finger touch

Started by aila May 31, 2010
hi all
I have a problem using finger touch switches
I want to use a number of these switches but I have limited adc pins on my micro. I searched the net and I found LM2907 but in fact I couldn't realize how it works. Can anybody help me to use these switches? I prefer to have reliable digital outputs
thanks in advance
Aila

Hi aila
you can use 4067 (multiplexer) instead of LM2907
this IC need 4 pins for address and also 1 pin for out put, you connect these 4 to each pin from each port you want and connect the out put pin (is written z in data sheet) to 1 pin from your ADC port, and the switches are connecting to other pins of 4067, then you can read all outputs by programming your micro chip make these 4 address pins 0 and 1. you can also use more micro by connecting them by I2C protocol or other ways, but using 4067 is the easiest I've tried.
Niloofar

________________________________
From: aila
To: a...
Sent: Sun, May 30, 2010 11:31:39 AM
Subject: [AVR club] finger touch

hi all
I have a problem using finger touch switches
I want to use a number of these switches but I have limited adc pins on my micro. I searched the net and I found LM2907 but in fact I couldn't realize how it works. Can anybody help me to use these switches? I prefer to have reliable digital outputs
thanks in advance
Aila



________________________________
From: niloofar zendehdel
To: a...
Sent: Tue, June 1, 2010 3:37:53 PM
Subject: Re: [AVR club] finger touch

 
Hi aila
you can use 4067 (multiplexer) instead of LM2907
this IC need 4 pins for address and also 1 pin for out put, you connect these 4 to each pin from each port you want and connect the out put pin (is written z in data sheet) to 1 pin from your ADC port, and the switches are connecting to other pins of 4067, then you can read all outputs by programming your micro chip make these 4 address pins 0 and 1. you can also use more micro by connecting them by I2C protocol or other ways, but using 4067 is the easiest I've tried.
Niloofar

________________________________
From: aila
To: a...
Sent: Sun, May 30, 2010 11:31:39 AM
Subject: [AVR club] finger touch

hi all
I have a problem using finger touch switches
I want to use a number of these switches but I have limited adc pins on my micro. I searched the net and I found LM2907 but in fact I couldn't realize how it works. Can anybody help me to use these switches? I prefer to have reliable digital outputs
thanks in advance
Aila



Hi Niloofar
thanks for your answer. I have used 4067 and 4051 in my projects and I know how they works. but the problem is ,I don't know what is the best way for reading touch and proximity switches. they act as capacitance . I don't know what is the best way for measurenet their capacitance. also 4051 is not safe against noise and this is a big drawback.
Thanks
Aila




Read this aplication note from microchip.

http://ww1.microchip.com/downloads/en/AppNotes/01298A.pdf

I test this form on 2 o 3 microchip micros and works well.

2010/5/30 aila

> hi all
> I have a problem using finger touch switches
> I want to use a number of these switches but I have limited adc pins on my
> micro. I searched the net and I found LM2907 but in fact I couldn't realize
> how it works. Can anybody help me to use these switches? I prefer to have
> reliable digital outputs
> thanks in advance
> Aila
>
>
>

--
Un saludo
Enrique Aguilar.