View Full Version : great C/S and Q re: IR lapcounter technology

2007.10.31, 09:36 PM
Hi Craig,

I wanted to say "thanks" to a quick response to my questions about the I-Lap system. I also wanted to let other mini-z enthusiasts know my experience by posting something in the forum about the great customer service you've shown thus far.

I do have an additional question which is posed generally on IR technology based lap counters...this question could be asked to other IR lapcounters, but thought I'd ask you.

A techie friend of mine asked me the following for which I couldn't answer; hopefully you can and allow others to see the answer.

- if two identical cars in all respects (chassis, height, body choice etc...) are neck and neck down the straight and about to finish the race, both have their transponders attached in the exact same spot (same part of chassis), but car 1 has their transponder slightly angled forwards (towards the front of the car)(note: this could have happened on purpose, by accident etc..., no matter how though) and car 2 has their transponder facing exactly straight up. If both cars cross the start/finish line (i.e. bridge) at exactly the same time, will an IR system count car 1 as finishing first? My friend thought yes as light can be directed...so theoretically someone whose transponder is pointed forwards will reach/be picked up by the sensors 1st. This may not be the case, but wanted to ask.

Thanks in advance.

2007.10.31, 11:56 PM
I don't work for an IR lap counting company but I am an electrical engineer who works with other infrared systems and I have a good idea of how these systems work.

The answer to your question is likely yes. The car/transmitter which first achieves a line of sight with the overhead bridge receiver will be counted first. So, pointing the car's transmitter slightly forward will advance the line of sight. The timing difference may however be rather insignificant.

This little bit of information may help you draw a picture of the line of sight:
- Infrared LEDs can be manufactured with very narrow patterns (2 degrees or less) so think of the transmitter beam as a line of light about 3mm round.
- The infrared receivers (phototransistor or photodiode) used will have much wider patterns in order to cover the width of the track - use the recommended bridge height and receiver spacing to figure it out.

To eliminate any concern about this all you would have to do is place a cover of sorts on the incoming side of the bridge forcing the transmitter to be closer/nearly under the bridge before its counted.

I hope this helps a bit. I too would like to hear the "official" response from the engineers of these systems.

2007.11.01, 11:10 AM
Theoretically, it is true. Recessing the sensors in a channel or some sort of barrier on the front side of the bridge would eliminate this. It largely doesn't matter because the car with the transponder tilted forward would have theoretically started the lap the equivalent distance sooner, so any advantage gained at the end of the lap was already removed when the lap started.

2017.05.21, 01:13 PM
How do you best handle infrared LEDs with wide angle patterns? There are 3rd party transponders that are compatible with I-Lap receivers however they LED pattern angle is MUCH wider allowing the receivers to pickup the transponders from much father away. so much so that one would need to place a visual barrier between the timing bridge and adjacent lanes. this is regardless of the angle it is mounted at in the car.
i've been looking into TEMPEST style glass films that block RF/IR signals as a possible solution to build an acrylic panel with this film as a measure to prevent unintended signal reception from adjacent lanes however i do not yet have a physical mock up to test performance. i've tried increasing the depth of the bridge channel in which the sensors are placed with no effective results. I suppose i could also test the channel depth with variation in height as well but that doesn't seem to solve the issue of unintended pickup in an adjacent lane.

anyone else run into this problem?