Hi,
Hi,
I wonder if anyone can point me in the right direction.
I'm a hobbyist building a timing system for use in amateur bicycle races in the UK. Commercially available systems use RFID tags and cost many thousands of pounds. We don't need something that gives world-record levels of accuracy so I decided to design a cheaper system.
The way it works is this: each competitor carries a small circuit with a microcontroller and passive receiver. On each lap, they pass over an induction loop. This triggers the microcontroller, that has a crystal controlled oscillator. It saves the lap time, and at the end of the race they are all uploaded to a computer. It's a lot simpler than an RFID system that would need to read multiple tags simultaneously. And at the end of the race everyone has to return their expensive tags or else they don't get their times.
I've managed to get prototypes working at both 8khz and 125khz (RFID frequency).
My understanding is that frequencies below 9khz are unregulated in the UK, though presumably there may be other restrictions on emitting magnetic / electromagnetic radiation below these frequencies (EMC considerations?)
I would prefer to use 125khz as this would be less likely to interfere with hearing aids, pacemakers or heart-rate monitors. The power I need is far less than the power that an active RFID tag requires. So I feel my system would be unlikely to interfere with anything that a legal RFID transmitter would not interfere with. But I can't find anything that confirms this frequency is unregulated and believe me I've looked hard. My tags aren't technically RFID tags as they only receive, and don't transmit.
So which frequencies might be legal for me to use? And are there any other restrictions on power output?
Thanks.