I've got a gizmo that uses a pair of coils to detect the presence of an "authorization" device that ensures it is only used with "genuine" products (think: toilet paper dispenser; you want to make sure only YOUR toilet paper can be used in it! Or, toner cartridges or...)
The coils are about 3/8" diameter, stacked one atop the other (small gap). Three conductors so think of the coils as one, larger "center-tapped".
The portion of the "replacement cartridge" that fits inside this coil effectively limits the volume of the "magic bean" to roughly that of a 1W carbon-comp resistor (i.e., there's a fair bit of plastic packaging involved that eats up much of the volume).
I don't have an example of a genuine product (cartridge) to examine. And, the circuitry is completely integrated -- just three wires from the coils heading off to an ASIC -- so no way to see what's going on in the "accepted" case (nor any way to jumper around the "authenticator mechanism").
I suspect the design must recognize "no cartridge present" as well as "wrong cartridge present" -- which implies there are multiple "identities" that the gizmo has to be able to detect/differentiate.
Before pulling out a DSO, I figure the things that the circuit could likely look for would be the amplitude of a "sensed" AC signal fed back from one coil (while the ASIC drives the other coil). This would work if a small diameter pair of coils was inserted between these (i.e., provide a particular gain in the windings ratios)
I'm sure other aspects could be used (alter the phase of the sensed signal, etc.). But, the space limitation (AND the cost -- note that you are making a disposable item!) is an issue.
Ideas as to what they may be doing? Or, suggestions as to most fruitful way to proceed?
The coils are about 3/8" diameter, stacked one atop the other (small gap). Three conductors so think of the coils as one, larger "center-tapped".
The portion of the "replacement cartridge" that fits inside this coil effectively limits the volume of the "magic bean" to roughly that of a 1W carbon-comp resistor (i.e., there's a fair bit of plastic packaging involved that eats up much of the volume).
I don't have an example of a genuine product (cartridge) to examine. And, the circuitry is completely integrated -- just three wires from the coils heading off to an ASIC -- so no way to see what's going on in the "accepted" case (nor any way to jumper around the "authenticator mechanism").
I suspect the design must recognize "no cartridge present" as well as "wrong cartridge present" -- which implies there are multiple "identities" that the gizmo has to be able to detect/differentiate.
Before pulling out a DSO, I figure the things that the circuit could likely look for would be the amplitude of a "sensed" AC signal fed back from one coil (while the ASIC drives the other coil). This would work if a small diameter pair of coils was inserted between these (i.e., provide a particular gain in the windings ratios)
I'm sure other aspects could be used (alter the phase of the sensed signal, etc.). But, the space limitation (AND the cost -- note that you are making a disposable item!) is an issue.
Ideas as to what they may be doing? Or, suggestions as to most fruitful way to proceed?
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