charliedontskate.com

[Bugs]

Some info here about wireless timing systems:

http://www.slalomskateboarder.com/phpBB/viewtopic.php?t=5369

The wireless transmitters/receivers have a 3 km range, and they cost about the same as the 300 m of phone cable that they replace.
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http://www.skateboardracing.org.au - ASRA, the home of Australian skateboard racing

[bernie]

OK, here is how I did it.

Basic single lane Radio Timer Switch

Components
From www.Netairbuy.com (contact Gao) or www.carymart.com.au
1 x Single channel Wireless Garage door controller
2 x CB-1 long range transmitters

from electronic parts suppliers
Boxes
AA battery holders - 2 x 9volt and 1 x 12volt
2 x 9 volt batteries
20 x AA batteries
3 x Switches
2 x Transistors
2 x Resistors
2 x Capacitors
RJ11 plugs and sockets wires
4 strand or 2 strand telephone lead.
1 x BTS Timer Order BTS Timer Here
or if you must, a DIY modified Electronic stopwatch (this is very tricky for most!)

2 x Tape switches – Greg Ambler pattern – see How to build a Tape Switch here......

Step 1 get a BTS Timer, and you can proceed directly to Step 2!
But if you are too cheap or too poor, or have too much fear of anything from Blacktown, to get a BTS timer....ya cheap bastards...read on.

Open up your imported stop watch, and locate the stop start switch.
Strip back two of the wires in a short length of 4 strand telephone lead.
Solder the wires to each contact of the stop/start switch.
On the other end of the lead, fit a rj12 connector so that the two wires soldered to the stop watch switch are the centre

two leads in the rj12 connector.
(BTS Tape switches and timer also use the centre two wires in the rj12 connectors)
File a little of the watch case so that the telephone cable can pass through the case, but also be firmly held (clamped)

in place when the case is shut.
Re assemble the Stopwatch.

Step 2 – mount the receiver

Mount the wireless receiver in a box with an 8 x AA battery holder (12 volt s), and on/off switch.
Set the transmitter to momentary operation.
Connect a telephone cable to the relay contacts, and on the other end, using an rj 12 connector, and a female to female rj12 adaptor, join that to the stopwatch cable.
Use one of the transmitters to check that the receiver works, and the stopwatch starts and stops each time you press the transmitter button.

Step 3 – make a delay circuit
Because the front wheel of the skateboard, crossing the tape switch will start the timer, and the back wheels will then stop the timer, we need to delay the closed state of the tape switch long enough for the rear wheels to cross the tape switch, so that the timer runs until the front wheels cross the tape switch at the finish of the course. (and also so that the transmitter stays on long enough to trigger the receiver.) This only needs a delay of about 4 seconds.

Using a transistor as a simple "delay" switch.
The delay circuit consists of a 9volt battery, a capacitor, a transistor, and a resistor.
A transistor has three terminals, being the Collector, the Emitter, and the Base. When the base of a transistor is charged, it transforms the connection between Collector and Emitter from an open switch (non-conductor) to a closed switch (conductor). By using a capacitor and a resistor you can keep the base of the transistor charged for a period of time, after the power is disconnected from the circuit. (This is a very basic summary of the use of a transistor as a switch,and ignors the full capabilities of transistors in general but it is all that we need for this application)

Assemble delay circuit

The positive terminal of a 9 volt battery is connected to the capacitor via the tape-switch, The positive terminal of the capacitor is then connected to the base of the transistor via a resistor. When the tape switch is crossed, the battery fills the capacitor instantly, which is slowly discharged via the resistor, into the base of the transistor. The negative terminals of the capacitor and battery are connected to the Collector of the transistor, ie circuit ground. Next join a lead to the emitter of the transistor, and another lead to the collector of the transmitter. These two leads run to the radio transmitter switch.
Exact size and value of resistor and capacitor is determined by the delay that you need, and you can find out suitable values from most electonics books. (failed compact flouro lights, is a good source of free transistors!)

Step 4 Modify the transmitter.

Open the transmitter case, and locate the activation switch on the circuit board. Solder the two leads from the delay circuit to the contacts from the switch. (I used rj12 socket and plug to join the delay circuit to the on switch on the transmitter) Connect the tape switch to the delay circuit and test. The transmitter should stay on for a few seconds.
Next connect the 6 x aa (9volt) battery holder, via some leads and a switch to the battery contacts in the transmitter.

Step 5 Assemble transmitter boxes.

Put the delay circuit and its battery into the box, with a rj12 female socket set into the side of the case. This socket connects the tape-switch to the battery and the capacitor in the delay circuit, using centre two connectors.
Hold components in place with double sided tape.
Connect the delay circuit leads to the transmitter, and put the transmitter and its battery into the case. Then test and close the case.
(note that the transmitter shown is not the CB-1 transmitter, and is using a single 9volt battery for the delay circuit, and another 9 volt battery, mounted behind the transmitter for transmitter power)


this is the preferred CB-1 transmitter, which is what I used in the other box.


Step 6 - set it up and use it

Connect the tape switches, turn everything on, and start racing.

