Thanks.. I actually dislike through hole and especially stripboard, so I took some time over it. I'll hope to move it to SMD once it works.

I have not yet studied the decoder schematics in detail, I hope to start this week during vacation. How is it that the digital phase detector knows when the phase has reversed? You say that there "may" be a missing pulse, but in a perfect situation how does it recognise the modulation?

I am going to play with tank tuning values tonight to sort out the Q as you suggested, this should help.

Here is a quick description of the phase detector operation:

http://www.rctech.net/forum/12009638-post167.html

Hi Howardcano,

Can you explain how the RC4 decoder can filter out the PTX transponders? Afaik the PTX is a clone of the AMB PT so how can the decoder see if it is a PTX or AMB PT?

Great Thread. I was actually trying to analyze many years ago how the decoder system worked but never got a break through.

Thanks.

There are many possible ways to distinguish the old MRT from the old AMB, and I mentioned a few on my Transponder Design thread. But I don't know what method is used.

MRT has figured it out, though, and has released an updated transponder that is again indistinguishable from an old AMB transponder by the RC4 decoder.

So now it's up to MyLaps to 1) do nothing, 2) figure out other differences to look for and use as a basis to reject MRT transponders, or 3) simply don't count any MRT and AMB transponders anymore. Don't be surprised if it's #3.

Well attached is a picture of my high quality, made at the very last minute decoder! The green board is a Lattice CPLD and the stripboard contains an oscillator and Howard's phase detector input amplifier. The barely visible purple board (to the left) is a PIC breakout board. The whole thing is powered from USB.

The other picture is the loop amplifier which is slightly neater construction and is made to fit into a small enclosure.

I'm going to give it all a trial next week at a karting camp - will report back. Nothing like taking a development model to a real event

Thanks again Howard.

That loop amplifier is a work of art!

Good luck with the karts. It will be interesting to hear how well the system functions with the buried loop and all the ignition noise from the kart engines.

Day one of our camp and I've got mixed results. Works great under a carpet with some RC cars, but not with the loop which is buried in the go kart track.

The loop in tarmac for the kart track is rather long and too far apart (a few feet) - the cable is probably 2mm twisted copper. We are hoping to try a much thinner wire in the next few days.

Can you get the buried loop to resonate at 5 MHz? If it's too big, it won't tune high enough, and won't be effective.

Some news about my arduino / EPLD howardcano design decoder.
The EPLD and arduino interface are done, now it's time to develop the smart phone & PC software.
Hardware :
one arduino leonardo board
one ethernet shield
one PhaseDetectorInputAmplifier & ALTERA EPLD on prototype board
one Howard LoopAmplifier



Thanks again Howard.

Very nice! It looks like you are making good progress!

Why do you use the LM319 component in 3V3 power supply instead of 5V ?
The LM319 is designed to operate with a power supply > 5V

thanks

I just finished revision B of the decoder software. The LED now blinks off momentarily after a transponder has passed under the loop. This will help during troubleshooting to make sure the loop is active. The copyright notice that is sent via RS232 on power-up contains the revision identifier.

The copyright notice can be used to check for proper operation of the serial port on the PC (using a terminal program such as PuTTY).

howardcano, Hi, can you explain the role of Q5 transistor in your amplifier's schematics?
And 2nd question - what is the maximum distance of transponder detection from the loop? Thanks.

Q5 provides a temperature-compensated bias voltage to the bases of Q1 and Q2.

The detection distance will vary depending on the location of the transponder in the car. The transponder needs to be well away from conductive materials like aluminum and carbon fiber. The maximum distance is about 2 feet.

I have updated the decoder schematic and BOM. The changes are to support FlipSide software. This software sends a message on the RS232 line into the decoder to reset the internal timestamp counter at the start of a race.

Post #251 shows the latest revision names:
http://www.rctech.net/forum/12222187-post251.html

The changes include:

R66, a 10K resistor, is replaced by D60, a 1N4148 diode.

The 221R resistor at R69 has been moved to location R68. R69 is now omitted.