I thought some of you guys might appreciate this new comm system I built for my 24 Hours of Lemons track car (endurance racing).
UPDATED March 2017 - Ver 2 now
* Since our first race back in 2010, we've relied on a DIY system involving some proprietary digital spread spectrum FRS radios (it's digital so you don't step on anyone else's chatter even with 170 other teams on track), a DIY antenna, and some DIY headsets.
* Even using a "motorsports" connector (one plug with microphone+speaker), the wiring inside is very, very thin and I'm sick of repairing headsets when people forget to disconnect when jumping in/out of the car.
* The headsets never really worked anyway after we started renting a pit garage space at Sears Point -- they are essentially giant faraday cages. Even with a 30' antenna sticking out of the garage window track-side, the grandstands block your line of sight to most of the track.
* I don't want anyone chattering in my ear while trying to keep my tbird away from the 169 other idiots on the track. We are fast enough now with a V8 that we are trying to weave through the traffic (vs just trying to thread our way fron the front of a pack if faster cars to the back of the pck).
* The driver really only needs to tell the pits one thing "hey, I'm coming in."
* The pits SHOULD have the ability to signal the driver to come back in though.
* Cell phones work inside the Sears Point garages.
* Arduino compatible cell phone modules are really cheap (esp 2G ones). AT&T will be turning off 2G service by EOY 2016 but TMOBILE doesn't show any signs of turning away all the cheapie IOT biz.
(1) Sainsmart ARDUINO Nano ($11.99)
(1) NRG Steering wheel with buttons on it (already had it. Because 2 fast 2 Furious).
(1) Sainsmart Small GSM SIM900 comm module ($27.99)
(1) LION Battery: needs to output 2A for the comm module
(1) SIM with a few bucks loaded in. NOTE: the really sketchy cheap guys, FreedomPOP, use an android app for SMS texts so it won't work with my module. (TING is a Tmobile MVNO who offers SIMs for $1 on sale. 1 month of service with 1K SMS cost a mere $11)
(MISC) Small proto board, connectors, scrap box, USB cables, etc - <$5.
(1) 12V to USB 3A DC-DC adapters hardwired into car. You need two because the Cell modem takes too much power from the converter for the arduino to boot correctly
WHAT THE SYSTEM DOES - VER 3
* SMS texts the pit crew upon boot up "Ready to Rock". Current code sends messages to ALL drivers.
* Steering wheel buttton replaced with a two switch panel mounted where the sun visor used to be. Even with a helmet + hans, a driver can quickly operate the system without looking up and he won't accidentally trigger it.
- Right switch = New Driver/More fuel
- Left switch = Repairs needed
- BOTH Switches = OMG! Some shit went wrong. Get ready for big repairs.
* Pitcrew only texts car when THEY want the car to return to the pits (no acknowledgement). If the correct callerID and phrase is matched (screw you, rival team haxxors), a giant red LED light is illuminated in front of the driver.
* Driver/reference code availability. I eventually found a reference to a usable GSM library and sample code in someone's product review on amazon. Thanks, more-determined-nerd-than-me.
* It took me a bit to realize that the comm module will work with only 100mA of current to stay on network but needs up to 2A to transmit. If you give it too little current, it starts acting squirrelly.
* When sending multiple SMS messages, you need to wait a decent amount of time (10 sec delay) between sending messages or the modem (which works asynchronously from the Arduino) will mess up. The alternative is to redo the GSM library to actually read back the AT commands the cell modem returns vs the "fire and forget" mentality it uses today.
LESSONS LEARNED AFTER FIRST RACE DEPLOYMENT
After my 7th Lemons race, I learned two key lessons:
1) Do NOT put the button on the F&F style race wheel because someone will tap it accidentally. Move it. Even better, don't make it a button -- make it a switch.
2) The communication protocol should be that the Pit crew only turns the "RETURN TO PIT" light on for the driver when THEY want the driver to pit and not as an acknowledgement of msg received. if the driver wants to pit, hes going to do it anyway. We had two inadvertant pit stops when the driver accidentally pushed the button, the pitcrew acknowledged the message, and the driver saw the light and thought that the pitcrew wanted him to come in. Whoops.
3) You need more info from the driver to the pit to decide what to do. For example, for fuel or driver change stops, you need someone on the pitcrew suited up in a driving suit. For repair stops, you need the "mechanics" of the team (we have two mechanics and one chef) suited in their repair coveralls and ready to work.
1) Works Great