Build an Enhanced Simple Bat Detector
The Parts List

The following table lists the parts sources I use for the enhanced Simple Bat Detector. Web sites, mailing addresses, and phone numbers are listed below the table. The total bill of materials is usually less than $35.00.

Ultrasonic Transducer ( 1 ea ) - Notes # 1, 2, 3 Mouser: P/N 255-400SR16-ROX
6.8 mH Ferrite shielded detuning coil - Note # 3 Mouser: P/N 434-02-682J
IC1 & 2 - LM386N-1 - amplifier ( 2 ea ) DigiKey: P/N LM386N-1-ND
IC3 - CD4024 - binary counter ( 1 ea ) DigiKey: 296-2042-5-ND ( Do not substitute this source !! )
Plastic Case with 9 volt battery clip ( 1 ea ) Mouser: P/N 616-61980-510-000
Printed Circuit Board ( 1 ea ) Custom Part - See Note # 4
High Impedance Ceramic Earphone ( 1ea ) Mouser: P/N 25CR035-ROX ( 3.5 mm plug )
3.5 mm 3 conductor Phone Jack ( 1 ea ) Mouser: P/N 161-3402
10 KOhm, PC mount variable resistor ( 1 ea ) Mouser: P/N 531-PT10V-10K
470uf, 16 volt electrolytic capacitor ( 1 ea ) DigiKey: P/N P5141-ND
220uf, 16 volt electrolytic capacitor ( 1 ea ) DigiKey: P/N P5139-ND
10 uf, 25 volt electrolytic capacitor ( 2 ea ) DigiKey: P/N P5148-ND
.047 uf, mylar capacitor ( 1 ea ) DigiKey: P/N P4521-ND or RadioShack: P/N 272-1068
.022 uf, mylar capacitor ( 2 ea ) DigiKey: P/N P4517-ND or RadioShack: P/N 272-1066
220 ohm, 1/8 watt resistor ( 1 ea ) DigiKey: P/N 220EBK-ND
150 ohm, 1/8 watt resistor ( 1 ea ) DigiKey: P/N 150EBK-ND
R2 Gain Resistors - only one is needed - see note # 1

470 ohm, 1/8 watt
1.5 K ohm, 1/8 watt
2.2 K ohm, 1/8 watt

DigiKey: P/N 470EBK-ND
DigiKey: P/N 1.5KEBK-ND
DigiKey: P/N 2.2KEBK-ND


  1. Different ultrasonic transducers require different gain settings, and some times additional components, to make them their most effective in the Simple Bat Detector. The transducer listed above will require a R2 gain resistor that may vary in the range of 470 ohms to 2.2K ohms. I usually suggest 1.5K as a good starting point. If the detector is too noisy, or oscillates, then stepping up to a 2.2K resistor will usually settle it down. If the detector seems to be insensitive to bats that are nearby, a 470 ohm resistor might solve the problem by pushing the gain of the second stage amplifier closer to the limit. One method for setting the gain resistance is to use a 5K ohm potentiometer for R2 to determine the optimum resistor value to use to provide the best gain achievable with your specific bat detector. I have even built detectors with a 5K pot for R2 as a permanent feature sp that the gain could be adjusted in the field.

  2. Most of the low cost transducers available on the market are designed to work at about 40 KHz. Ultrasonic bat sounds can range anywhere from 8 to 120 KHz, so a choice of transducers will involve trade-offs. Detuning the transducer allows more frequencies to be detected, though not as sensitively. Still, the detuning technique makes the Simple Bat Detector fairly versatile. Below is a list of some of the more common North American bats, categorized by thier dominant frequencies, that can be detected with the enhanced version of the Simple Bat Detector.

    25 KHz Big brown bat, Pallid bat, Mexican free-tail
    40 KHz Hoary bat, Mouse eared bats
    50 KHz Western pipistrelle

  3. The Mouser Transducer listed in the parts list should have a 6.8 mH coil wired in parrallel across the back of the transducer for the best possible frequency response for the Simple Bat Detector. Wired in this way, the typical frequency response of the detector will cover 30-50 kHz with an added response node at 20 kHz. Generally, the R1 value for this transducer is 150 ohms. The R2 value will vary from 220 ohms to 2.2K ohms depending on your specific transducer and wiring layout.

  4. In order to promote the availability of the Simple Bat Detector to those who don't have a means of producing printed circuit boards, I have had a number of boards commercially produced. I will pass them on at my cost plus postage. If you would like a printed circuit board, or if you run into difficulty with your bat detector project - email me.

  5. Sources:

Tony Messina - email: - This parts list was last updated on July 10th, 2012