Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

RFID proximity security

Status
Not open for further replies.
The document you attached is one of the best descriptions I have read - it would be difficult to do better.

I think pages 131- through 134 contain what you're looking for. It requires a strong background in encoding methods, which you can probably get a start from AN680.
 
Receiver section

The document you attached is one of the best descriptions I have read - it would be difficult to do better.

I think pages 131- through 134 contain what you're looking for. It requires a strong background in encoding methods, which you can probably get a start from AN680.


Thanks....but the the guide doesn't explain the circuit diagram in detail. For example, in the receiver part, the opamps are used for demodulation of ASK. What is the role of those opamp circuits ?

**broken link removed**
 
The diode D9 detects the carrier, providing a varying voltage that follows the carrier amplitude. C15 and C16 remove as much of the carrier as possible. C13 and R19 form a high pass filter against the virtual ground at pin 6 of U5B. U5B has a high gain due to R19 and R22. But it's clipped at the forward conduction levels of D7 and D8 (so it's a square wave from +4.35 to +5.65V). U5C has a gain of about 5, with a centerline of 5V, which makes it as close to rail-rail as the TL074 can do. C11 limits the bandwidth. R23 and C17 are yet another low pass filter, I don't know why. U5D is used as a comparator with hysteresis, to give nice square waves to the PIC. R20 and R25 reduce the 9V signal down to about 5V logic level.

I leave it to you to calculate all the time constants.
 
Once i filter the data using RC filters, i pass it through opamp comparator for wave shaping. The output of opamp is 24V peak to peak(+12v to -12v with a centreline of 0, i.e. VDD=+12v and Vss= -12). I attenuate it to 10 V pk to pk (5v to -5 v) using voltage divider resistors R12 & R13. Then i clip the negative part using diode D6. Ideally, this arrangement should give me an output across R14 that varies from 0 to 5v( TTL levels for microcontroller).
But in reality, the output is not clipped, that is, it's still a signal varying from 5v to -5v(10v pk to pk). Can u tell me why??


**broken link removed**

Is there any other way of getting 24v(-12 to +12v) signal to TTL level??
 
Your paragraph does not describe the same circuit as in your schematic. Are you using a simulator that ignores the supply voltages?

There is no way that a 741 op amp with 0V and 9V as supplies can output 24V pk-pk.

Epic Fail.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top