Thread: Simple Diode question....

ok would it be possible to use a diode for connecting multiple lines without them actually touching like the below image.

I want to tie some lines together to determine if any 1 line went high. So if 1 line went high then i know to check them all to see which one it was.

To determine if HIGH i check output on the after diode... To determine which one went high i check the TP (test point) on the before diode

would this work?

heh... The main thing i need to do is make a INTERRUPT type situation. Where i have 5 buttons pulled low...

I want to use 1 interrupt line on a pic... Now using the schem i made above i will connect the diode output to the pic and the other lines to the buttons so when you press any button.... the output (interrupt) line goes high telling me to poll the buttons which then i can check the TP RA0-RA5 for which went high.. This way i save on interrupt lines....

You get it?

Thats the thing. Nothing yet. Its theory right not.

Im going to post a schematic in a minute im sure you will like

Ok here is what i have in mind tell me your thoughts...



Ok since the 74xx166 has a latch which is active low i will use a NPN transistor to connect it to gnd when a button is pressed. It is pulled high when not in use...

Now when the user presses a button which is pulled low... the line goes high and also sets the latch and the Interrupt line to the pic. Which then the pic will read the latched data using the serial wires con the Jumper (TO PIC)

Does this sound like it will work?

This was made out of boredom and the issue is the max pins on a pic i plan to deal with is 40 PIN. Now the issue with that is that im sure i will be in need of pins... The issue is if i have 8 buttons i dont want to waste a whole port on it. I rather have some type of expansion....

My question is..... is the above doable? Do you think with your knowledge it will work?

What are you making? It looks like a keyboard matrix sorta. You can use a '373 data latch to detect a high. In a KeyBrd matrix the processor pulls all columns (X,Y graph) high that feed to the switches (keys) then reads the rows to see if any are high. If so, then it turns on individual columns and reads the data latch. If not high it turns off that column and turns on the next until it finds the high. Then by the processor knowing which data line on the latch is high it can use a look-up table to determine which key was pressed.

It's all done in the interrupt. So any key pressed will trigger the interrupt.

ok the main idea came from a NES controller but i noticed it was a poll system and interrupt would be better in my case...

NES SNES Famicom Controllers!

I want to be able to test either buttons or other devices like this. Meaning all will be treated as a interrupt and still have there own lines on 74xx166 so i can read the data easy

heh that sounds simple enough but i still prefer this method since there is no need to have a lookup table since the data recieved is 1 byte.

Im sure i could make a simple 4x4 pad...