I am modifying 125Khz RFID reader for Proximity card.
The original design of the reader circuit is quite simple, it use CMOS 4069 inverter IC to demodulated the signal to digital.
For the clock 125Khz, it is derived from 8Mhz crystal , and divide down to 125Khz by 74HC393 .
I have success decode the read data using 16F628A.
In order to save the crystal and 74HC393, I like to use 16F628A to generate the 125khz clock as well.
I use hardware PWM to generate 125khz, 50% duty , a nice square wave is generate at pin_b3.
However, when this PWM clock signal is feed to MIC4429 to drive antenna, the RFID detection range reduce by half, compare by using crystal divide clock source.
Also, there is more noice appear on 4069 when using the 16F628A PWM clock source.
Any special requirement for RFID clock? It shall be very straight forward as I think, but the two different clock source signal is given 2 different result.
They look almost identical under osciloscope. I have check grounding and other like decoupling cap, but not helping at all.
The 16F628 is using 4Mhz internal ocsilator. Will this be a problem?
Pls help, I am almost cracy about this problem.
Let me know if you need more info.
Thank you.
The original design of the reader circuit is quite simple, it use CMOS 4069 inverter IC to demodulated the signal to digital.
For the clock 125Khz, it is derived from 8Mhz crystal , and divide down to 125Khz by 74HC393 .
I have success decode the read data using 16F628A.
In order to save the crystal and 74HC393, I like to use 16F628A to generate the 125khz clock as well.
I use hardware PWM to generate 125khz, 50% duty , a nice square wave is generate at pin_b3.
However, when this PWM clock signal is feed to MIC4429 to drive antenna, the RFID detection range reduce by half, compare by using crystal divide clock source.
Also, there is more noice appear on 4069 when using the 16F628A PWM clock source.
Any special requirement for RFID clock? It shall be very straight forward as I think, but the two different clock source signal is given 2 different result.
They look almost identical under osciloscope. I have check grounding and other like decoupling cap, but not helping at all.
The 16F628 is using 4Mhz internal ocsilator. Will this be a problem?
Pls help, I am almost cracy about this problem.
Let me know if you need more info.
Thank you.
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