I want to put together a device that trips one switch when there is ~10lbs of pull on a dog's leash, and another when there is ~30lbs of pull on the leash. I've found digital hanging scales for luggage or fish, and I'm assuming the innards would have a load cell or strain gauge I could interface with an Arduino or something but that seems like the most complicated solution and I was curious if someone had a better idea.
Thanks for any thoughts.

 

An appropriately sized spring in a tube that activates two microswitches?

A gate closing spring may work?

 

Bungee cord.
Dead cheap, readily available, stronger than dogs.

 

Devil is in the details.

How accurately does this force need to be measured?
Just off the top of my head- a metal cylinder with two springs of differing rates, with switches detecting the movement.

 

Go hi tech. Study accelerometers.

 

In the interest of keeping it simple I would consider a generic spring scale and mount a few switches at the 10 and 30 Lb points. As to switches maybe something optical or hall effect placing a tiny magnet on the moving indicator. Obviously you can get elaborate as you choose. I would just use two small hall effect sensors driving a few LEDs powered by a few coin cells.

Ron

 

Assuming there's an actual dog bouncing around on the end of the leash, make sure whatever you use has some filtering or slow response. If using something with too fast response, imagine the dog turns too fast to lick his ass, the wave in the leash could trigger an alarm.

 

Thanks for everyone's responses. Hadn't thought of it but now experimenting with springs in tubes and making progress. Thanks again.