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/NOPD-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 ) See Note #5 Below
3.5 mm 3 conductor Phone Jack ( 1 ea ) Mouser: P/N 161-3402-E
10 KOhm, PC mount variable resistor ( 1 ea ) DigiKey P/N 1993-1155-ND
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, capacitor ( 1 ea ) DigiKey: P/N P10963-ND
.022 uf, capacitor ( 2 ea ) DigiKey: P/N P10959-ND
220 ohm, 1/6 watt resistor ( 1 ea ) DigiKey: P/N 220EBK-ND
150 ohm, 1/6 watt resistor ( 1 ea ) DigiKey: P/N 150EBK-ND
R2 Gain Resistors - only one is needed - see note # 1

150 ohm, 1/6 watt

220 ohm, 1/6 watt
470 ohm, 1/6 watt
1.5 K ohm, 1/6 watt
2.2 K ohm, 1/6 watt

DigiKey: P/N 150EBK-ND
DigiKey: P/N 220EBK-ND
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 150 ohms to 1K ohms. For transducers other than the one listed above, 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 so that the gain could be adjusted in the field.

    For the transducer and detuning coil listed above, you may even use a resistor as low as 150 to 220 ohms ... so you may want to start there !
  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 and R2 values for this transducer is 150 ohms, when built on the PC board.

  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 still have a supply of these left, and 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. When my supply is gone, I won't be gertting any more.

  5. Crystal earphones are getting harder to find at large suppliers in the United States. You MUST get high impedance crystal earphone ... it will almost always look big and clunky -- low impedance earphones or earbuds will not work well, if at all. You can sometimes find them on Amazon and eBay - but be sure to look that the earphone has a 3.5mm plug !!

    You should probably try to obtain the crystal earphone first, just to be sure you have a source. I will also try to get a supply on hand, and can add one to your order, at reasonable cost, if you are getting a circuit board from me ...
    email me for more info.



Tony Messina - email: - This parts list was last updated on July, 2022