Bat scanner
From Eric
Contents |
Micro amplifier
Mixer
Frequency generator
To generate the local frequency, I use the Arduino's "Tone" function. I have also tried to use directly the chip's timers, but this doesn't work much better because the control on the frequency (using the timer registers) is too coarse. To make iot work correctly, I would have to generate a very high base frequency and use another level of (software) counter to decide when to toggle the output. This is basically what "tone" does.
Filter
I use an active Sallen-Key second order filter.
From split supply to mono supply
In my initial configuration, I used a dual [-12v,12v] power suply from mains, but this is not very practical if I want the device to be portable.
For info., here is a classical way to build such a symmetric power supply (from https://circuitdigest.com/electronic-circuits/12v-dual-power-supply-circuit)
So, I have to create my symmetric [-5v,+5v] power supply. The first solution could be to use two batteries (e.g., two 4.5V batteries).
Another solution is to use a single source (e.g. 12v) and create two 6V outputs out of it using a resistor divider, buffer it using a unit gain follower op amp, "inject" the signal of interest on this source using a cap, and use another op amp to do the filtering (see above).
But, finally, since I am not amplifying a real audio sound, I am going to use a single power supply and simply ignore the negative part of the signal. That'll be just fine.
