Dilshan R Jayakody’s Web Log

TFA9842AJ is quiet old 7.5W audio power amplifier introduced by NXP . This amplifier IC is no longer produced by NXP, but still, it's available to purchase in many places, which including eBay , AliExpress , Amazon , etc. NXP TFA9842AJ Power amplifier IC. I tested a couple of TFA9842AJ based amplifiers in the last couple of years. The main reason I liked TFA9842AJ is its simple, clean design, wide operating voltage, and high-quality bass-rich audio output. Thanks to it's built-in DC volume control circuit this audio amplifier can easily interface with MCU. In this article, we provide a generic TFA9842AJ module which works with most of Arduino boards, MCUs and SOCs. Schematic of the TFA9842AJ module. As illustrated above, this system consists of LM321 operational amplifier and TFA9842AJ IC. To support both 5V and 3.3V logic inputs we introduce logical level selection jumper ( J2 ) into this design. To control the volume PWM input must apply to the J1 . In this...

This is a simple sensor kit to drive 8 active or passive sensors and log its data into a remote Android application. This system also has an option to activate an external device(s) based on the specified threshold of sensor data. This sensor controller is mainly built around the Raspberry Pi Model 3 B+ and PIC16F877A MCU. PIC16F877A MCU is used to interface/select sensors and it's built-in 10bit multi-channel ADC is used to capture the analog signals from sensors. During the prototype stage following sensors are tested with this system: LM35 precision temperature sensor MQ7 Carbon Monoxide gas sensor Electret Microphone NSL-19M51 LDR HC-SR501 PIR sensor A3144 Hall effect sensor Apart from the above list this system can use to drive and capture most of the other analog/digital sensor signals such as current sensors, pressure sensors, chemical sensors, humidity sensors, etc. In this system, Android monitoring application is designed to connect with the sen...

Signal injector and the tracer is a very useful device when troubleshooting electronic audio equipment. We decided to build this signal injector by inspiring the article available in June 2016 - Everyday Practical Electronics (EPE) Magazine ( Audio Signal Injector and Tracer by John Clarke - Page 22 to 29). The signal injector design in EPE magazine is simple but we got few issues while constructing that circuit. The main issue is that LMC6482 is not available to buy in the local market. After few months wait we got a couple of ICs from eBay for LKR 600.00. The second issue is its output is not enough to drive most of the loudspeakers. After prototyping EPE design we decided to build similar sort of signal injector and tracer with commonly available ICs and with more powerful power amplifier stage. For our design, we use the LM358 operational amplifier IC which is commonly available in the local market (for LKR 15 to 20). For the power amplifier, we use LM386 low voltage power...

In this post, we describe the fan controller which we designed for our 9U wall mount server cabinet. This fan controller is designed to drive a 12V DC cooler fan with pre-configured intervals or by monitoring the temperature of the server cabinet. The final version of the fan controller with DC brushless fan and 12V - 60W PSU. Core components of this fan controller are CD4060 binary counter, LM35 temperature sensor, and LM358 operational amplifier. In this design, CD4060 has used as long duration timer and it can be configured to trigger cooler fan from 1-minute and up to 4-hour. In this design, an LM35 temperature sensor is used to activate cooler fan in specified temperature. This sensor stage is useful to drive cooler fan when timer stage is in an inactive state. To control the cooler fan we use AP9971 dual N-channel power MOSFET transistor. We design this system to drive 12V cooler fans up to 2A of current. To test this controller we use commonly available 120mm × 120mm...

When comes to electronic designing and testing, adjustable current sources facilitates to simulate "load" on the circuit(s). The most common use of "constant current source" is to test the performance of power supply units and battery packs. The current source introduced in this article is capable to handle current up to 6A with a maximum input voltage of 50V. This is an operational amplifier based adjustable current source and it uses LM358 in a general voltage follower configuration. To handle large currents we use four 0.1Ω 20W resistors as "load resistor", and those load resistors are drive through pair of 55N06 N-channel MOSFET transistors. Final view of adjustable constant current source prototype. The power supply unit of this project is built around 9V × 2 (2A) step-down transformer and it is designed to get regulated 12V DC voltage. In our design, this 12V power source is used to drive LM358 Op-Amp and 12V cooling fan. In our PCB desig...

Curve tracer is an electronic test instrument to analyze the characteristics of transistors and other discrete semiconductors. In this post we construct USB base curve tracer to analyze properties of NPN transistors. This curve tracer is build around Microchip's PIC18F4550 MCU and it use simple Windows based GUI application to plot captured data of a transistor. In this design PIC18F4550 MCU is used to establish USB connectivity, perform voltage readings and control current/voltage flow into the test subject. To minimize the cost and to make it simple, we use R2R ladder circuit to generate discrete collector-emitter voltage levels for the transistor on test. In each scan session collector-emitter voltage level get increase from 0V to 7.5V in 256 steps. In this design, "tracer" scans the transistor for 7 base current levels which are in between 7µA to 60µA. In viewer application collector-emitter voltage levels are plotted on x-axis and collector current is plotted o...

HAKKO 907 is popular and commonly available soldering iron in the electronics field. To drive those soldering irons user needs to have HAKKO or any other compatible soldering station. The biggest problems with those soldering stations are there higher price tags and limited availability in the local market. Because of those problems, we decided to create our own soldering station, and for that, we choose " Chinese " version of HAKKO 907 soldering handle. Now Chinese versions of 907 compatible irons are available on eBay for less than 5USD. As per our observations, those Chinese versions of soldering irons look and perform almost similar to genuine HAKKO 907 iron(s). To keep it simple we choose LM358 dual operational amplifier IC to monitor the 907's thermocouple and drive the TRIAC. The entire control circuit of this soldering station is powered by single rail 5V DC power supply. To drive both handle and station we use 12V-0-12V 8A step-down transformer. Interna...

Smart Audio Box (SAB) is microprocessor controlled audio switch and amplifier system, which is specifically design for audio composers and for audio engineers. SAB consist of 4 high impedance stereo inputs and two output modes. One output mode can drive stereo headphone/earphone and other output mode can drive pair of 8W speakers. In prototyping stages we identify those modes as " Personal Mode " (headphone output) and " Audience Mode " (power amplifier output). Another main feature of this system is its programmable 16 step attenuation controller. This attenuation controller helps to control the audio output level of each output-mode. Prototyping version of Smart Audio Box The main component of SAB system is ATmega8 MCU, other than that headphone amplifier is design around NJM4556 high current operational amplifier and power amplifier is based on TDA1521A. To operate, this system requires 2 power sources. Microcontroller, ADC interfaces and CMOS logic-s...