Electret Mic Stereo Preamplifier

I was looking for a simple per-amplifier circuit. Found one at http://www.minidisc.org/mic_preamp/Simple%20Stereo%20Electret%20Mic%20Preamp.htm. I made minor modifications and here is my version.

Electret mic preamplifier using TL072 (Click on image to view in full size).

Gain is set by R7 and R8 in left channel and R9 and R10 in left channel. In each channel gain will be 1+ (33K/3.3K) = 11.

Replacing 3.3K resistors with 1.5K resistor will increase gain to 23. I tried it but it was too loud.

I build it and it worked great in my testings. You may need to adjust the gain to suit your needs. I used both TL072 and NE5532, both worked same for me, I could not find any difference.

Component List

  • TL072 or NE5532
  • Electret microphone – 2 nos.
  • 10K resistor – 2 nos.
  • 27K resistor – 4 nos.
  • 1uF ceramic capacitor – 4 nos.
  • 2.2pF ceramic capacitor – 2nos.
  • 33K resistor – 2 nos.
  • 3.3K resistor – 2 nos.
  • 15K resistor – 2 nos.
  • 10uF capacitor (ceramic or electrolytic) – 2 nos.

LED Light with CYT1000B

Lighting LED with AC main supply were not that easy. Mainly it required some sort of SMPS with current controlling circuitry. But it is changing. Now there are integrated circuits available specially designed to help to light LEDs with few extra components. One of such IC is CYT1000B.

I like CYT1000B more compared similar ICs in its category because it requires fewer components.

What I most dislike about CYT1000B is that it can only be used drive up to 60mA, thus cannot be used to light most of power LED chips. However, 3528 LEDs are rated 60mA so can be used.

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തെർമോക്കപ്പ്ൾ

ചൂട് അളക്കാനായി ഉപയോഗിക്കുന്ന ഒരു വഴിയാണ് തെർമോക്കപ്പ്ൾ. രണ്ട് വ്യത്യസ്ത ലോഹസങ്കരങ്ങൾ ചേർത്തുണ്ടാക്കുന്ന ലളിതമായ ഒരു ലോഹക്കഷ്ണമോ ദണ്ഡോ ആണിത്. ചൂടിന്റെ അളവനുസരിച്ച് ഇത് വളരെ ചെറിയ അളവിൽ വൈദ്യുതിയുണ്ടാക്കും. അതിന്റെ വോൾട്ടേജ് നില ചൂടിന്‌ ആനുപാതികമായിരിക്കും. ഇങ്ങനെയുണ്ടാകുന്ന വോൾട്ടേജ് നില അളന്ന് അതിൽ നിന്നും ചൂട് എത്രയാണ് എന്ന് കണക്കുകൂട്ടി കണ്ടെത്താൻ കഴിയും.
പക്ഷെ തെർമോക്കപ്പ്ലിന്റെ വോട്ടേജ് നില നേരിട്ട് അളക്കുന്നത് ശരിയായ രീതിയല്ല. കാരണം വളരെ ചെറിയ വോൾട്ടേജായിരിക്കും അത്. ഉദാഹരണം ഒരു K ടൈപ്പ് തെർമോക്കപ്പ്ൾ ഏതാണ് 600 ഡിഗ്രി ചൂടാക്കിയാൽ ഉണ്ടാവുന്നത് ഏതാണ്ട് 20 മില്ലി വോൾട്ട് ആണ്. മിക്ക മൈക്രോകണ്ട്രോളറുകൾക്കും ADC ഐസികൾക്കൂം ഈ കുറഞ്ഞ വോൾട്ടേജ് നില വേർത്തിരിച്ച് അറിയാൻ കഴിയില്ല. എന്നാൽ ഒരു ആമ്പ്ലിഫയർ സർക്യൂട്ട് ഉപയോഗിച്ചാൽ ഈ പ്രശ്നത്തെ മറികടക്കാം. തെർമോക്കപ്പ്ലിന്റെ വോൾട്ടേജ് നില 100 മടങ്ങ് അല്ലെങ്കിൽ അതിൽ കൂടുതലോ ആയി ഉയർത്തി മൈക്രോകണ്ട്രോളറിന് നൽകാം.

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Nginx Configuration for WordPress with HTTPS Enabled

Few days back I switched back to WordPress from static site generator Hugo. On my server I am using Nginx as web-server though I am more familiar with Apache Web Server (Now I can’t remember exactly why I switched to Nginx?!). I am using LetsEncrypt SSL certificates and always redirect regular HTTP traffic to HTTPS.

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Thermocouple Amplifier with OP07C Op-Amp

Recently I created a soldering station based on Arduino Pro mini. It involves reading temperature data from thermocouple within soldering iron. Thermocouple produce a very little voltage, around up to 30 Milli volts for soldering irons. So, soldering station uses an op-amp based circuit to amplify those small signals from thermocouple to signal high enough for microcontroller’s ADC channel can detect. I noticed many DIY makers on Internet uses LM358 as the op-amp for those amplifier circuit, while researching on the topic. I learned LM358 is not a good choice for the purpose because it has relatively high off-set voltage, a voltage op-amp gives in output when input voltage is 0. Then I researched many many designs and finally settled to use OP07C op-amp IC.

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PWM with STM8S

PWM is a great way to control brightness of LEDs, speed of motors, etc. Most microcontrollers including STM8S has built in ability to generate PWM signals. In this article I share simple code to generate PWM signal in STM8S microcontroller. However, I don’t write anything about PWM theory other than basic calculation to get required frequency and duty cycle.

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Bootloader-less Programming Arduino Pro Mini

Recently I was creating a configurable timer circuit based Arduino Pro Mini. The circuit has a momentary push button which user can press to turn ON the device. The device will turn OFF itself once the time is elapsed. On starting, Arduino has to turn on a relay to get permanent connection to power source, so it will get power when user released the push button. One issue I faced was that Arduino takes around 3 seconds to start executing the program because of the presence of the bootloader. So, user would have to keep push button pressed for around 3 seconds to get the device started. I wanted to get rid of bootloader so Arduino will start executing the program soon we press the push button for a moment.

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STM8S: Timer 2 with Overflow Interrupt

In previous post I showed how we can use Timer 2 as simple counter. In this post I am going to show how we can program to have interrupt when its value overflow. As simple experiment, we will toggle an LED in each second within the interrupt handler (also called ISR, Interrupt Service Routine).

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STM8S: Use Timer 2 as Simple Counter to Blink LED (without Interrupt)

Timers inside MCUs are very useful and essential peripherals for timing applications. In this article I will show Timer 2 in an STM8S (specifically STM8S103F3) can be used to blink an LED.

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