MidwestGadgets.com - Repeaters, Field Detectors, Generators, Extenders Oh Myyyy! New Product and Stock Announcements Thread

[Pilgrimsmaster]

Dude, your arsenal of RFID related products are awesome.

That meter of yours is perfect for confirming what the minds eye has been “seeing” when testing readers and your repeaters; but the fact it puts a number on it is a significant step better.

I feel like if we collect some sample mV figures for implants to be read, we can likely predict if a reader will work and or if a repeater will help a stubborn reader enough.

I don’t want to suggest a spreadsheet, But…
even a note/ column in the compatiability matrix.

Pretty exciting

Loving your work as usual

[Pilgrimsmaster]

The standoff I have thought about in a few scenarios, often just using the housing is a good option (depending on where the antenna is) but being able to actually see with your meter, means optimising the chance and range of reading.

I’ve though a modified Pizza Tripod with a repeater on it would be a good option in some scenarios, cut/ bend/ melt the legs to suit

[Hamspiced]

@Pilgrimsmaster

Dude, your arsenal of RFID related products are awesome.

Thankyou!

@Pilgrimsmaster

I feel like if we collect some sample mV figures for implants to be read, we can likely predict if a reader will work and or if a repeater will help a stubborn reader enough.

So i am going back and forth on whether to use MV or Voltage. Currently the numbers are incorrect. I am displaying millivolts on the display but its using a voltage divider to get this number and it isnt correct other than being very granular on when the field is detected.

In reality the ACR122 is puting out around <5v but this is the thing i need to determine.

Do i build it with arbitrary values that just give a readout depending on its proximity to the field.

Do i build it with actual voltage values and try to tune these to be relatively accurate?

[Pilgrimsmaster]

@Hamspiced

So i am going back and forth on whether to use MV or Voltage.

Personally I dont really think it matters, it could be 9.3 MegaHammys, but you still know that is better/ more that 2.7 MH…

The ACR is measured at 5MH…close to, but maybe not exactly 5V

@Hamspiced

Do i build it with arbitrary values that just give a readout depending on its proximity to the field

Ah, yes, I should have read your whole post before replying.

I think if its to difficult (time consuming) to be accurate with a known scale, just make your own

[Not]

@Pilgrimsmaster

I feel like if we collect some sample mV figures for implants to be read, we can likely predict if a reader will work and or if a repeater will help a stubborn reader enough.

This is exactly what I was trying to suggest above, but better worded and more well informed.

@Not

it probably wouldn’t be too hard to make a loose chart for required minimum voltage for different implants.

[Hamspiced]

Not trying to tune it to a real world value makes it quicker and easier to put together and then tune so that all units are relatively the same. So as long as this meter is used all the values will be the same.

If i tune it to an actual standard we will know the specifics but the tradeoffs will be:

1. Wont be able to see where the effective field begins
2. Additional components or an opamp or voltage dividers to do some voltage summing depending on the standard that is decided upon.

Also i want to also make this as an Analogue meter as well since these digital displays cannot pick up the pulses generated by phones. the pulse doesnt stay active long enough.

I will say though that Iphone’s output about 1/3rd the power of the Google Pixels. Which also explains a lot of why people with apple devices have issues. So that has been confirmed

[Not]

@Hamspiced

I will say though that Iphone’s output about 1/3rd the power of the Google Pixels. Which also explains a lot of why people with apple devices have issues. So that has been confirmed

As someone running a Pixel8 and Pixel4a with a gf who runs an iPhone16, this tracks.

[Pilgrimsmaster]

@Not

This is exactly what I was trying to suggest above, but better worded and more well informed

Oops, My bad, yours is perfectly worded and YOUR idea must have been in my subconscious.
I totally agree with YOUR brilliant idea @Not

[Hamspiced]

In part of testing things with my meter. Does someone have an underperforming NFC lock I can purchase from them that:

1. Should work but does not.
2. Does work but only with a repeater added
3. They have no use for.

Would love to get some base readings with this. I’ll pay for the device and shipping

[tac0s]

@amal dead pool lock?

