Specifications

5.7. CONCLUSION AND RECOMMENDATIONS
5.6.4 Power Consumption
The push-pull RFID reader consumes 420mA (at 12.5V) when transmitting
and the logic consumes 50mA (at 5V) when transmitting, receiving or idling.
Thus, transmitting requires approximately 5.5 Watts and the device consumes
a quiescent power of 0.25 Watts. Tuning of the antenna is crucial to efficient
power usage. The device consumes excessive amounts of power if the antenna
or transformer are incorrectly tuned.
Decoding can require up to 250ms. It will be lower if no tag is detected, as
no further decoding will then take place (see Section 5.5.3 for further details
on the decoding algorithm). In this case, it is possible to trigger another
read almost directly after the previous one and up to four reads per second
can be performed. Thus, if the device is placed in continuous scanning mode
(by holding the trigger pin high), the overall p ower consumption will be
higher if there are no tags present. If there is a tag in range, a full decode is
attempted. The read rate decreases to 2.5 reads per second and the average
power consumption is thus decreased.
For the purposes of this project, the RFID co-ordinator will expressly
trigger reads on either reader. The average power consumption of the reader
is thus determined by the frequency of the read requests.
5.7 Conclusion and Recommendations
The following conclusions and recommendations are drawn from the above
findings:
• Read range is limited by receiver sensitivity. Range improved with
additional receiver gain, even when total gain was high enough to
saturate the amplifiers. It is thus recommended that the highest possible
gain is used (while ensuring that the circuit remains stable and does
not break into oscillation).
• The reader does not perform well in the presence of popular switched-
mode power supplies which operate at frequencies of 33kHz, 65kHz or
130kHz as the harmonics which they produce cause significant interference.
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