AA batteries give much better duration than the 9volt batteries for the transmitter, and should last about 20 or 30 sessions (guessing, have not run flat yet!).

This setup is good for about 120 metres in a ditch, and about 300 metres in open ground.
The best part is the portability and simplicity of use, with no cables to trip over.

Cost should be under $100.

I used a dual channel controller, for this set-up but unfortunately it does not work for twin lane racing, as the second channel to trigger has to wait until the first channel has stopped receiving. For twin land racing it is best to use two single channel receivers and 4 transmitters.
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LET IT GO....Naaaah second thoughts...Don't Ever Let It GO.....become completely and pointlessly obsessed and learn to love wallowing in your paranoia

[haggy]

Excellent stuff Bernie!

[Fletch]

Your the cleverest accountant ever.

Hope to get my time taken soon
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Tricks are for guys who don't surf.

[Bugs]

Wow, great write-up there!
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http://www.skateboardracing.org.au - ASRA, the home of Australian skateboard racing

[Robbo]

please make me one, please make me one, please make me one, please please please bernie

[GroundHangers]

Burnie, if you use the The BTS timer, i built in a delay of 2.8 seconds under a full 9v charge, a half worn battery will shoot the + cap V out to around 3.3 under normal conditions. Delay can be changed, if you want less delay just change the capacitor to a lower value, i think its at 10 or 8uF at the moment.

[mosu101]

bravo sir!

would deem this as the penultimate design if it used optic gates. However currently I must say its far superior to anything I have been bothered to get of my arse and solder!
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Do evil vegetarians worship Sultanis?

[bernie]

Greg,
On this setup, a delay circuit is needed for each tape switch, because the transmitters need to be held on long enough to get their signal received. 2 - 4 seconds is the range needed. Have tried it with your timer and it works really well. Have sent a note to netairbuy, to see if he will build transmitters with an rj12, and delay circuit.

Mosu, I had seen a design for DIY optic gates, and those laser pointers are excellent value, and should overcome ambient light/heat interference on a hot day, but got short of time, besides Greg's tapes are just too easy to build and use, and more importantly are reliable.

Robbo, would love to help, but the day job is getting in the way, so don't be scared, it's not hard to build!
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LET IT GO....Naaaah second thoughts...Don't Ever Let It GO.....become completely and pointlessly obsessed and learn to love wallowing in your paranoia

[Scuppers]

The heat interference you're referring to..is that a problem for 'infra red' style beams that can take the place of the tape switches??? has anyone tried using infra-red beams ??you can buy ir kits (break the beam..generates a short circuit) at Jaycar for about 20 bucks but if they're no good on a hot day I wont bother

[bernie]

Infra red gets unreliable on hot sunny days.
You also need to mount the sensor in a long tube, painted matt black inside, so that it only has the light source in its line of sight.

Build tapes switches, they are too easy!
_________________
LET IT GO....Naaaah second thoughts...Don't Ever Let It GO.....become completely and pointlessly obsessed and learn to love wallowing in your paranoia

[Scott Tansley]

Wireless. Your a legend Bernie.

[bernie]

here is the delay circuit.


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LET IT GO....Naaaah second thoughts...Don't Ever Let It GO.....become completely and pointlessly obsessed and learn to love wallowing in your paranoia

[Scuppers]

After many months of circuits, soldering, experimenting and expletives a 100% reliable naccos wireless timing system is up and running.


Thanks for the help Bernie..but I have changed the circuit a bit and added an 'early car warning system' function as well.

For the Tech heads this is how I did it.



Bernies delay circuit used a transistor to regulate the flow of current to the transmitter..when I tried it with a transistor the end tape switch transmitter would sometimes cause a click..click.click...click on receiver relay which would start and stop the stopwatch a few times. I reckon this was because the capacitor was dicharging gradually to the power supply cct of the transmitter and maybe the cutoff threshhold voltage wasn't definite enough to cut off the transmitter quickly and totally (ie you culd see the transmitter on full power, then gradually drop off to no power.



By keeping Bernies excellent design but replacing the tranny with a reed swith coil relay the coil (and hence power to transmitter) is either on or off..the coil relay electrically isolates the two parts off the circuit when looking at the transmitter light it's either hard on or off....AND you still get a 2 to 3 second delay which is fine for the front/back wheel issues.



Using the same transmitter I've wired up a small peizo window alarm to the receiver relay..which you attach to your belt..with one repeater half way along the road to give an alarm while bombing a little used single lane road with a few blind corners in the national park..the roads about 2 km long and you get about 1000m coverage so a tape switch at the entrance and one repeater half way along gives you a little more peace of mind...well it's better than nothing.

oh yeah...when you buy the reciever, the arial is about 20cm long but coiled up like around a pencil inside the housing..if you unwind it and leave it hangin out straight you get heaps better reception.

[bernie]

Grass Hopper
Enjoy the pebbles!
_________________
LET IT GO....Naaaah second thoughts...Don't Ever Let It GO.....become completely and pointlessly obsessed and learn to love wallowing in your paranoia