I’ve built the MK120 minikit successfully and it works as described in the advertising. From the schematic that Velleman published, I understand how the IR pulses on the transmitter are generated, using an astable multivibrator design. On the receiver board side, though, the published schematic shows 4 opamps in succession processing the IR pulses all the way to the buzzer. I get the general theory of how an opamp works, but don’t understand what the four different opamps are doing in the schematic. Could you explain the overall purpose of each opamp in the receiver schematic? I can work out the details once I know how each opamp contributes to the circuit. Thanks! - Don
Sorry, no circuit descriptions.
Basically, IC1A amplifies the signal from the IR receiver 100x
IC1B is an active rectifier, with 100x gain
IC1C compares the output of the active rectifier with a fixed level
IC1D buffers a fixed level to be used as amplifier reference.
That might be enough to puzzle this out. Thanks! - Don
Is the purpose of the IC1A opamp to act as a high-pass filter? Anything lower than the cutoff frequency causes no signal to be passed through to opamp IC1B, correct? If it’s some other type of filter, please let me know so I can continue researching the correct opamp configuration. Thanks - Don
There is no active filtering involved in this project.
This link is to a Yenka simulation you can download and illustrates the opamp’s ability to discriminate a pulsing DC input voltage from a constant DC input voltage and output two different levels of constant DC voltage as a result. It is based on the Velleman PMK120 receiver hobby kit, which monitors a pulsing infrared beam of light. A signal generator is used in place of the pulsing infrared in this schematic to create the input voltage. Change the frequency to see the output voltage switch between two different levels of constant output voltage. Change the positive “reference” input voltage to see how it sets the lower output voltage when the frequency is zero.
http://www.yenka.com/content/item.action?quick=2ag
Yenka is free to download so long as you use it at home.