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  1. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, No, one buffer is likely enough for several filters. Bertus
  2. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, The circuit in the red box, is the circuit to create the REF voltage. On the input of that opamp there is a voltage divider that creates half the powersupply. The opamp is used as buffer. Bertus
  3. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, Yes, The point called REF is the virtual ground. All points called REF are connected together. The ground is lifted to about hlf the powersupply. Bertus
  4. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, The filter circuit can be changed to single supply, using a virtual ground reference: Bertus
  5. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, Yes, That is correct. You can make the LM3914 show voltages between the Rlo voltage and Rhi voltage. Bertus
  6. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, When pin 4 Rlo is 0 Volts and Pin 6 Rhi is 10 Volts, no leds will show with pin 5 at 0 Volts and all leds will show when pin 5 is at 10 Volts. Bertus
  7. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, In the simplest schematic of the datasheet the leds will show from 0 - 1.25 Volt: Bertus
  8. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, You can set the sensitivity of the LM3914 or LM3915 by changing the Rlo (pin 4) and Rhi (pin 6) voltages. The Rlo will set the lowest led and Rhi will set the highest led. Bertus
  9. bertus

    resistor only ring modulator

    Hello, Voltages can not act as diodes. Have a look here about the working of a ring modulator: https://electronicspost.com/ring-modulator-for-the-double-sideband-suppressed-carrier-generation/ Bertus
  10. bertus

    resistor only ring modulator

    Hello, It will not work with resistors only. You will need a non-linear element like a diode in the circuit. That way multiplication will work. Bertus
  11. bertus

    resistor only ring modulator

    Hello, A real ringmodulator consists of two transformers and 4 diodes: https://en.wikipedia.org/wiki/Ring_modulation Bertus
  12. bertus

    Opamp test circuit.

    Hello, Perhaps this page might give you ideas: https://www.pa4tim.nl/?p=4507 And a kind of go-nogo circuit: https://320volt.com/en/operational-amplifier-tester-circuit/ Bertus
  13. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, R1 only sets the ledcurrent. R2 lifts the adj connection to raise the reference voltage: Bertus
  14. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, When pin 8 is gounded the reference voltage will be about 1.25 Volts. When pin8 is lifted with a resistor, the reference voltage will be higher. Have a look at the formulas again. Bertus
  15. bertus

    Opamp test circuit.

    Hello, I would place a voltage divider at the - input of the opamp. It can be that driving opamps to close to the powersupply may distroy the opamp. Bertus
  16. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, The current reference is between pin 7 and 8 of the chips. It can be that pin 8 is grounded, but can also have a resistor to ground. Bertus
  17. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, The led current can be adjusted between 2 and 30 mA. Have a look at these schematics. For the LM3914: For the LM3915: In both schematics there are formulas for setting the led current. Bertus
  18. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, Yes, the (-) goes to the GND and the (+) goes to the MIC. Bertus
  19. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, From the datasheet: Bertus
  20. bertus

    Sallen Key Low Pass Filter, bandpass filter

    Hello, Have a look at fig 8 of the following page: https://sound-au.com/project93.htm It shows the connections on the mic. Bertus
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