The variation of coil voltage controlled by the modulation transistor results in a perturbation of voltage in reader antenna coil. The tuning compensates the variations in the component values and the perturbation of coil inductance due to environment effect. Tolerance of the carrier frequency: 13. Class 4 Active read-write tags with integrated transmitters that can communicate with other tags and readers. The maximum range of the proximity card reader is about 1. This signal is used as a clock for D flip-flop U6:A for which the D input is a reference 62. Equation 38 is recommended if it needs very accurate calculation while Equation 30 gives quick answers within about 10 percent of error.
In the future, this technology is proving to be a major disruptor for the retail shopping experience with concepts like. Of course many other items, but they are purely derivative from the two I mentioned first. Only 25 tags can be in the reader's field at any time, and the application involves water and chemicals, but no metal. The tuning compensates the variations in the component values and the perturbation of coil inductance due to environment effect. Specifically in access control and animal tracking applications.
This example does not specify read speed. For example, a circuit with Q of 40 can have a coil voltage that is 40 times higher than input signal. It has maximum amplitude in the plane of the loop and directly proportional to both the current and the number of turns, N. As a result, the amplitude of the antenna coil voltage varies with the modulation signal. In b , the impedance curve has a peak at the resonance frequency.
Error Conditions If the host computer does not send programming data to the programmer for more than 3 seconds, the programmer will time out and reset. In the programming modes, each individual bit is addressed serially from bit 1 to bit 128. This is referred to as a collision. The tuning compensates the variations in the component values and the perturbation of coil inductance due to environment effect. Figure 5-1 shows the anti-collision flow chart.
For links to the neccessary data-sheets please click the links on the respective component. After constructing the coil, we proceeded to tune it by removing coils until we saw the highest resonant voltage from our carrier frequency, which was at roughly 88 turns. This is often called backscattering. The programmer reports to the host computer the status of the programming. After the 5 bit times, the device sends data. The voltage drop in theantenna coil is a summation superposition of transmitting signal and backscattering signal. If the tag receives processing and writing com- mands along with block data, it writes the block data into the specified memory block, and trans- mits the written block data for verification.
If the environmental conditions would allow, you could use a less expensive label-type tag. Conductive inks have much higher resistance and, therefore, low Q. In other words, doubling the tag's coil diameter may double read range to as much as twice the reader's antenna diameter, as noted previously, as long as Q and conductor surface area remain relatively constant. In this case you choose the inductor's dimensions before you choose the capacitor. With this in mind, we wondered whether a group of 5 or 6 bits possibly represents a single bit.
For example, the signal level at 30 meters away from the device must not exceed: 2. This function loops until it finds the start sequence and stores it in a global variable and calculates the end sequence. Battery-assisted units, which are not particularly common outside of key fobs, may do some energy harvesting but require some source of power. This results in a phase-shift in the 62. In that case, however, the read-range requirement would have to decrease because a low Q would be mandatory. Table 1 shows the characteristic of each frequency bands.
Through much research and testing, we were able to develop a system which not only met our preliminary goals, but even met some of our more ambitious goals, such as remote administration for adding codes to the code database. This configuration controls C2 for tuned and detuned frequencies. This is best to use when tag orientation is unknown, but you lose at least 3dB when compared to a linear polarized antenna. Step to Design an Antenna 1. The modulation transistor damps or undamps the coil voltage when it sends data. The magnetic flux Ψ in Equation 4 is the total magnetic field B that is passing through the entire surface of the antenna coil, and found by: The maximum magnetic flux that is passing through the tag coil is obtained when the two coils reader coil and tag coil are placed in parallel with respect to each other.
Read-only devices typically can store a 64- or 80-bit unique number that is written by the factory. Note that Equation 4 does not calculate Q for coil and capacitor values, because resistivity, which controls Q, is independent of the reactive parameters in the tuning equations. The mutual inductance between two parallel conductors is a function of the length of the conductors and of the geometric mean distance between them. The latency is due to the redundant code check. Data decoding for the received signal is accomplished using a microcontroller.