Hi All

I have got the files from Howard (many thanks) and wondered if anyone out there has spare PC boards I could purchase for the decoder please

I'm glad you have found the thread to be informative.

I have never seen an FPV race, but I'll bet it's a bunch of fun!

I think the detection range of the system will be too short for any flying vehicle. If the largest loop is used, the active area would be perhaps 2x12 feet. One could also fly the FPVs through the inside of the loop, but then the loop would need to be no larger than about 5 feet square, and there would be a good possibility for colliding with it. In either case, orientation of the transponders to the loop would be highly variable, giving erratic operation.

I was thinking about flying through the inside of the loop, but 5 feet square is really narrow. Collisions are really common in this kind of races, as the circuit is usually composed of a series of gates or arcs to pass through them, but wider.
One thing that could be really useful will be that if you pass inside the loop you'll get detected, but if you pass outside you won't. Sometimes it's a bit difficult for the race judges to check this conditions to ensure that everybody is racing inside the circuit.
If a transponder pases close to the loop but it doesn't pass through it will be detected?
About the transponders orientation, it will be very variable indeed, so maybe this design won't work at all.
If I want to use a wider loop, do I have to use a lower carrier frequency? will it need a complete redesign of the analog circuit? I am not particulary interested on compatibility with other systems, so it doesn't matter if transponders or decoders from other brand don't work.

Transponders will still be detected if they pass close to, but not through, the loop.

The maximum size of the loop in the design presented here is restricted because it is used as part of a resonant circuit to filter noise out of the signal. There are other ways to get larger detection areas without going to lower carrier frequencies, but as you have surmised this requires a different (and more complicated) analog circuit. Using a lower carrier frequency has the disadvantage of less efficient radiation of the signal for a given size of transponder, and I'd guess that larger transponders are not good for your application.

An optical system seems well suited to your application. Its advantages include very small and lightweight transponders, and good isolation between different detection gates (if that is a good term to use) on the race course. But each detection gate would be much more complicated than a simple loop of wire.

If I were to design such a system, I would put two (or more) LEDs on each transponder, sending the same signal but in opposite (or orthogonal) directions, and each detection gate would be a square or rectangular frame with photo detectors mounted on the frame, all facing inward. To prevent false detection of a transponder outside the frame, the decoder would require that the transponder signal be detected by at least two sides of the detection gate. This is not as simple as it seems, because the signal would not necessarily appear at the same instant in different sides of the gate due to the random angle of the transponder.

Thank you for all the clarifications.
Looks like this system is not the suitable one for fpv racing, but if I ever need a lap system for rc cars this is the way to go for sure.

My first thought about the detection gates design was to use infrared leds and phototransistors. I have used them before for slot racing with good results and with very simple and cheap circuits.
The infrared transponder will be a really simple and small device, but the gate gets complicated as one must use an array of sensors. The i-Lap system requires the sensors to be placed every 50cm I think.
Since I would like to have all the gates that define the track "active detectors", each gate should be as cheap as possible. I will keep looking for different implementations, maybe I will be lucky enough to get an affordable one.

Hi All

I was looking at the cost of getting decoder and amp PCB's made up and the cost for multiples is not much more than for one. If there are any folks out there who want a set of PCB's to build their own decoder please post on the thread if you wish to be included in a group purchase so we can share the cost.

You're in London? So am I, and I would be interested in a PCB (or maybe even two, depending on the cost).

Cool, you are on the list maybe we can join forces on the build as well.

Where do you race?

I have 4 boards available, $35 ea. + shipping. I have my decoder just soldered up today, need to get a trimmer pot, and project boxes then I am ready to test.

I'm interested in PCBs as well! One or two depending on cost, and shipping to Sweden. Also transponder pcbs by Howard is of interest.

Nice one, love to hear how testing goes.

Do you have amp boards as well as the decoder PCB's?

I have done a bit of searching around on pricing and OSH Park in the USA have pretty good pricing for low volume as follows:

Their minimum is 3 pieces and more items only in multiples of three as far as I can make out.

$122.20 for 3 x Decoder PCB
$5.70 for 3 x Amp board

So a pair (decoder and amp) of PCB's comes out at around $43 which is £28 or 354 SEK plus shipping.

I work in the US a lot so can avoid UK customs duty and charge if I get them delivered to the US and I will bring them in by hand.

I will also be getting Transponder PCB's, they are $2.61 ea ($7.85 for 3) if you are interested.

Here is my H.w.Cano loop amp board pic. I cut this on my engraving machine.
It is a little harder to solder components without a solder mask, you have to have a steady hand.

Very nice job, shame it can't do 4 layer boards ;-)

Yes, interested! A pair of decoder + amp and 3 pcs of transponder PCB's would be great. I'll PM you for details.