Device for touching a touch screen?

I need a type of solenoid/servo device capable of moving a few millimeters at a fast speed. I am building a device that will tap a touchscreen for me via an electric signal (In this case, and arduino.) they need to be relatively cheap and small. I will have four of them evenly spaced over four inches (They need to be no wider than an inch, would much prefer they be less than a half inch in width. Height isn't important, and length should also be under an inch.) They also need to be fairly weak, i dont want one of them punching a hole in my tablets screen by accident. Doesn't need to be controlled by PWM, either off (Not touching) or on (Touching) will work fine.
Please do leave links along with the name of the device/part.

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rickharris3 years ago

As many ways to do this as you can imagine - Depending on your skill, budget, expectations and what fast actually means to you.

The illustration shows how I might do it if i wanted to replicate finger tapping.

RocketPenguin (author)  rickharris3 years ago

That's quite an ingenious plan, only issue is, there isn't enough space for such contraption! Indeed it would be fast, the moment it touches it immediately releases, but i have to have four of these fit onto a 3D printed frame right next to each other, along with a photoresistor embedded alongside each tapping device.I will be using a galaxy tab pro 8.4" tablet, which only gives me about four inches in portrait mode. Thanks for the brilliant idea, and if all as fails, i may just print it out and go for it, but i would rather prefer something more simplistic, and quite a bit smaller.

Thanks for the reply!

Lots of ways to make it smaller.

Use small toy motors or even tiny pager motors, replace electromagnet with a small wheel with another perm magnet stuck on it. N to N so as the wheel turns the magnets repel and lift the stylus.

Use popsicle sticks and small magnets to load can be small if you ballance the stylus.

TAPPER 2.jpg
RocketPenguin (author)  rickharris3 years ago

If i understand your concept correctly, wouldn't it be difficult to have it tap the screen only once? Wouldnt the motor continue rotating, and cause it to tap the screen multiple times?

Only if you let the motor continue. A small geared motor if very cheap to give a slower rotation so you can easily control the tapping speed with a switch or a micro-controller.

You see there are LOTs of questions a designer would ask about what your trying to do to design a full and usable solution like:

How fast do you want to tap

How many times

What is the speed, tap rate and positional accuracy required

How much forces is required

Are you able to use a micro controller

What is the budget

And possibly a lot more.

RocketPenguin (author)  rickharris3 years ago

Tap speed: Needs to move two millimeters in a 1/12 of a second

Amount of times: As frequently as needed. may need to tap 6 times in one second.

Speed: As said above. the device is stationary, whatever needs to be tapped will be in the same physical position on the screen.

Force: None. A touchscreen such as mine doesn't even require me to touch the screen, all i need to do is hover a maximum of 1/64 of an inch above it. Point said, the force would be equivalent to me dropping a sheet of paper.

What controls it: An arduino.

Budget: Would prefer each unit be under 5$ (Servos can be more than that, but solenoids fit in the range, along with a lot of other devices in such size.)

Anything else?

Then you already have your answer - The relay system. - Any electromechanical system will be similiar.

If your not happy with the relays then your going to have to go for the mechanical solution and work out how to make it fit your needs.

You have a limited number of actuators available to make the real world movement:

An electro magnet (basically what the relay is

A linear actuator

A mechanical cam and lever (which my magnet design is.

To adjust tap rate your going to need to use switches and do it manually, adjust the speed of the motor or use a micro-controller - Picaxe, Arduino, Raspberry pi, Beagle bone etc.

RocketPenguin (author)  rickharris3 years ago

The entire device will be powered via Arduino, and thus delay(); will be used.

Roby912 years ago

This is the simpliest way actually..


otherwise u could use Android ADB commands..

RocketPenguin (author) 3 years ago
RocketPenguin (author)  RocketPenguin3 years ago

HUUUUURRRGGGGHHHHH This doesnt actually work with my tablet. The copper is conductive, and thus acts as my finger, with or without charge.

敏王3 years ago


Is it something like this?


RocketPenguin (author)  tgferreira1843 years ago

Then i saw this:

I would prefer using something other than relays... then again, it may be the best idea yet. There just isnt a way of mounting them...

RocketPenguin (author)  tgferreira1843 years ago

Thats actually exactly what i had in mind.... Why didn't i find this before.... Ugh. Oh well. I shall still do it, but better, with 3D printed frame and more efficient motors/servos/solenoids. My idea has been stolen by someone who has previously thought of it. :P Thanks for sharing this beam of light with me.