This is very strange. I can’t think of any reason why this would happen.
I’m hacking my electronic dog door to use RFID instead of the buggy ultrasound it’s using now. For this I need a fair read range on the dogtag type RFID tag. I figured I need about 4 to 6 inches (10-15 cm) of reliable read range to make sure the dog isn’t there scratching at the door unable to get in.
My setup is the ardunio nano and RFID reader from Priority 1 in Australia and a 16cm loop antenna also from them.
When I have the nano plugged in to the Mac’s USB port and getting power from that, I’m able to get a read range of between 13-14cm. Pretty darn good and I think I’m ready to work on the install.
But when I detach the nano’s usb and plug it in to a 5v power supply (+5v at VIN), the read range drops down to 6cm and sometimes a lot lower.
When I have the nano plugged in to the Mac’s USB port and also plugged in to 5v power, I see the Mac USB amp load drop to 0 - so it should be getting power from external, but is still connected to serial. Like that I get the bigger read range.
If I plug the nano usb into a usb wall wart power supply the range is dropped down.
This rfid reader can work without the arduino and tell me when it reads. And without the arduino at all it’s also short range.
Something else must be going on in the USB connection to a mac that’s different than when it’s unplugged from the mac… something that isn’t about the power. But what? And why would it effect my read range?
My next test was powering the rfid reader with the 5v supply and the arduino with the mac’s usb, but have common gnd. With the rfid reader connected to the same gnd as the usb we have a longer range again of about 10-12cm.
Is my issue still just bad power coming from the external power supply? Should I be using some sort of cleaner power conditioner module?