Manual Gain Setting For Op Amp using Digital Potentiometer 

Make sure to measure the resistance and make sure it’s really what the label says because my 103 is actually 104 value.

In about four hours, part two will be uploaded. This time with automatic gain control in addition to the push buttons. I couldn’t stop working on it! And now I can’t sleep.

​@@GadgetReboot I had been wondering if these programmable resistors would exhibit symmetric loads with a small AC signal. Guess so!

My main problem was using an op amp that doesn’t go to the rail but then I used a reference voltage that tried to centre it halfway to the rail so I was biased too far and then it looks a little weird but I was only looking at overall gain and it didn’t matter if the two signals were shifted away from each other‘s center. I need to organize my parts so I can find things immediately when I need them. These were the first op amps that appeared when I was looking.

​@@GadgetReboot You are way beyond me when it comes to the tech matters. My notes on the subject say that TL2272's is a bit better than the LT272's. Something like a TL082 is very fast. Due to the manufacturing process, it is nearly impossible to find an op-amp that is symmetrical rail-to-rail. That 8-pin dual package is seems HIGHLY standard though. Looks like the NE5532P is popular with the audio community. Do you want my code for quick-reading an ATmega328pu? (below) analogeRead() is slow, you know. Even faster for 8-bits. // Porting programs that use the deprecated sbi/cbi macros // Access to the AVR single bit set and clear instructions are provided via the standard C bit manipulation commands. // The sbi and cbi macros are no longer directly supported. sbi (sfr,bit) can be replaced by sfr |= _BV(bit) . // sbi(PORTB, PB1) is now PORTB |= _BV(PB1); // cbi(sfr,bit) is now sfr &= ~(_BV(bit)); #ifndef cbi #define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit)) #endif #ifndef sbi #define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit)) #endif int ADCread10(uint8_t adctouse) { ADMUX = adctouse; // Just the number 0 for A0 sbi(ADMUX, REFS0); // use AVcc as the reference cbi(ADMUX, ADLAR); // clear for 10 bit resolution sbi(ADCSRA, ADEN); // Enable the ADC for ( sbi(ADCSRA,ADSC); ADCSRA & (1

Yeah I’m usually happy if I can get within 0.5 V to the VCC rail but only getting 3.5 out of 5 V is usually annoying. Thanks for the code. I’ve known that analog read function is slow but I haven’t needed too much from it until recently so I need to learn more.

I demonstrated one use in another video where I used the digital pot for auto gain control so the system can automatically scale an input signal. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-4DrT7xwifB0.html Another use would be for remote controlling if the circuit is somewhere else or is otherwise inaccessible but the controller can be accessed somehow and commanded to change the pot maybe over a network or other remote Console.

I scrapped some pin numbers on the white board schematic screen capture just now and put it on Github. github.com/GadgetReboot/Arduino/tree/master/Uno/X9C_OpAmp_Gain_Control

Digital pot + 555 = sound effect generator ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-oFtGOOA25tA.html

@@GadgetReboot Groovy!