Let's Make Robots!

Help with smoking pot(s)

Well, I thought this would be simple, I'm a bit embarrassed really. I was hooking up a simple 5k potentiometer to one of the ADC inputs of a picaxe28. I had +5v to one terminal gnd to the other outside terminal and signal to the center pin. I used readadc and a debug and the set-up worked and did what I needed, however after about 20 seconds came the evil blue smoke. What did I miss? Man, I feel like an idiot -such a simple thing to hook up. Any ideas?

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I would first like to appologize to everyone for wasting you guys' time. Yup, it was a stupid, simple problem...

Grog -you got it! Much love to you.

So here's the deal AND IMPORTANT INFO TO EVERYONE USING THE 28 BOARD!!!

*****Note*******

The ADC inputs on the 28 board are set up a little funny. (And I should have remembered this from the time I fried my sharp sensors)

Ground is on the INSIDE!

Hot is on the OUTSIDE!

And....... 

SIGNAL IN IN THE MIDDLE!! --THE MIDDLE I SAY!!!

So I guess this is a lesson to all:

Allways check your pins. Especially if you use servo connectors as the red turns into the signal wire and orange is V+.

_______________________________________

Well, I'm going to chalk this up to a learning experience. Thank you, thank you all for helping me! Much Love.

 

C the C 

Now, why are you giving GroG the credit?

I wrote:  +/- to either side, ADC in middle

I want that credit from GroG!

GEEZE - YOU TURNED INTO QUITE THE MEGLOMANIAC !

BUT I'LL STILL GIVE YOU MUCH LOVE !

PS - My diagram was prettier ! 

GroG
my robots
my garden

The typical radio shack pot is on average 1/4 watt, as anachrocomputer explained the resistance value (5K or 10K) makes no difference on how much current the pot can handle.

Just take a resistance meter and measure the different points of the pot as you turn the knob. It should become very apparent quickly which pins are which (signal will always be one of them if it changes - so will be able to isolate signal very quckly - e.g. test 2 pins, move the knob, if the value changes one of the pins is signal - test the untested pin and one of the pins you have tested if it moves when you move the knob then the pin which was in both tests is the signal). Then measure your source voltage and the ADC voltage value.

It sounds like you might have accidently connected the potsignal to ground (that could explain the short), and your making a fixed resistance bridge with the resistors you've added.

GroG
my robots
my garden

Glad to hear that you've found the source of the problem!

Oh, and thinking about the audio vs linear taper thing, with a linear pot, you should get a reading from the ADC of about 128 with the pot in mid-position.  And 0 at one end, and 255 at the other.  Which is probably what you'd want.  With an audio taper, you wouldn't get 128 in mid-position. Incidentally, here in England, we call it a log pot or a linear pot (that's log, short for logarithmic).

How about this for a safe(r) pot usage (on the right with 2 dangerous wiper positions, compared to the left) :

paint drawing of potentiometer use

 Just add a resistor to the wiper, and it would limit the current. Probably a 500 ohm or 1k is all needed.

 

Dave