Bat Detector “BD4066”


25 July, 2007
Revised on 1 March, 2012


It’s been a long time since I first announced tentative version of BD4066. Now, it is my pleasure to announce its release version!

This is a brief translation of my article:
C.Muto, “Making a bat detector,” Eleki-Jack, no.3, pp.165-169, July 2007 (Japanese text).


BD4066 schematic
Fig.1 BD4066 schematic (click picture to view/download PDF version).

Figure 1 shows schematic diagram of BD4066. It is a direct conversion receiver.

Input signal is converted into differential mode and amplified by Q1-Q2 pair and followed by pseud-differential amplifier made of inverters.

U2 configures half section of DBM. Therefore, it is not “doubly balanced” any more :-p).
In this design, LO frequency is about 42[kHz]. If you want to vary LO frequncy, replace 7.5[kΩ] register by series connection of 6.8[kΩ] register and 2[kΩ] pot. The 1000pF capacitor should be temperature insensitive (i.e., CH, CG0 or NP0 is preferable).

Higher frequency components of the mixer output are attenuated by 10kHz LPF and boosted to drive headphone or earphone. The 22mH inductor should be magnetic shielded, otherwise some induction cuases large amount of unexpected noises.
U3, TA7368P/PG has been obsoleted. TDA2822, NJM2073, TDA7233 or MC34119 may be alternative candidates, however, internal circuitry of these devices are absolutely different from TA7368P/PG. Refer to those datasheet for replacement.


Fig.2 BD4066ej (prototype version).

All the prototype circuit including battery box are placed on 72×95[mm] universal breadboard.
In my case, the headphone jack is bonded on the board by using adhesive agent.

The picture on the top of this page is a workshop version, where the breadboard is order-made doubly sided PCB.

Due to higher gain in the front-end section, it is little bit noisy, but we can detect bats’ ultrasonic sound at a distance more than 30[m].
Here is a sample recording of 8 individuals of pipistrellus abramus using BD4066 at Kitakyushu Science and Research Park, Japan on October 2006.

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