Please help me with this interesting little circuit with lots of switches

Thread Starter


Joined Dec 21, 2005
Dear all

I am trying to design and finally test a circuit. I know exactly what it needs to do but I'm having great difficutly draghting it and am desperate to prototype it for testing.

ok here it goes.......

In brief it is a 18v battery which powers an 18v motor (garden hedge trimmer size) - that is all i know about the values.

I need there to be two switches to close the circuit, ie. the user has to 'press' both switches at the same time to close the circuit. As soon as one is relased, the circuit breaks.

Here is where it gets a bit more complecated.

Secondly I need some sort of component (ive been told a relay switch is best) which could be used as part of a release mechanism when the power is cut. So imagine a small leaver or pin being at one point when the circuit is closed, but as soon as it is open, the pin moves to another position (like an on/off switch)

Thirdly im trying to understand more about RFID sensors and tags because what i want is to have another switch which simply cuts power to the motor when the rfid tag gets within about 10cm of the motor.

Just to explain the this switch/pin component further - the whole idea is that when the motor is running the device is secured to the users hand, but if the user gets into distress they release the switches to cut the power to the motor and the switch/pin will move allowing the mechanics to release the device from the users hand.

I have attached some sketches of the concept to explain further.

I hope what I have explained makes sense.... if not please let me know ( it seems to make sense in my head, which has be mean something i guess)

... would appreciate any help!!

thanks guys!!




Joined Jun 13, 2007
The switching part is easy, the RFID tag part is considerably more complex and difficult. Perhaps there's a less complex way of detecting the users proximity?

I don't think I'd like to attach this mystery device to MY hand!

Two normally open switches in series with an appropriate voltage and the relay coil will do what you want. Both switches need to be closed in order for the relay to operate. Then you just use the relay switch contacts to switch power on/off to the motor.

Thread Starter


Joined Dec 21, 2005
how does a reed switch work?

Idealy the RFID tag or magnet will not need a power supply so if this reed switch and magnet mechanism can act like that then it should be perfect.

I know very little about rfid but it does sound fairly complex - ideally I need a simple solution with minimal problems.

Also one last thing - what is the component I need for this switch/pin mechanism? I want to try and put some sort of circuit together to see if it works.

Thanks for all your help guys - I really need it.