I have setup this EM4095 with my arduino and everytime I run an oscilloscope on it for some odd reason it transmits at 60 khz when it is supposed to be 125 khz. The circuit i use is below and for the antenna I made a loop antenna at 450 uH. Anyone know what the problem may be?
I moved your topic to an appropriate forum category @watchittoughguy.
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Thanks in advance for your cooperation.
How are you powering it? Post a link to the source.
I am powering it with 5 volts pin from arduino uno
Yes. Your scope probes are shorting the antenna circuit. You gave no clue where you placed the probe and the probe ground connection.
The LC circuit with the 450uH coil and the two 1n8 caps (3n6) should indeed resonate at about 125kHz. Unless the parts values are not what you think they are.
Show us more (images).
The 60pF capacitance of a scope probe can indeed de-tune the coil, but not significantly.
C7,8,9 are critical.
How do you know that the inductance of the coil that you made is 450μH?
Is this just a calculated value, or have you measured it somehow?
I used the wheelers formula.
The most likely culprits are incorrectly constructed coil and/or incorrect capacitor values.
check first:
Put a scope on VDD at the EM4095 and at the processor while transmitting. If VDD dips or has large 125 kHz ripple, add local bypassing: 0.1 uF ceramic close to the IC, plus 10 uF to 100 uF nearby.
Check antenna tuning. If the coil/capacitor network is badly tuned, the driver current and waveform can be poor. That can reduce field strength and cause marginal tag communication.
Separate the EM4095 supply from the processor supply with a small resistor or ferrite bead, then add local capacitance at the EM4095 side.
Keep the antenna loop wiring away from processor reset, clock, serial, and analog lines.
Check the modulation waveform with a scope. If the carrier is collapsing or distorted during modulation, the reader may only send part of the command correctly.
Also check software timing. With 125 kHz RFID parts, marginal timing or interrupt delays can look like incomplete transmissions.
My first suspicion would be supply dip/ripple or poor antenna tuning.
- Place a 0.1 uF ceramic directly at the VDD pin.
- Add a nearby bulk capacitor (10-100 uF).
- Check the supply voltage with an oscilloscope while transmitting.
- Verify the antenna is tuned correctly to 125 kHz.
- Measure current with and without the antenna connected.
If you are powering it from a weak LDO or a high-impedance source, such as an Arduino the transmit current can cause momentary supply dips that may reset a microcontroller or introduce noise into analog measurements. Try an external more robust power supply.
I figured it out. I had to remake an antenna turns out the one I was using wasn't that good maybe did to many or too little loops. All resonated now. ;D
Too many turns if the frequency was too low.
Yeah you're right.