I noticed that my xMagic has better LF range if I stick the diagnostic card between my hand and the reader.
Strange, but I’ll take it.
I can’t figure out why though. Does anyone have any thoughts?
My first guess is that the card is drawing just enough power to somehow “wake up” the reader into a higher power mode. Either that, or there’s some unexpected antenna resonance magic happening.
This comes as I am fighting with a few readers that really don’t want to read the xMagic, yet will read a keychain fob at a few inches distance.
It makes sense it can help shape the field. We totally could create a LF repeater using the diagnostic card. I never considered it because the overall footprint is bigger than I feel is reasonable for a repeater
Well, I’d certainly be interested in a repeater of that size, just for the sake of having anything.
I imagine packaging that circular coil in a slightly flexible plastic could make for a nice form factor.
I didn’t see a viable way to make an LF repeater in flex. Not yet at least.
I don’t have access to the diagnostic card files but I could look at a quick way to convert diagnostic cards into make shift repeaters. It will sacrifice the led though…
The diagnostic card and really any field detector with an LED load will not work great as a repeater for two reasons. The first reason is that there is a load in the circuit in the form of an LED which will sap quite a bit of power from the field, and the other reason is that the LED is rectifying the signal, effectively chopping it in half.
What is much more likely is you have encountered a reader that uses field pulldown detect function to operate in a low power “probe” mode until the reader detects a significant power draw from an inductive load (a transponder). The problem is that most x-series do not have sufficient inductive coupling to effectively signal to the reader that a transponder is there and ready for communication. Adding the diagnostic card creates the required load to trigger full power operation. The actual communication being done though is basically between the reader and x-series chip, and not really helped all that much by the diagnostic card.
Sometimes readers configured with these power saving features will also change their duty cycle… but not always. You can check for this by holding the diagnostic card far away and coming closer very slowly until you barely see the green LED lighting at all… best to do this in dark conditions of course. Then bring the diagnostic card much closer and see if the duty cycle changes. You may even be able to detect a significant jump in signal strength when full power mode is triggered, but only if you were able to precisely control the distance of the diagnostic card from the reader and ensure the LED intensity gains you will see by moving it closer are moving linearly with your proximity, until a jump and intensity is detected which does not correlate to physical proximity changes. Not an easy task to do by hand. Even in a lab it would be kind of a challenge.
Many readers with this type of setting also allow sensitivity to be configured. Some readers are set to trigger on any kind of field shenanigans while others require quite a bit of inductive load detection before triggering full power. Maybe your readers are configurable? I seen configuration done with jumpers and also with special commands into non-volatile memory.
That’s pretty much what I was thinking.
The reader didn’t seem to change its duty cycle when “woken up”
I’m going to try to see how long it stays at this higher power level after I present the diagnostic card to it.
Interestingly this only happens with about 50% of the readers in the building. The rest run at a very high power level constantly.
Do you know the brand reader
I’m not entirely sure what these are. My visual-reader-identification-fu isn’t that great.
My testing says the LF antenna sits right under the logo, and spans most of the width, but not all of the height of the device.
Any chance you could check the back side for jumpers to configure low power mode?
We should have another chat about that now that I’m not running all over kingdom come. I’m sure we can figure out a solution that’s viable, it just might not be in the same form factor that we’ve been using.
