Friday, May 15, 2015

CD2003 - yet another simple FM radio receiver

In last few days we are looking for some simple FM radio receiver to integrate into one of our ongoing project. For that we try several FM radio receiver ICs including TDA7000, CD2003/TA2003/TA8164, CXA1019 and KA22429. Out of all those chips we select CD2003 (or TA2003/TA8164) based receiver for our project because of its simplicity and outstanding performance. Except to CD2003, Sony CXA1019 also perform well but we drop it because of its higher component count.

We design our receiver based on Toshiba TA2003 datasheet and later we try TA8164 and CD2003 with same circuit. Either CD2003 or TA8164 can directly replace TA2003 IC, and as per our observations TA8164 gives excellent results out of those 3 chips.

Prototype version of CD2003 FM radio receiver

The PCB design and schematic which we used in our prototype project are available to download at elect.wikispaces.com.

Except CD2003 IC, this receiver consist with 12 components. Three inductors used in this receiver are home-produced and all the winding details are available with the schematic diagram. This component count can also reduce by introducing FM band pass filter module to FM RF input stage of TA2003 chip. We try BPW85 FM band pass filter with this circuit and it also give same results as original circuit.

In our testing we operate this receiver using 3.3V power supply and by average it draws 8mA - 12mA current from PSU.

To drive speaker(s), this receiver needs to connect with suitable AF power amplifier and in our testing we use TDA2050 base AF power amplifier with this receiver.

Sunday, May 3, 2015

3A Power supply for USB devices

This is 5V 3A power supply to drive two USB based devices simultaneously. This power supply is design around LM2576-5.0 switching regulator IC and the main reasons to choose this IC is its low parts count, small heat sink requirements and its inbuilt current limit protection feature.

Prototype version of 3A USB power supply

We specially design this power supply to work with development boards / single board computer (SBC) platforms such as Raspberry Pi, Banana Pi, BeagleBone, etc. This power supply can also be used to provide power to USB OTG peripherals over USB Y cables. We test this setup and got successful results with Huawei Ascend P6 mobile phone.

The PCB, schematic diagram and more information about this power supply unit are available at elect.wikispaces.com.

Sunday, April 26, 2015

Low cost DC millivolt source

DC millivolt sources are often used for thermocouple simulations, DMM, ADC and analog circuit calibrations and fault findings, etc. Most of the DC millivolt circuits are based on expensive (and sometimes hard to find) operation amplifier like OP7, LT1077, etc. In this article we introduce low cost DC millivolt source based on commonly available LM308 precision operational amplifier, ICL8069 low voltage reference and 78L05 voltage regulator ICs. This millivolt source is design to obtain 200mV - 700mV DC output with 100Ω impedance. At the time of writing we spend Rs.800.00 (LKR) to complete this project.

Finished view of DC millivolt source.

The most expensive component in this project is Bourns 10K linear multi-turn potentiometer. We use Bourns potentiometer because of its reliability and durability, but any 10K linear multi-turn potentiometers can be used with this circuit.

The output impedance of this millivolt source is set to 100Ω to work with most of the high impedance test instruments.

DC millivolt source with 500mV output.

This unit need external DC power source and we recommend 9V to 25V (100mA) single rail power supply or 9V battery to drive this circuit. This DC millivolt source is easy to build and PCB is the most recommended way to construct this project. All the PCB design files and schematics of this project are available to download at elect.wikispaces.com.

Monday, April 13, 2015

4 way Stereo Unbalanced Distribution Amplifier

This is 4 way stereo unbalanced distribution amplifier (DA), which can be used to distribute (or split) input audio signal to 4 isolated audio devices.

Distribution amplifier in this article is based on commonly available TL072 and TL074 low noise operational amplifier ICs and 7812/7912 voltage regulator ICs. To drive this system, 12V-0-12V or 15V-0-15V 1000mA center tapped step-down transformer is required. Also note that the operational amplifiers used this circuit can be replaced with identical high quality versions like OPA4134, OPA2134, etc. In our prototype we use TL07x series because of its availability and lower price.

PCB design of stereo DA project

To avoid any interference it is highly advisable to construct this circuit on PCB and also use double core screened wires for all external audio connections.

Schematic, PCB and "EAGLE project files" of this project are available to download at elect.wikispaces.com.