Reading 8 way dip switch

[max]

Hi,
How to read a 8 way dip sw with uC using minimum number of i/o pins and
without using any ic.

tia

[leptro]

here are some ideas:

Multiplexing the switches like matrix keyb-->increase pcb routing difficulty

using diodes and sharing pin with other peripheric components.

or using (not wanted but usefull ) is shift register ic and you will need only 2 lines of your µc.

regards.

[Parmin]

Use increasing size resistor on each of the dip switch leg eg 1k on sw1, 2k on sw2 ,3.9K on sw3 ,8.2K on sw4 etc. and then add the value an read it on an analog U/C pin.

Remember the resistor addition rule 1/R = 1/R1 + 1/R2 etc.
if for example you have sw 1 and 3 on then the value would be 1/(1/1 + 1/3.9)

If you dont have analog uc pin then add a capacitor on the pin and measure the time it took to discharge or charge the capacitor on a digital uc pin.

You only need 1 uc pin.

[max]

I have found a circuit which can be used to read 12 switches using 4 io pins.
See attached sch.
To read the switch apply voltage to a row, read the inputs on other rows.

[titi]

Hello,

This an other way to read switches from one ADC input.

When you push a switch you change the divide ratio, so the voltage is different for each switch.

After the simplest way is to display the value of ADC on LCD by exemple and for each button make this:

Example: the value read is 426 for Button 4.

if (ADC_Value>400) AND (ADC_Value<450) THEN 'Button=4
....

Best Regards.

[pickit2]

Why not ask a few questions
1. is the DIP SW common to GND.
2. what voltage is DIP SW connected to 5+V or more
and then Do you know what a DIP SW is?
http://www.anykits.com/catalog/popup_image.php?pID=353

and the answer is still one input