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

Monday, December 21, 2015

74181 ALU design on Altera MAX II CPLD

74181 is 4-bit arithmetic and logic unit introduced by Texas Instruments in March 1970 and it is known for being the first ALU in single package. This chip is no longer in manufacturing but still it is quite popular in CA (computer architecture) courses in many colleges.

To test the behavior of this 4-bit ALU we decided to construct it on Altera MAX II CPLD. For this project we choose EPM240T100C5 CPLD and logic design is implement using Altera Quartus II. For logic design we refer Fairchild Semiconductor’s DM74LS181 datasheet. This setup is tested on basic EPM240 series development board with some mechanical switches and couple of LEDs.

74181 4-bit ALU test setup with EPM240T100C5 development board.

There are several test circuits available for 74181 ALU and our test setup is partially based on Electronics for Your (EFY) 1997 article. In another test setup we use HEF4040 to drive, A and B operands of this ALU.

The test setup attached into this article is the minimum configuration which anyone can build with small number of commonly available electronic components.

All the downloadable content related to this project are available at

Friday, December 18, 2015

Replacement LED driver for AN6877

AN6877 is linear AF level meter IC produced by Panasonic and it is commonly found on many audio equipment. This chip is no longer manufactured by Panasonic and finding replacement chip for AN6877 is also quiet difficult.

The circuit described in this article is design to replace AN6877 base LED drivers and it is based on commonly available components. This replacement LED driver is design using 10, MMBT3904/2N3904 transistors and it can easily modify to get necessary number of outputs.

SMD version of PCB design for 8-dot driver.

During the prototyping stages we test this driver with minimum of 7 LEDs (AN6877 configuration) and up to 12 LEDs. This LED driver is design to work with 9V to 12V DC power source.

With 7 LEDs and 9V power source, this module can directly replace AN6877 base LED driver modules.

Schematic and PCB design related to this LED driver is available at