Real working bat detector!
My bat detectors will let you listen to bat activity around you. They can hear bats to a distance up to about 100 feet away. They will easily sense bats around you. We use them often at home and while camping or on the water kayaking. I have been making and using bat detectors for more than 6 years. This is my latest version, packaged in a plastic box.
This bat detector is almost exactly like the smaller plastic box bat detector on this website, just a little larger box.
Bats use a remarkable high frequency system called echolocation to hunt for insects in the dark. Echolocation works in a similar way to sonar. Bats make calls as they fly and listen to the returning echoes. A bat can tell how far away something is by how long it takes the sound to return to them. These calls are usually at a frequency too high for humans to hear naturally. This detector digitally divides that high frequency so that humans can hear it. Just set it on a table outside at dusk and listen. In the early evening, you can often see the bats that are detected.
Using the bat detector is easy.
There are two switches and a volume control. One switch controls the power, the other is a dimmer for the LED. Turn the detector on, adjust the volume control, point where you expect bats. It is good to place the detector standing upright on a flat surface. Holding in your hand is OK, but you must keep a firm grip on the detector to avoid making noise. Try it, you will understand. The bat detector will sound best if you keep the volume low, the detector may go into feedback mode if the volume is turned up all the way. Best to start at very low volume, and turn back to low volume when you turn the detector off. Audio from this bat detector is not very loud! It is plenty for a few people together who may be talking but maybe not so good for a large party. You may notice that your detector can hear sounds other than bats. There are insects that will become audible with the detector, as well as man made sounds.
This bat detector is built in an inexpensive plastic box to keep your cost down. Please note that there is a small flaw where the two halves of the box mate together, as shown in one of the photos. I have made other versions in copper and/or glass boxes, they cost $120 - $200 simply because of the packaging. This unit works just as well for less cost!
There is a standard 9 volt battery inside. Battery should last at least 12 hours, up to about 30 hours. Any kind of "9 volt" rechargable battery should work fine. Battery drains more quickly when the detector is making a lot of noise, such as when it is handled.
How does a bat detector work?
This bat detector works by picking up the ultrasonic sounds made by bats (also other creatures and things) via a microphone, the sound then goes through two stages of amplification with a little high pass filtering. The signal then goes to the CD4024 chip which divides the audio by 16 resulting in a sound that can be heard by humans. That signal then goes through a filter to make it sound a bit better and remove some of the high frequency sound to avoid feedback. After that a volume control, then a standard amplifier drives the speaker.