Go Down

Topic: Need information on distance sensors and how to accomplish this (Read 1 time) previous topic - next topic


Hi, I'm trying to make a system where someone walks through an area and a timer starts. If they keep walking and then cross a second area, the timer stops. The whole time, this timer is shown on a separate screen. Think of it as a sprinter trying to measure his time over a 50 metre dash.

My current approach is to use 2 Arduinos which communicate with a central computer (Raspberry Pi?) using RF transmitters and receivers. Since the subject will only be walking in one direction and not stopping in the area, I was going to use a distance measuring sensor and start the timer when the distance changes greatly (subject walks in front of Arduino).

Am I approaching this correctly? Would I need something like a Raspberry Pi to receive the communication from the Arduino to start the timer and display it on the screen? Is RF the best communication method for areas that may not have Wi-Fi? Would Bluetooth be better? Thanks.

jack wp

Your description is a bit vague. Is this for timing a runner?
How far from start to finish?
Is this to record for just one person at a time, or more?

Bluetooth only has a range of a few feet (maybe 12 feet).

Give us some more details please.


Sorry about that. It will time 1 runner at a time of variable distances, The distance ( I guess) wouldn't matter because I will have 2 Arduinos, one to start the timer and one to stop it.

jack wp

The distance ( I guess) wouldn't matter

Well, maybe not, but then again.. If you want to use bluetooth, or RF transmitters, or wire, or wifi, or whatever, I think it could matter.
Will this equipment be fixed, or moved around ever week?

Is your question which processor to use, which sensors to use, or which communication media to use between start and finish?


Right now I'm more questioning the sensors I should be using.
The device will be portable so the trainer will unpack it, lay it out on the track and then tell the runner to do some sprints while the times show up on a remote television screen. After an hour he packs it all up and takes it home. So my assumption is I could just use 2 Arduinos with distance sensors and when the runner runs past the first one (sensor points west, he runs north through it) and the time starts. He keeps running, then passes by the second Arduino with distance sensor and the time stops. He comes back and runs it again for a new time.

The distance between the Arduinos will never be no farther than about 70 metres apart so I was thinking RF communication would be best. I do have an Electric Imp with an Impee shield for the Arduino but they may be on tracks without Wi-Fi access. I could get around this by having the trainer use his phone as a mobile hot spot but would prefer to have a solution without an external network requirement. Thus RF. And both Arduinos wouldn't necessarily communicate with one another, they would both send commands to a central place (like a webserver over Wi-Fi or a Raspberry Pi over RF) which would start/stop the timer on the screen.

Lastly, I can really simplify this by saying I'd like to have a runner's time show up live on a screen while training, no more to it than that. Feel free to suggest any hardware you think will accomplish this, I just assumed a couple of Arduinos would be cheapest. These official training kits that do this are available at retail but cost $11,000 and my friend wants to start a training camp so I'm trying to give him something for under $500.

jack wp

With that description, I think I understand what you want to do now.
Distance sensors (ultrasonic) are generally good for about 2-4 foot, so I can see how you can have success with that, if the runner is directed that close to the sensor.

I am not sure of your screen requirements. If you just need the numbers, a small LCD (2 line by 16 characters), driven directly from an arduino may be the answer.

For the communications (rf), I am not familiar with rf modules for arduino, but I think you can find a pair that will exceed the 70 meter distance.

I think you could do the system with  two arduinos. 

What do you think? What questions do you still have?


Just looking for advice to make sure I'm on the right track really, I have no problem writing a remote script to start a timer when it receives a signal and I don't think it'll be hard to set up an Arduino so it triggers when someone runs by it. I just want to make sure I'm using optimal resources for communicating back to the time starter (computer) to tell it to start.
I guess I do have one more question, the RF transmitters and receivers are less than $5 each so that's not a problem but all the ones I see are broken out onto breadboards. I don't want that, are there any proper RF communication shields specifically for plugging directly into the Arduino? I don't want an extra breadboard.

Go Up