Hi everyone.
Am trying to build a stopwatch to time horse races in Mexico.
I currently do the fotofinish with a laser trigger that when horse blocks the signal (wich is emited to a photodiode) another instrument reverses the signal and fires the camera tru the shutter release conection, but I want to ad the timing and I have fount a table stopwatch with banana jacks for external triggering wich I think will work for my proyect, if I put a split cable ( Y ) on the instrument that reverses the signal that way when horse blocks laser light I will have signal to camera and to the stopwatch to stop timing, up to this point I think am still good, but my problem is that I dont know how to start timing from the gates wich are far away, it has to be wireless when the gates open I need something to send a signal to the stopwatch to start timing, the distances vary from 100 - 350 yards.
If theres anyone that could help me please, as you notice I do not have any electrical skills at all so please take it easy on me.

Thank you all.

Guill.

 

Adapt a wireless doorbell.
Laser and photodiode to trigger transmitter.
Have the receiver start the watch by a trigger circuit.

 

Be aware that because of the coded transmission in these doorbells there can be a significant (100-200mS) delay between pushing the button, and the receiver responding. For photo finishes, that might be too much.

ken

__________________
"To invent, you need a good imagination and a pile of junk."
Thomas A. Edison (1847 - 1931)

 

what about an FM transmitter transmitting DTMF
receiver se up to trigger on the DTMF signal
THEN figure out how much delay you have and then compute for actual time.
OR
have a Laser at start gate aimed at the finish line receiver.
would have to be a pretty good Laser but do-able.
wonder how far away a Laser can be detected.

 

I already have the laser system working fine at the finish line the pics are coming perfect no delays,
the problem is that now i need to ad timing i can sto the stopwatch at the finish line with the system that i already go but i just dont know how to start the stop watch at the gates wich are 350 yards away from me.
It needs to be wireless signal to where the finishline is.

 

one more thing, i forgot to mention that at this places i dont have acces to ac power, it all works with batteries

 

aimed at the finish line receiver.
the Laser then sends a trigger pulse FROM the start gate TO the finish line.
problem is any movement or dirt may affect the trigger.
I would opt for the FM transmitter w/ DTMF signal.
Big deal if there is a slight delay.
so its a slow track?

 

I think this fm transmitter could work, could you tell me how it works?

 

The laser pulse will not work because theres a lots of people and threes around.

But the fm might.

And the track is fast horses run on average of 43 miles per hr. ofcourse they only race about 15 seconds

 

the start gate triggers the DTMF signal (transmitter already transmitting a null signal)
As soon as the start gate opens the DTMF signal is transmitted to the receiver which is already receiving a null signal
as soon as the DTMF signal is detected the stopwatch is triggered on.
DTMF is what the phone company uses. I believe there are 16 frequencies that are used w/ 16 additional frequencies included.
listen to your phone receiver and press a button. Thats what DTMF sounds like.
IMO the DTMF would be more reliable than just a simple beep or other sound the transmitter sends out.
do a search for DTMF circuits

 

The doorbell system I had in mind is a cheap Chinese product. No fancy encoding. I thought it would work because there will be no wireless doorbells at the track.

On the other (more professional) hand...
Dual tone encoders and decoders are sold prebuilt on little circuit boards. They are cool and easy to use.
If you go this route you might want to use crystal controlled transmitters and receivers.
Better hobby stores sell good devices for planes, boats, etc.

 

foringa was talking about distances of 100 to 350 yards. I doubt that any "cheap Chinese" doorbell will work at distance of over 1000 feet. The ones I have spec 150 feet.

ken

__________________
"To invent, you need a good imagination and a pile of junk."
Thomas A. Edison (1847 - 1931)

 

I have been reading on it but am so confused now, it seems to me that two walki talkies with a signal transformer from dtmf-bcd on one and a trigger switch on the other will work.
Is this correct?

 

as long as there isn't alot of traffic on the channel you select.
there are IC's that do all the DTMF stuff. All on one chip.
you just need to build it.
I looked at Ramsey Electronic kits - has possibilities

 

I this kit at Ramsey Electronics (WTS1C wireless trip sensor ) that comes with a UHf transmitter that can transmit up to 300' away to the receiver but if theres a signal repeater or signal booster I think this could work.
Whats your opinion?