Technical data

Please be aware that this is preliminary data, so changes can occur anytime until the product is finally shipped.

The Standard Horchbox

Basic principle

The basic principle of the Horchbox is quite simple. Using a ultrasonic microphone the calls from bats are converted from air pressure changes to electrical signals. They are amplified, digitized and written to an digital storage medium, which is a SD-Card.

The recording of the bat calls is automatically started. Different algorithms can be chosen to cope with different environmental conditions.

Additionally the box incorporates a real time clock, so whenever a recording is done, the date and time information is also stored on the SD-card. There are also a light sensor and a temperature sensor included, so these information is also stored on the card.

Moreover, the box does not only record the bat calls, but also the above mentioned environmental data, even when no bat call recordings are done. This recording is done using a slow sample rate, so the storage capacity is reduced only very little. The environmental data includes temperature, ambient light, voltage of battery and to some extend microphone information.

The Horchbox is power supplied by a battery located inside the box, so the housing has only got two outer parts: The microphone and the light sensor.

Microphone and recording

The microphone is a special ultrasonic microphone, with a good performance up to 60 kHz. It will also work in the range between 60 kHz and 100 kHz, but the sensibility is reduced.

The recording is done without any compression, directly on the SD-card. The sampling rate is 200 kHz using 16 Bit, so each second of recording uses 400 kByte on the storage device. If necessary you can choose a higher samplerate of 300 kHz to record also bats up to 150 kHz frequency.

The duration of the recording can be configured to any amount of seconds up to 11, by default 1 second is used. After 11 seconds the box will make a real short stop (less than 0,1 second) and after the it is ready to record again. You can also use the 'prolongation mode', where the box extends the recording as long as bats are present.

Using the light sensor the user can select a threshold value, above which no recordings should be done. This helps to avoid a lot of recordings at day time, when no bats are around. Additionally the box can be controlled on a clock basis, for example 'do no recording between 9am 7pm'.


Any SD-card up to 2 GByte should be OK at the moment, which is not an SDHC card. Support for SDHC will be added later for free, this needs only a SW update. The Horchbox can be ordered along with SD-cards with sizes 2 GByte which have been tested with the box to avoid any compatibility problems.

With 2 GByte cards the amount will be about 1000 recordings of 5 seconds.


There will be different battery options for the box, in principle all batteries are OK as long as they provide a voltage between 6 Volt and 9 Volt. Higher voltages than 9 Volt can destroy the box - please remember this, if you would like to use other batteries.

The power consumption of the box is lower than 50 mA, depending on the state of activation (sleep, idle, recording).

The typical battery sold with the Horchbox is a 2400 mAh battery, by using sleep modes the box can run between 5 to 10 days.

All battery life times are estimation at the moment.