Joe's Hobby Electronics
  • Joe's Hobby Electronics
    • Electronics Blog

Bat Detector

This is the first project that I've attempted to document for construction on  a breadboard. The documentation tools available aren't brilliant yet, but they are getting better so I thought it was worth giving it a try.

If you haven't yet read Breadboard initial setup, I would go do that now.

At the end of this page, you will find artwork and other files that you can download.

So, first up is the parts list. If you are in the UK, you can get

Qty        Part Number            Description                                            Rapid Part Number
1            C1                           22nF Capacitor                                      08-1065
2            C2, C6                     10uF 25v electrolytic capacitor              11-0220
2            C3, C10                   220uF 35v electrolytic capacitor             11-0260
1            C4                           47nF                                                     08-0237
4            C5, C7, C8, C9         100nF                                                    08-0235
1            R1                           150 ohms (Pack of 100)                          62-0350
3            R2, R5, R6               10 ohms (Pack of 100)                            62-0326
1            R3                           220 ohms (Pack of 100)                          62-0354
1            R4                           2.2K (Pack of 100)                                 62-0378
1            VR1                         5K preset                                              67-0410
3            IC1, IC2, IC4            LM386                                                   82-0266
1            IC3                          CD4020
1            RX1                         40KHz ultrasonic receiver                      35-0180
1            LS1                         8 ohm loudspeaker                                 35-0128
Additional items:
9v battery                      
battery clip                                                                                       18-0080
Breadboard                           840 Tie-Point                                         34-0655

The CD4020 IC is no longer stocked by Rapid Electronics but you will find them for sale with other suppliers or even on Ebay (which may be a good option for a single IC since you typically don't get stung for high postage charges because of minimum order values).
circuitdiagramv1.dch
File Size: 46 kb
File Type: dch
Download File

This is a diptrace format file of the circuit diagram. A free version of diptrace is available here
circuitdiagramv1.jpg
File Size: 95 kb
File Type: jpg
Download File

This is a JPG version of the circuit diagram
batdetector_breadboard.fzz
File Size: 13 kb
File Type: fzz
Download File

This is the breadboard layout source file. You can download free Fritzing software from here
You will notice that the source file contents are slightly different from the picture I've included. This is due to some limitations in the Fritzing software so I can to do a bit of "hacking" of the final image.
bat_breadboard1.jpg
File Size: 249 kb
File Type: jpg
Download File

This is a high-resolution version of the breadboard layout after I've manipulated the image slightly.

Circuit description

The circuit is operated from a 9v battery so make sure that any electrolytic capacitors have a working voltage of at least 10v;16v is better.
Mounting the ultrasonic transducer will probably require you to solder extension wires to the two pins. Likewise with the loudspeaker. 
Bats use ultrasonic frequencies to echo locate and the frequencies vary from species to species. The 40KHz transducer used in this design is reasonably sensitive to the frequencies that most UK bats transmit. That said, the output level from the bats is quite low so to detect them quite a high gain (amplification) is required, so a high gain audio amplifier consisting of ICs 1 & 2 boosts the weak output signal from the transducer.

The first amplifier IC is configured to give a gain of around 20, with the second IC providing a gain of around 10; this gives a combined gain of around 200.

The bats transmit ultrasonic frequencies around 40 KHz, but that's too high a frequency for us humans to hear.
IC3 counts the number of pulses that are received and for every 64th pulse, a pulse is sent to the main audio amplifier; IC4 and this has the affect of dividing down the input frequency.
The audio amplifier IC drives the loudspeaker allowing you to hear an approximation of the ultrasonic sounds the bats are generating.

Breadboard construction

Construction should be straight forward enough. Try and keep link wires as short as possible, and make sure that bare component leads don't touch things they shouldn't. Check the polarity of the electrolytic capacitors; the lead with the vertical stripe is usually the negative.
You may also notice a few slight differences between the photograph of my version of the project, and the breadboard layout image. I made these changes purely to make documenting the breadboard layout clearer for the reader. Electrically they are the same.

Operation and in use

I've had pretty good results with this project, but it requires patience in use. The bats near me have a sixth sense and don't seem to like performing too often when I'm monitoring them. The circuit is also pretty good at picking up other "stuff" going on in the neighbourhood.

If you turn the level of the audio amplifier up via VR1 too high, you can end up with the project producing oscillations or other distortions. You may also find the project picking up radio broadcasts or other local interference from florescent lights or other RF noisy sources.
As a test, try jingling a bunch of keys in front of the transducer and listening to the sounds the project produces. 
© Joe Farr, 2011 - 2020 - Email: HobbyElectronics@kcsl.uk.com