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# Stopwatch, of sorts.

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#### cga1974

##### New Member
I need some help. You'll quickly find I'm not an electrical engineer by any stretch of the imagination. I am a fairly technical guy having been a network engineer for 15 years. My expertise just doesn't lend itself to this particular project.

On weekends I manage a dragstrip (think Pinks). We run two classes of cars, one which allows delay electronics and one that doesn't. The problem we're having is that we believe there are several racers who are cheating in the "no electronics" class by hiding illegal delay devices.

This is the best way I can think of to test the car's transbrake circuit to determine if there is an illegal delay present.

I need to have some sort of stop-watch type circuit accurate to 1/1000 of a second. It needs to be able to start the timer when 12 volts is applied to one pole, and stop the timer when 12 volts is applied to a second pole.

I used Visio to draw a rudimentary wiring diagram of how the timer would be connected to the car.
Blue representing the car's wiring. Red the connections attached to the timer.

So essentially, the timer would have three wires with aligator clips. One would get grounded to the car to complete the circuit. The second wire would connect to the transbrake switch. The third would connect to the transbrake solenoid.

My hope is that when the transbrake switch is closed, the immediate connection to the "start" pole would start the timer. Then, the delayed circuit in the car's electronics would trip the "stop" pole. The timer would then show the amount of delay in that circuit. Any delay over .003 seconds is illegal.

I've searched all over the net for stopwatch circuits. I've found a couple, but nothing accurate to 1/1000 seconds. I also wouldn't know how to start and stop the timer with 12 volts.

You need a very simple adaption of the 2-digit counter on Talking Electronics website.

2Digit up/down Counter

I think the most reliable and easiest way (probably cheaper in the long run too) is to clip on ruggedised standard test equipment. One easy way an oscilloscope, or a Counter/Timer with A/B triggering. Instead of fragile scope probes, make up some sturdy croc-clip leads. Will take some skill at first to set up and use triggering. Many electronic engineers don't know how to trigger a scope, so don't feel bad if it seems daunting. Many scopes have stored setting recall for unskilled users.

TENMA|72-6800|OSCILLOSCOPE, 20MHZ | Farnell United Kingdom

I presume you wish to deploy this in front of the competitor to help you judge if they're cheating. Problem I can see is that they will get round this next time by using a secret hidden 'bypass switch' to bypass the illegal delay timer. I guess you could get round that by doing always doing the test secretly.

Trouble is, it might all get like miltary intelligence, decrypting enemy messages where you learn definately something is going on, but you can't act on the infomation. This problem was in WW2, it bugged the British who decrypted nearly all the Nazi traffic, but couldn't do much with the information because the Axis would suss it and then strengthen their codes! Why I say this, is because if you do catch someone using technology with your technology, at some point you might to need to 'show your hand', if the person denies having technology. So you'll probably need to think on your feet.

Maybe you can develop the rapport and trust you've got with the competitors perhaps suspected of using illegal technology, and get them to help you create a solution with them that will ensure it's a level playing feild for all. Bit like performance enhancing drugs in sport innit!

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You need a very simple adaption of the 2-digit counter on Talking Electronics website.

2Digit up/down Counter

Works for me, but I'd still need to know WHAT this simple adaptions are. I have no idea to how to take that and make it what I need to it be. Can you help with that?

I think the most reliable and easiest way (probably cheaper in the long run too) is to clip on ruggedised standard test equipment. One easy way an oscilloscope, or a Counter/Timer with A/B triggering. Instead of fragile scope probes, make up some sturdy croc-clip leads. Will take some skill at first to set up and use triggering. Many electronic engineers don't know how to trigger a scope, so don't feel bad if it seems daunting. Many scopes have stored setting recall for unskilled users.

TENMA|72-6800|OSCILLOSCOPE, 20MHZ | Farnell United Kingdom

I presume you wish to deploy this in front of the competitor to help you judge if they're cheating. Problem I can see is that they will get round this next time by using a secret hidden 'bypass switch' to bypass the illegal delay timer. I guess you could get round that by doing always doing the test secretly.

Trouble is, it might all get like miltary intelligence, decrypting enemy messages where you learn definately something is going on, but you can't act on the infomation. This problem was in WW2, it bugged the British who decrypted nearly all the Nazi traffic, but couldn't do much with the information because the Axis would suss it and then strengthen their codes! Why I say this, is because if you do catch someone using technology with your technology, at some point you might to need to 'show your hand', if the person denies having technology. So you'll probably need to think on your feet.

Maybe you can develop the rapport and trust you've got with the competitors perhaps suspected of using illegal technology, and get them to help you create a solution with them that will ensure it's a level playing feild for all. Bit like performance enhancing drugs in sport innit!

Ha... I don't have any idea of what you said in the first paragraph. The "counter with A/B triggering" doesn't sound so complicated, but I need more details, either way really, to know what would be involved. That Oscilloscope runs about \$400USD, which is not within the budget for this.

As far as catching them, we figure our best defense against the cheating is psychological. The plan is to start spot checking random cars at different points. We may pull them out of the car right on the starting line or at the end of the track after they've completed the pass. It might be more difficult for them if they don't know when. I think the Oscilloscope would work well here, because they wouldn't understand it and it would likely scare them lol. We actually thought about getting a metal detector wand and waving it around the car like it was scanning for electronics or something.

If you're still with us, Go low - tech

If you only need to take a go/no-go reading, try a pair of standard automotive relays. I'm assuming the solenoid draws a fair amount of current (2A or more).

Connect relay (A) between the trans brake switch and the trans brake solenoid. If they are ever different for any substantial amount of time (it won't be calibrated, but they don't need to know) then relay (A) will pull in momentarily, and relay B latches.

Coil (A) (+), COmmon (A) and COmmon (B) to tb switch,
Coil (A) (-) to tb solenoid.
NO (A) and NO (B) to coil (B) (+).
Coil (B) (-) to GND.

Any horn or light you want in parallel with coil (B).

 You probably want a diode in series with coil (A), to prevent the tb from locking 'on'. [/edit]

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What's a substantial amount of time?

For the 2-Digit Counter, simply take the line from the output of the transbrake switch to the "A" input of the timer and the wire from the solenoid to the "B" input of the 2-Digit Timer.
Make the 2-Digit Tmer increment in miliseconds.

What's a substantial amount of time?
I would guess that automotive relays take 0.005 to 0.020 seconds to energize. You could have somebody calibrate one if you really need precision. But the point is deterrent. Once you bust the guy who's trying to skate on 0.040 everyone should trust your magic. You don't have to tell them that you don't know the diff between 0.004 and 0.010.

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