If it's a slew rate problem in the driver, then yes. It could also mean that the driver is clipping.

No matter, it passed. I've had my own designs pass by a lower margin, but we usually tested at least one more sample when that happened to give some indication that tolerance wouldn't push production units over the limit.

Here’s the status of my transponder design:

I now have all of the circuit boards populated, and tested them last night. Most of them have the same program, containing a single ID number that I will use on all of my cars (there are so many of them!). So, one of my goals for the project has been met: create cheap transponders that I can leave in each car, eliminating the hassle of moving a transponder from car to car. (The same ID number will also make things a bit easier for the person running the scoring PC when I’m running multiple classes, as my information will only need to be entered once.) I’ll also retain the AMB transponder that has this ID number.

I also made a couple of boards with different ID numbers for use in my “loaner” cars that I let other drivers race in our Breakout class at the local track.

The second goal, having a design that might be commercially viable, is nearly complete. To this end, I tested the new program for the PIC12F683 that contains multiple ID numbers. There are currently 25 numbers that I code-compressed, and most of them operated correctly. The ones that did not function had obvious errors (in hindsight!), and they are now fixed and ready to re-test. (Hopefully there will be time to do that this Sunday.)

The ID selection is pretty simple: power-down, place a jumper on the 2-pin connector (or short the pins with a metal object), and power-up to step to the next selection. If the jumper is left on the 2-pin connector, then the microprocessor loads a new number each time power is applied, which makes my testing pretty easy—turn the car on, run it twice over the timing loop, record the result given by the scoring PC, then turn the car off and on again to test the next number.

There is, however, no indication of which ID number is selected on the transponder, so it might be a good idea to add some code to blink the LED in an appropriate pattern whenever a new ID number is selected. One to four blinks to indicate the ID set, and one to eight blinks to indicate the selection within the set, would work quite nicely for the 32 ID numbers that will fit into the 12F683. It will also be easy to increase from four to eight sets (as there is a PIC12F microprocessor currently available with a larger memory that would hold perhaps 64 ID numbers).

I’ve got several more transponders on the way, and will fill up the remaining ID number memory as time permits, but other than that I think I’ve reached a reasonable stopping point.

It’s time to try the loop amplifier design for the decoder!

I think the question on everyone's mind is... when can I buy one

And can you clone my amb? I also like to have the same number in each car.

I have no immediate plans to spend the thousands of dollars required for FCC testing on complete units. However, if you want to experiment and are well-versed in electronics, please read post #67:

http://www.rctech.net/forum/11708230-post67.html

I may pursue selling the design to an individual or company that wants to produce these, but I have no news on that right now.

Yes, I can "clone" numbers. That's the only way I can create programs at the moment, since I have no idea of the data format used by AMB.

Great job. Waiting for news. I am very intersted in your work

Here are some photos of the tranponders in a few of my cars. They illustrate the size of the transponder, 1.25" square, in its current, through-hole form. The first shows an HPI 235mm-wide HPI 1/10 scale pan car that I use in our local Breakout class. Plenty of room here:



Here's a 200mm-wide SpeedMerchant WGT car, still with plenty of space:



I had to mount the transponder on top of the steering servo on my XRay T1 VTA car (the smaller AMB transponder was on the chassis directly on front of the receiver):



When we get to a 1/12 scale car, this Carpet Knife 3.2, things start to look ridiculous, but it does barely fit, and still makes minimum weight:

I updated the schematic using TinyCAD. If anyone wants to lay out a smaller, surface-mount PCB, I can PM a netlist to you. I would suggest using four layers, both for ease of routing and to make the tank inductor dimensionally smaller (since it can have turns on all layers). Remember, NO POWER OR GROUND PLANES ARE ALLOWED, as they would keep the inductor from radiating the necessary magnetic field!

The design now includes a Zener diode to permit operation from 5V to 6.6V (a 2-cell LiFe or 5-cell NiMH receiver pack).

U1D may be eliminated if single-gate packages are used.

Hi Howard,
i have seen several schematics where oscillator freq is sourced form osc2 output of pic.
Xtal is connected between osc1 and osc2 and you can source freq from osc2 as it is output of internal gate. With such configuration you can save U1A, U1D and R2.

Unfortunately, it doesn't work that way. The output from the OSC2 pin on the PIC is nowhere close to logic levels. Actually, I've never used a PIC over the last 20 years where the OSC2 output was at logic levels. But it would have been nice to save some parts!

It would be even nicer to use the internal RC oscillator, but the accuracy and temperature drift eliminate that option.

in hs mode it is working for sure, i was driving cmos buffer by osc2 and feeding second pic but these gates are there anyway

I think that for the SMD version an ICSP connector can be really comfortable.
Why GP4 is connected to the power connector ? Debugging purposes or additional features ?

Last question, why do you put a rubber band in the steering of your pan cars ?

Yes, that would be ideal!

Additional features, which I won't reveal at the moment. It would also be handy for debugging, although I have only used the LED for that up to now.

That removes the slop from the ball joints. It has the advantage that when I hit something and add to the slop, it is immediately taken up by the rubber band. I use rubber bands on all of my cars, not just the pan cars.

Any chance of a higher voltage limit for those of us who run 2s lipo receiver packs?

That can be done by including a voltage regulator IC. I'll keep it in mind for the next layout. If someone does a surface-mount layout, that would be a good time to include it.

EDIT: Changing R1 to 100 ohms will also do the trick, but then the minimum voltage required for operation will be about 6V.

If you have the design already debugged and tested, I would be happy to help with a surface mount layout. I already have done SMD designs of ESC for RC cars using four layer PCBs.

I am not interested in adding an LDO into the transponder design. What I am interested in would be an open source design alternative to the AMB units, with the power supplied by the existing BEC in the ESC.

Anyway, I would be happy to do the SMD PCB layout as long as this design will continue to be an open source project to benefit the RC racing hobby and community.