Digital Telemeter FAQ

Q: How many channels does the DT have?
A: The maximum number of transmitted data channels, the resolution of the digitized data, and the sampling frequency of the transmitted data combine to determine the data throughput of the DT. The recording configurations of the DT are thus constrained because the throughput is determined by the fixed capacity of the wireless digital link. The following table shows the channel number, data resolution and sampling frequency of various DT configurations.

Q: What kind of signals can be recorded with the DT?
A: Basically any biological signal can be acquired by DT because it makes wideband recordings. Even if the main purpose of the DT is to record brain signals (action and field potentials), you are free to record other biological signals such as EP, ECG, EMG etc.

Q: What is the DT’s bandwidth?
A: DT acquires wideband data with a highpass frequency of 1Hz. Typically the lowpass frequency is set to 12kHz because the fastest neural signals are action potentials with maximal waveform frequency components < 6 kHz.

Q: Does the system work for mice or smaller subjects?
A: The main constraint here is the mass of the battery. We anticipate a small version with a limited number of channels around Q3/2007.

Q: What are the dimensions of the DT?
A: The dimensions of the transmitter are 23 x 35 x 7.5mm. In the following picture you may compare the size of the transmitter with a US 25 cent coin and a 2 hour button-type battery. The device is covered with heat-shrink tubing for lightweight protection.

Q: What is the DT weight?
A: The transmitter weighs 8 grams. One must also consider the mass of the battery, which depends on your experimental needs. For example, a rechargeable button-type battery for 2 hours of recording (shown in the picture above) is another 8 grams. A battery for a 6 hour recording weighs about 19 grams.

Q: How long can the DT operate with the battery
A: Transmitter consumption is 120mA, which means, that with the battery shown in the picture above (240mAh) the DT will operate for 2 hours. The longer the recording time, the larger the battery. For recordings of unlimited duration, you can also use the DT with a two wire supply.

Q: What is the maximum distance at which the DT can operate?
A: Errorless transmission with 100% of transmitter data was tested at maximum distances of 8 meters.

Q: What kind of connector does the DT use to connect to the electrodes?
A: The standard connector we use is the Mill-Max double-row connector with 50mil spacing. We also support Omnetics connectors, and can customize the DT to fit most connectors.

Q: Does BSG provide electrodes and electrode microdrives?
A: We can provide microdrives with the DT. We collectively have decades of experience with extracellular electrodes and are happy to provide consultation on where to purchase and/or how to make electrodes.

Q: Can I use my existing analog data acquisition system with the DT?
A: Absolutely. The Transmitter sends data wirelessly in a digital form to the Receiver. The Receiver processes the digital data and may convert them back to the continuous analog signals that appeared at the electrodes with an adjustable gain so the output is in the range of 1 V. The signals can then be viewed on a standard oscilloscope or recorded by a conventional analog data acquisition system (see the following picture) without the need for additional amplification.
However, the main advantage of DT is it is fully digital which allows the user to store the digital data exactly as they were acquired by the transmitter. This is done through an additional Digital Acquisition Unit and the USB port of a laptop or PC. In this case, the data are digitized just once – at the Transmitter and then they are transmitted, processed and stored in the same form. If you use a conventional data acquisition system interfaced to the DT Receiver’s analog outputs, then the data that are transmitted data in a digital form need to be converted back to analog and then converted once again to digital signals, which can be stored in the computer.

Note : click on the image for larger view

Q: What if I don’t have a recording system?
A: In this case, you have two options which both allow you to take advantage of the progressive, fully digital mode of the DT system. For our first option, we offer an eight channel stand-alone version of the DT which includes a recording system in its receiver and plugs directly into a laptop via USB. For our second option, if you require a more sophisticated recording system, you can use the Digital Transmitter, Digital Receiver and a Digital Acquisition Unit by the company Axona. The Axona dacqUSB system is fully integrated with the DT, and has many advanced features. Perhaps most importantly, it can run on a laptop and so combined with DT it is easily portable. For more information please visit the Axona website.

Q: What is the difference between an analog and a digital recording system?
A: Today, several companies offer wireless recording systems, which work on the basis of analog data transmission. In these cases, analog biological signals are multiplexed into a single analog signal and then transmitted in this analog form to the receiver. At the receiver they are demultiplexed. To store the data the demultiplexed signals are processed by a conventional recording system which amplifies, and filter, then digitizes and stores the digital data on a computer. In contrast, the digital system of the DT converts the wideband analog biological signals into digital data on the subject. The digital data are serialized (copied onto one serial data channel), transmitted and stored exactly as they were acquired. The main disadvantage of analog transmission is that any fading of the signal between transmitter and receiver will impact (corrupt) the recorded signal amplitudes and frequencies. The undesirable consequence of this is the hard to avoid misinterpretation of biological signals. By digitizing the signals at the electrode interface, before serializing and transmitting them, DT is able to virtually eliminate the possibility of such misinterpretation, because a large amplitude digital signal is transferred and checked for errors using exhaustive error detection mechanisms. If a transmission error is detected the data can be resent. If due to repeated transmission failure uncorrupted data cannot be received, then no data (flatline) are output by the receiver. When analog signals are transmitted, the signals are received continuously and without recording in parallel with wires, it is virtually impossible to determine whether the signal at the reciever was corrupted or whether it accurately represents the biological signal.
A commonly used example to illustrate the difference between the digital and analog signals may be helpful. If you play your favourite music from your old vinyl, where the music is stored in an analog form, all the scratches are heard from the speakers and can’t be easily separated from the music that was actually recorded. In contrast, if you have the same recording on a CD and you play that music, if there are scratches on the disc that are too big so that data can’t be reconstructed using digital correcting mechanisms, you just don’t hear anything. One can say that in the example with music, it is probably better to hear something, even with the clicks caused by scratches, but for accurate biological recordings, fidelity is essential.

Q: What are the advantages of wireless recording?
A: The main advantage is that the recorded subjects are free to move, which allows the experimenter to use complex mazes with multiple levels or large open fields. Wireless transmission also replaces the use of expensive and hard to move swivels for conducting electrical signals. Finally, wireless recording offers great portability, because if you want to switch the experiment, you only move the subject with the transmitter in comparison to moving all the cabling and other installations. This also minimizes the cost of whole the system, in particular since DT also replaces the main amplifiers needed for conventional analog recording.