This is easy to construct microphone pre-amplifier project using compact electret condenser microphone. The pre-amplifier is important building block of many audio communication systems. Circuit has been built around Op-Amp LM358.
– Power supply : 5 to 12 VDC @ 10 mA
– Output: Gain Approx. 100
– On-Board electret condenser microphone
– Header connector for connecting of power supply input and audio output
– Power-On LED indicator
– Four mounting holes of 3.2 mm each
– PCB dimensions 35 mm x 40 mm
MIC Pre-amplifier - [Link]
If anybody is interesed, I have posed a follow up to this original post with a simple PWM LED driver, adding an ATtiny85 mCU. The post includes schematic, board layout and code for the ATtiny85. I hav tested the circuit up to 22 volts without a current limiting resistor. The FET only needs a small heat sink. Efficiency can be further improved by replacing the LM358 with an RC/LM741. The LM741 has a much sharper rise and fall time than the LM358 when run at 2KHz, resulting in the FET spending less time as a resistor. (during the slow ramp/fall the FET acts as a resistor, generating heat)
PWM Based LED Driver - [Link]
Elmars Ositis has been working on a simple constant current driver:
In my previous post, I slapped together a quick LED lighting solution for my workbench… but it is truly a hack. What I really want to do is make a simple constant current driver, so the power LEDs can be used in other projects. One of those projects is an LED swimming pool light. It needs to be running at maximum brightness and low cost.
After much digging and testing, I found a simple circuit using a power FET, an OP Amp and 0.5 ohm resistor.
This simple circuit accepts a VCC up to 32v (limited by the Op-Amp). The 78L05 regulator provides a stable 5v reference and R1 is a potentiometer serving as a voltage divider, with the output on pin 2 serving as a reference voltage for the basic LM358 Op-Amp.
Simple constant current driver for a high power LED - [Link]
This soldering station controls a 24v 50W solder. Based on ATmega328p microcontroller, with combination of IRL3103 or IRFZ44 MOSFET, 5v 0.5A and 24v 3A power supplies,1500uF 35v capacitor, DS1307 – Real Time Clock, MAX7219 – 4 digit 7 segment LED driver, LEDs and other electronic components. Hakko 936 soldering iron handle with thermocouple control. A LM358 amplifies signal from thermocouple with gain 101.
DIY Soldering Station - [Link]
This is an 125 kHz RFID reader that is based on ATtiny13 micro-controller and an LM358 Operational Amplifier. No special RFID chip is used. The reading, decoding and printing the unique ID from 125 kHz RFID tags is made entirely in software by ATtiny13.
125 kHz RFID reader based on ATtiny13 - [Link]
The circuit uses both op-amps of an LM358 to control the charging of a single cell lithium ion battery. Charging automatically stops when the battery is full, and it is possible to charge batteries that have gone below the undervoltage limit. Power is provided through USB or any other 5V source.
Simple USB DIY Li-ion battery charger - [Link]
When building AVR DDS2 signal generator there were lots of discussions about signal conditioning in analog part of device. First argument was that LM358 wasn’t the best choice for this purpose. Another one pointed to sine wave that weren’t smooth enough.
As you can see there are some dents on it. Other waveforms also are distorted especially when higher voltages are selected. This definitely asks for better analog part. Some people suggested to replace LM358 with OPA2134, but it seems to be quite expensive choice. In my opinion low noise general purpose op-amp can be great too. I’m gonna give a try to Texas Instruments TL074 low noise op-amp. It is low power, high slew rate (13V/us) IC – almost five times faster than LM358 and for same reasonable price.
Modeling of analog part for DDS3 signal generator - [Link]