# How do I build a palm reader circuit using electrodes?

1. Sep 23, 2010

### BananaYanana

Hi everyone,

I am currently doing a project with a group of friends. The project requires us to build a palm reader which uses electrodes to read the hand's impedance and then do the things that the circuit was designed to do.

My group's idea is to build a piano. We use the electrodes as the piano keys, so when a finger touches it, the finger will complete the circuit (with the palm as the reference point).

However, we don't have any idea of how a circuit that contain an electrode looks like, especially if the electrode is aluminum tape (it is easily available and cheaper than most electrodes). So does anyone have a sample of a circuit that contains an electrode, or any reference I should go to? I tried looking in the internet but have found none so far.

Thanks!

2. Sep 23, 2010

### Staff: Mentor

Start by experimenting with a DVM on its resistance setting. What kind of resistances do you measure across palms? Does it matter if the hand is wet or not? In what way does it matter?

You need to be sure to use low voltages (a couple of volts) and current limits when coupling signals to humans.

3. Sep 24, 2010

### MATLABdude

I'd recommend Googling for 'touch circuit'--there are some very simple circuits available which can sense a touch on an electrode (usually, a MOSFET gate being charged up or a circuit being completed, though there are much more sophisticated schemes out there).

As for your actual palm reader, I'd recommend an LED, a random number generator, and a hash table of fortune cookie fortunes!

4. Sep 27, 2010

### BananaYanana

What kind of resistances are there? Basically the project requires us to measure the impedance of our palm... which I guess would include resistance and reactance of the palm.

It does matter if the hand is wet or not, the prof said that it may affect the impedance... however since I want our hands to complete the circuit instead, so I guess the impedance doesn't matter significantly, as long as it allows the current to go through?

How do I experiment with a DVM? So do I just build a simple circuit and try measuring the resistances of the palm?

Thanks for the tips, I'll try it out.

Btw, by palm reader I don't mean it necessarily reads our fortune... it's just a device that reads the palm's impedance and do whatever with that value! :D