Let's Make Robots!

You as a sensor?

Quick question... I want to make sort of a "person switch". Two contacts, where each person would place one finger each on one of the contacts then when these two people would touch each other the circuit is completed. Now, I have not done any preliminary work on this at all --I havn't even measure-thingy'ed myself yet (I would assume we have to be talking some pretty major resistance here). --This would be going into a ADC channel of a picaxe and could use the 10-bit ADC if needed for acuracy.  Oh, and if it is not too much to ask, I want the least number of parts and it can't kill you when you use it.


Anyone have any starting thoughts here? --Transistors? Op-amps? Mayonnaise?

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
i am not sure it would work for what you are doing but maybe you could use two of these? http://futurlec.com/Others/QT110.shtml

Did you consider the capacitive direction.

cap1 example

cap2 example

If you use this method direction then the sensing will start working (analog signal) even before the people actually make contact.

ie each person will be connected to one separate plates of an effective capacitor.

At my school we used to have a model where you could put your hands on and it would measure amps I think. There were two handplates of different metals one was copper, I think the other was aluminium, but I don't know. You could use some kind of human battery circuit and use the measured amount to trigger whatever in your code. 

Here are some links i've found about this: 




When I read the heading I thought this would be one of those internet personality checks. You know where you answer a few questions and at the end you find out which star wars character you are or something.

I wanted to know if I was a sharp IR or an ultrasonic sensor or maybe just a bump switch :D

One darlingdon transistor and ~500k resistor for pullup/down. Finger goes between base and +5, collector to +5 and emitter to ADC. Pulldown resistor from ADC to ground.

Here are projects that deal with the resistance through a person'n body.

Draw DIO lets you draw a circuit in pencil on paper and then use it as a musical synthesizer. Plenty of variations are possible. Including "drawing" through your skin.

Make Mag. has an electrical wristband that "detects" truth or lies. By measuring skin resistance.

This commercial kit by Apogee claims to do the same.

Of course none of these claim to detect two persons touching each other. But you are creative...

Yes you will have high resistance and it will vary greatly dependig not only on the people but on other factors such as how dry a persons skin is.

The simplest way will probably be to connect the analog input to ground by a 39K resistor. The analog input is one contact and the +V is the other contact.

A persons skin resistace can vary from 5K-25K depending on many factors. The person/people and the 39K resistor form a voltage divider.