80 tube with 400V 5A bridge rectifier which is commonly available in many electronic spare parts shops. Also we replace EL84 with 6P14P pentode and EF86 with 6J8 pentode. Both of these valves can directly use with this circuit and those values are available for lesser price than EL84, EF86 tubes.

Monday, December 28, 2015

Light operated voice messenger

This is simple electronic project which we implemented for some local event to guide audience automatically with some prerecorded voice messages. The core component of this unit is ISD1820PY voice record/playback chip which is manufactured by Nuvoton Technologies. Except to ISD1820PY, this unit use commonly available low power LASER and LDR assembly to detect people. To drive the loudspeaker we use popular LM386 audio power amplifier.

Basic setup of electronic voice messenger.

Thanks to ISD1820PY and LM386 this system can implemented on breadboard or on strip-board with minimum number of external components. This circuit is designed to drive using 6V or 9V DC battery but it can also drive with 6V or 9V DC regulated power supply. To get 3.3V we use LD1117V33 voltage regulator, but this can also be replaced with some commonly available 3.3V regulators such as LD33V, MC33269-3.3, etc. For the speaker we use 4-inch 8Ω full-range speaker.

Prototype version of electronic voice messenger.

This unit can used with both dynamic and condenser microphones but according to our experiments, ISD1820PY produces excellent results with dynamic microphones. As per our observation with some condenser microphones results are not up to the satisfactory level.

Detailed schematic of this project is available to download at