[amal]

Absolutely Deadpool lock. Would be cool to see the difference with and without rsp

[Hamspiced]

I’ll make sure Wade is returned to you.

[amal]

@tac0s don’t we have two of those? Even if not, @Hamspiced feel free to keep 'ol deady… I’ll never be using it… like ever. Actually I think it’s cursed. Have fun with him!

[tac0s]

Just the one. I’ll have to dig it up.

[Jammyjellyfish]

Relatively accurate means that all data gathered by this version, future versions, and any other meters that pop-up, will all be self-consistent. Strong vote for trying to make it accurate to known values

[Jammyjellyfish]

@Hamspiced

Wont be able to see where the effective field begins

why is this the case?

[Hamspiced]

Going with volts in limited to a 3 digit readout. 0.01 volt won’t encompass where the field begins.

Going with millivolts will show more granular strength but will require a voltage dividing circuit. Issue we will run into is tolerances not necessarily being accurate enough for it to be accurate within a reasonable margin of error.

+/-1% tolerance on a cap is still enough to produce wildly different readings at this scale.

And lastly it’s I don’t have a frame of reference. I’ll need to invest in some equipment I can reference as a standard to tune the devices to.

[amal]

@Jammyjellyfish

Strong vote for trying to make it accurate to known values

My question is - what are you trying to do? What is the goal?

If the goal is to be able to find the physical location of the strongest signal over a particular reader, megaHammies is a fine unit of measure.

Having a goal that would require readings calibrated to some sort of “absolute truth” like voltage can easily push a fun cheap little hobby device into lab bench equipment territory in terms of complexity and cost. Hell even a few degrees difference in temperature will change values as capacitors change capacitance and induction coils change size due to thermal expansion. Calibrating these would then require thermal sensors, EMF design considerations, etc. etc. etc. not to mention maintaining calibration accuracy over time becomes a thing… how accurate must it be and for how long? Ultimately, is achieving the goal worth the effort?

Personally, I think current is a good idea, but it doesn’t have to be super accurate or calibrated… a low accuracy device that does work with inducted current measurements. The reason is that voltage per meter is a common RF electric field strength measurement metric, but for magnetically coupled devices current is generally measured.

chatGPT word salad…

For a magnetically coupled device, the equivalent measurement to volts per meter (V/m) in the electric field domain would be amperes per meter (A/m) or magnetic flux density in teslas (T).

Key Magnetic Field Strength Measurements:

1. Magnetic Field Strength (H-field): Measured in amperes per meter (A/m), this represents the strength of the magnetic field generated by a current-carrying conductor or coil. It is particularly useful for near-field magnetic coupling applications like NFC or inductive power transfer.
2. Magnetic Flux Density (B-field): Measured in teslas (T) or microteslas (µT), this represents the amount of magnetic flux per unit area. In free space, B and H are related by:B=μHB = \mu HB=μHwhere μ\muμ is the permeability of the medium.
3. Magnetic Potential (Φ): Measured in webers (Wb), it represents the total magnetic flux and is often useful for evaluating inductive systems.

For magnetically coupled devices (such as NFC, RFID, or inductive charging), the H-field in A/m is typically the most relevant metric, as it represents the intensity of the magnetic field responsible for coupling energy between coils.

In applications like NFC (near-field communication) and RFID, standards like ISO 14443 and ISO 15693 define operating fields in terms of H-field strength, where for example, ISO 14443 specifies a field strength of 1.5 A/m to 7.5 A/m at 13.56 MHz.

Dug up some relevant docs…

ISO-IEC-14443-2-2020.pdf (541.6 KB)

ISO-IEC_15693-1.pdf (80.2 KB)

[Hamspiced]

Originally I had this setup with a hall effect sensor and an opamp driving a display but I had literally no idea what the hell I was measuring. So I want to say least settle on a unit of measure. I would prefer volts only because analogue voltage gauges are easy to come by in small increments and I can easily adapt the circuit to it.

Talking through this. If I do go the voltage route I could increase the signal and just say whatever the reading is just subtract 1v and this is your true reading. But for display purposes we wanted to capture the data

[Jammyjellyfish]

Could use some dedicated IC like this, read it using a attiny and display on a cheapo oled display