Decoding rotary switches

[mister_e]

You can probably use 1 ADC line for each rotary switch (or mix all of them, then feed it to a single ADC input). Basically you convert BCD to voltage with R2R resistor ladder, then you feed this output to your PIC.

Hardware technique
http://ww1.microchip.com/downloads/e...tes/00234a.pdf

8-pin PIC - Tips 'n Tricks
http://ww1.microchip.com/downloads/e...doc/40040b.pdf

[aratti]

The rotary switch should have a common plus four outs (bits). If this is the case then connect all the bits of the three rotary in parallel, using diodes, (total 12) and feed four pic pins inputs (better Rb0; Rb1; Rb2 and Rb3). Activate the internal pullup and connect Rb4; Rb5 and Rb6 (outputs) to the commons of the rotary switches .

Set high Rb4; Rb5; and Rb6. Scan the rotary setting to low Rb4 and read the first rotary switch, set high Rb4 and Low Rb5 and read the second rotary etc.

Your true reading will be 15-x; where x is the pic reading. If you want a direct reading you have to pulldown the input pins, reverse the diodes and reverse the scanning outputs level.

Al.

[timmers]

.... or use a parallel in serial out shift register. By cascading several registers you can have as many inputs/outputs as you like.

Tim.

[AndrewC]

Steve:

Figure 3 illustrates a resistor network, which changes a
4x4 keypad into a switchable resistor matrix. The
resulting resistance is read by an ADC or a capacitor
charge timer, which determines the key that is pressed.
This is practical only when one key is pressed at a time.

... so that doesn't really work in this case, but those are good links from Microchip, thanks

Al: I think the usual solution is to use diodes like you say.

Tim: I'll have to think about that

Thanks for the inputs

Andrew

[mister_e]

So I haven't explain it correctly then... and i wasn't refer to a 4x4 matrix directly but multiple switch with a single I/O and a single (or multiple) ADC channel. Food for thoughts

[AndrewC]

Actually this is really one of those situations where I'm trying to force a solution to a problem - I picked up a bag of these switches for a couple of dollars and now I'm looking for a use. The application is just to provide a knob to control the duty cycle of three different PWM module. The easiest solution is just using a pot and an ADC channel - three pins, some case commands and it's done.

Sometimes one's head gets lost in a dark place !

Andrew