Its 3am so forgive me if this isn’t clear - I wanted to write it down before I forgot.
I was looking at cheap RFID reader boards, and saw a lot of people commenting that the cheap Chinese ones aren’t tuned well from the factory. The good ones use a variable capacitor that is tuned in the factory for best performance.
I was wondering if there was a way for a reader to constantly tune itself to give the best performance, given that capacitors loose capacitance overtime. Also if there was a way to do it cheaply.
My idea:
Get one of @Hamspiced’s LED field detection PCBs, put it in a housing with a photosensor, add an arduino, and bam, cheap realitive signal strength meter. This will allow you to measure how bright the detector is, which can give a relative idea of the performance of the reader.
You could even add in another LED powered by the arduino, with some current sensing you can map the analog values from the photosensor to current - allowing rough calculations of the energy an RFID tag is able to get at some position.
Benefits:
Easy quantifiable RFID signal strength measurements for dirt cheap
I had an idea to have multiple LEDs in line with some small resistors to see if the wireless energy was strong enough to power multiple LEDs even dimly so you could get an idea of field strength. Then I thought it would be easier to add in a small analogue sweep. But I didn’t think the juice was worth the squeeze to go forward with the project. I wanted to get an LF repeater out first.
There are better ways to do this that don’t involve an improvised opto-coupler. Also, you don’t necessarily need a fusking arduino for everything! Designing analog circuits appears to be a lost art nowadays…
I’m getting old, send help.
I think that adding a battery would be ok for something like this.
Jammy is proposing using a field detector with a sensor right next to the led that measures how bright the led is. Then wire it to a microcontroller to give data back in decimals how bright it is.
I am saying have one or multiple LEDs connected to resistors so it will only turn on at specific voltages.
Jammy has a solid plan but the data will only be as good as the minimal voltage required to drive the led. Same with my idea but I would possibly add a small battery to make up for it and help drive the lower current fields.
If you check the link I sent something like what I proposed is already available. So I thought maybe use a analog sweep gauge. May be more sensitive.
This is basically how the NXP demo cards work for the ntag 5 fam… though they are using it to show power harvesting output voltage settings… but could work for field strength… and it’s cheap to produce.
I’m not really full bottle on the RF side of things so maybe it’s more complex than I am imagining, but couldn’t you just put a resistor across the coil and measure the voltage across it?
I’ve just hooked one of Hamspiced’s coils (no capacitor) across my multimeter in mA mode (essentially using the meter’s internal shunt as the resistor) and it gives readings that vary as I move a PN532 closer and further away.
I’m not sure if a typical Arduino’s internal ADC would be precise enough, and you might need some 0.1% resistors to get a good reading, but it seems like it should work and it gets rid of all of the stress about voltage drop of LEDs.
I didn’t want to take an approach like that because I don’t know enough about RF/electronics to understand how measuring the current like that would affect the antenna circuit. I have a super basic understanding of electronics but all this RF stuff is black magic
I have made a variety of different antenna’s which are used in my projects and their inductance is known. if you wanted to take on a project like this i would be happy to send you what i have as well as provide the gerbers for the antenna.
