CT1 and CT2 are necessary to tune the output tank, and were 62pF and 47pF respectively on the units I built. I don't have a Mouser part number since I used what I had on hand.

The connection between R3 and C4 is present on the PT_R2 6_2_13 board. It is missing on the PT_R3 6_11_13 board, which I have never tried (and is labeled as untested in the transponder spec post). If you want to use the PT_R3 6_11_13, you should add the trace, and check the rest of the layout before making it.

are the parts the same for rev 2 and rev3 transponders?
I only have PCB layout for it. dont have part BOM and schematic. I had the rev3 pcb made and only finding those things now. but I think we will change for rev2 version, as it is tested and known to be working

Pullup resistor R7 was added on PT_R3 6_11_13. It currently has no function, and may be omitted.

C5 was added as a surface-mount part on PT_R3 6_11_13. It may be safely omitted, or used for D1 as mentioned in a previous post.

If you have already made PT_R3 6_11_13, then you should use it. One jumper between adjacent pads is a very simple correction to make. This board has been successfully used by another reader, although he did not mention the missing trace on C4. (It is very likely that the circuit functioned properly without it.)

Yes, we are currently using PT_R3 6_11_13 version. our first attempt almost worked, even with CT1 & CT2 missing (since there was no part numbers on the Part BOM, it was assumed they were not required. Therefore, the connection was not made with the antenna loop). As soon as I find those parts, we will retest. but so far, everything seems to be working.

Ok so, we did more testing yesterday on the transponder, and something weird happenned.

Here is what we did. We are using Rev3 transponder design with pre-programmed microchip from Howard. We have installed CT1 (47pF) that was missing, and added a jumper between C4 & R3 on the board to fix missing connection.

We are aware that the loop wasn't completed at the antenna, because CT2 (62pF) was still missing, but we gave it a try under the loop decoder, to see if it would pick up, and it did! but...the transpoder code was constantly changing.

We have seen:
FFFF7F
FFFFBF
FFFFFE (which is supposed to be constant)
FFFFDF

Anyone could explain?

First, get CT2 in there!

I have had the decoder occasionally miss or include bits in the ID on every transponder type I have tried, which is expected as there is no CRC used. (The problem is exacerbated when the transponder passes very slowly under the loop, so I'd guess that adding AGC to the loop amplifier might improve the situation.) However, the correct ID is always detected on the same loop crossing as the incorrect ID, so this won't affect the race result as long as the correct driver is assigned to the correct ID in the lap counting software.

I know we need CT2, we were just not able to wait to try it out hahaha ;)
So, it all looks like it will work as it is supposed to, even without CT2.

We can say that Rev3 of the board will work as well.

Not sure if this is of use to anyone, but I'm posting to find out...

Attached is 4 oscilloscope runs from 3 of my transponders, 2 rc4 one hybrid. the fourth run is two transponders on at the same time.

The files are in .csv format, you can graph them etc

I did these to see if I could end up with my transponder numbers from each capture based on all the information that has been shared on these forums so far.

hopefully the captures are long enough.

I own an rc4 decoder box as well, so I should be able to test some of these other transponders for compatibility.

I'm also interested in building something simpler than a fully fledged decoder.. Just something that decodes the transponder number and passes it along over usb. I was toying with the idea of having a plastic car stand or something, put your car down on it and my free software will show you your laps etc

I'm not sure what you mean by this... Do you want a way to just know what car you have put on the car stand in the pit?

The hard part of the decoder is the radio receiver and decoding part what i understand i have not looked much at it only tried to make transponders. But for anyone that want to play around with radio stuff using a realtech tv-tuner and rtlsdr hack it you can use it to receive 5mhz using software mod to go under the 27mhz it uses normaly in sdr mode, i have 5 of these and they work greate to listen to ham radio and other stuff around 5mhz ( with good antennas the one included is crap). But i have no idea if its posible to decode the transponder data from the radio source it can record. They cost $10 on ebay search r820t.

Unless I'm missing something, I think the only thing you wouldn't need is the timestamp, which is nearly free (it would save the cost of a crystal).

There is also the possibility of eliminating the preamble detector. That means the microprocessor would need to perform this function. But it would probably have the time to do it, since it's not trying to detect loop crossings and keep track of other cars.

It needs to demodulate BPSK. Can it do that?

I'm not sure, i have tried to figure it out if it can. Using linux radio software it have tons of diffrent phase shift functions but i'm not sure if its the same. I know to little about it still. But if it is a option i think it might be usefull for decoder functions.

yeah, pretty much. I was thinking almost like a software kiosk at the track. Put your car on the stand/whatever. It will bring the laps/sessions/etc for that transponder on a touch screen computer (like a VAIO tap21 or cheaper alternative).

(Also interested in a rc4 compatible decoder as well, but that's a different forum. We're setting up sector times at the track at the moment. One RC4 decoder per loop is a bit harsh on the wallet.)

Ordered something from amazon, I'll give it a try. thanks!

Cool idea.

But regarding the radio receiver, As I said I'm not even sure its possible yet. But they are cheap and fun to play with if you like radio so it might not hurt to buy one anyway.