# FSR controlling an electromagnetic lick

Hi all. Very new to this, and no real engineering/electronics background, but I learn fast and follow direction well...
I am trying to have a FSR release a NC electromagnetic lock after a certain force - say 3 N - has been applied to the sensor. I *have searched the forum to no avail. I need help mainly with the coding (assuming this can even be done) but will not turn down any offered schematics.

The lock would be in the locked position when it is getting current, and would release when 3N is placed on the FSR, thereby stopping current flow to the mag lock, +/- 0.2N or so (the force doesn't have to be precise, but it does need to be more than X Newton and less than Y newtons)

I have an Uno R3 and a 5V relay to control the mag lock.

Thanks in advance for any help, and I hope I've given enough info. If not, let me know what other specs you need.

WTF is an FSR? Can you provide links to any parts you mention please?

I'll guess that FSR is Force Sensitive Resistor. If so, look up voltage divider to see circuits you can use with analogRead to get something from it.

Hi, sorry for any confusion. FSR = force sensitive resistor. I'm trying to set up a system so that when a fairly narrow range of force - say between 2.5 and 3.5 newtons - is applied to the FSR, this will cut off the power supply to an electromagnetic lock. If the force is above or below this range, then the mag lock will continue to get power and stay locked. Does that make more sense? And I'm not sure what you meant by pinball coil - how could that do what I'm looking to do as outlined above? Thanks again!

FSR = force sensitive resistor. Like Overview | Force Sensitive Resistor (FSR) | Adafruit Learning System
Trying to set it up so that when a given force range - say, between 2.5 and 3.5 newtons - is applied to the FSR, it will cut off power to an electromagnetic lock. Anything below or above that force range would keep power going to the lock, therefore keeping it locked. Does that help a bit? Thanks!

electromagnetic lock?

This sounds like a simple application that does not need an arduino unless there are other features you havent mentioned.

At 3N the resistance is about 3k; and say 100k when unloaded.
I reckon you could do this with a darlington transisitor or transistor and a FET.

OK, but since I have no idea what a FET and darlington are, and I have *some idea of how the Arduino works, and I actually *have an arduino, can you give me an idea of how to write the code for this application? An electromagnetic lock is magnetized when it gets electricity, from a 12V power source. When the electricity is cut off, the magnet - and therefore the lock - releases. You have seen this, likely, in various "security doors" in hospitals, offices, etc.

Sorry my hint wasnt clearer. I do know what an electromagnetic lock is.
Can you provide a link to the data sheet for the specific electromagnetic lock you propose to use?

This is an example

It DOES make a difference because the supply voltage and current will need to be provided from a seperate power supply from the arduino.

Read out the sensor first an write a sketch to control a relay to switch the power for the lock. It's all writen in the examples. I didn't get you right, with the coil of a pinball you can produce a heavy punch. I tought you need to produce a specific force on something.

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