Hardware recommendations for a timing gate

Other Hardware General Electronics
1

Hello,

I'm currently building a timing system for my wife who takes part in veteran athletics.
She's absolutely obsessed with sprinting and I would get major brownie points for building a system that is more reliable than her freelap (which only works 40% of the time).

I've made a wee prototype that uses the classic HC-SR04 Ultrasonic sensor to detect running past the finish line. The trouble is my wife is so fast that it only picks up that there is someone within 100cm off the sensor about 30 percent of the time.

I'm super impressed that a £2.00 piece of hardware can do this, but I'm looking for a more reliable solution.

My questions for all you big brains are:

  1. More expensive ultrasonic sensors, are they more reliable and do you think they would detect something moving at speed through the field? (my wife runs about a 14.6s 100m (she's 52!))
  2. Am I barking up the wrong tree using an ultrasonic sensor. Should I use something like a laser trip wire? I'm worried that this wouldn't work in the sunshine (apologies I'm a total noob at this).

Thanks so much for all you help.
Loving the arduino so far, such a laugh.
Mark

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2

Depends if there are bats in the tree. Heh heh.

Typically a light beam break sensor would work better for this.

3

The laser sensor or photoresistor is usually placed inside a tube / black box or something similar to avoid ambient light, in this way optimal results are obtained in almost any situation.

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4

and you can modulate the beam to increase ambient light rejection.

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5

Amazing thank so so much everyone!
Any recommendations for Lasers? Has to work over a distance of 1m.
Great idea about the photoresistor in a black box! Totally never occured to me!

6

I suggest a photo transistor or photo diode, not a photo resistor. Those are slow and don't have a spectral response close to a red laser chroma.

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7

https://es.aliexpress.com/item/1005003480436168.html

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8

I agree with @anon57585045.

Laser sounds cool but not needed over such short distance. IR LEDs and IR receivers would be my suggestion. These are normally used for A/V remote controls but can equally be used for beam-break applications and have the advantage that the light can be modulated to match the receiver, which as mentioned above, really helps with rejecting ambient IR light. Natural IR light is not modulated at 38KHz or whatever, so the modulated light stands out like a sore thumb, to an IR receiver, even in bright daylight, because they are highly sensitive to only that 38KHz signal.

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9

...and the hardware is cheap, easy to set up, and reliable. With a laser, you have the problem of aiming the thing. You don't really need that over such a short distance so a broad emitter is fine.

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10

A 1 cn wide silk ribbon stitched with a conductive thread and held by two conductive clamps that exert only the necessary pressure for electrical contact, would make the finish line more real and would avoid complicated sensors and code.

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11

I would really really get brownie points for that!

12

Brilliant, thanks everyone IR receiver and emitter it is.
Going to make a breakbeam I think, rather than the ones that are all in one.

Cannot believe how helpful everyone has been. Thank you so so much

13

Yes, don't use them.

A common IR diode and 3-pin 38kHz receiver is much easier to use.
I had a working setup that bridged ~50m in broad daylight.
Beam thickness was about 5mm and reaction time 1/1000 sec.
Leo..

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14

Note that practical systems generally use lenses or focusing mirrors.

Mirrors work better for IR.

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15

Hello
Take a view here to get an idea for the housing:

Have a nice day and enjoy programming in C++ and learning.
MIND THE GAP

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16

Thanks Paul,
Loads of good ideas in there.
I'm building the case in Tinkercad.
Honestly arduino and 3d printing is like I've arrived in the future.
Having such a good time (this community making it even better, thanks all of you for being so lovely and welcoming!)

17

I like it but what about the return wire?

18

Your Idea Is very interesting ,I've faced the same problem once and i used this Laser trip wire
and Sorry if i'm wrong

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19

It goes on the same tape, the clamp opposite the mcu closes the circuit.
The clamp on the mcu side does not close the circuit, it makes separate connections to the lead wires.
The lead wire is the usual one used for projects with the Arduino LilyPad

20

And if by chance there are more than two runners, (to invite a friend for example), passing through the finish line, in addition to stopping the stopwatch, activates ESP32 CAM and we obtain a photo finish.

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