Potentiometer problems

[be80be]

You all really don't think if pot A wiper to positive and pot B wiper to ground doesn't look like a short thats without any resistors on the wiper or the grounds.
Tell my power supply to shut up it kicks the breaker and starts beeping.
but all not lost I just added one resistor to limit the it too a safe level the adc reads fine I think it has to be when it changes pins the clamping diodes has to be it.
I never had this happen with a pic chip. But it did with the first joy stick I put together it had 1 k pot's the one I'm using now has 10 k. The board I removed the joy sticks from was feeding the adc with op amp not right off the wiper.

 

[be80be]

What i was playing with. As you can see the dang thing jumps around It don't now that the pots has a limit of 5mA max to ground

 

[Ian Rogers]

Burt! I'm not teaching you to suck eggs, but are you sure the wiper is connected to the ADC??? The only way you can get a short is if the wiper is on + and one of the end tracks is ground (or visa versa)...

 

[be80be]

LOL it's on the adc something happens when it changes channels from A0 to A1 like i said wiper A is at positive wiper B is at ground some how when it changes it shorts maybe I know it shorts cause the power goes off on the supply its not shorted long but it did short and its thew the wiper and the adc pins after adding a 1 k it no longer happens. I didn't think that could happen.
It don't happen with joy sticks that use 10 k pots.

 

[dr pepper]

That being the case might be better 1k in series with the micro 5v, so long as the rail doesnt dip enough to effect a reset.

 

[be80be]

It can't be the adc I looked at the data sheet pin switching is like 700 nS It works fine after I added the 1 K. I just can't believe the power supply can catch it and shut off. I did some test and its easy to have one pot at ground and one at positive. But I'm thinking it was stalling the motor too.

 

[Nigel Goodwin]

It can't be the adc I looked at the data sheet pin switching is like 700 nS It works fine after I added the 1 K. I just can't believe the power supply can catch it and shut off. I did some test and its easy to have one pot at ground and one at positive. But I'm thinking it was stalling the motor too.

You must have something wired wrong somewhere?, there's no way that the pots can short the supply wired like that.

However, it would be nicer to have series resistors feeding the PIC analogue inputs.

 

[be80be]

See I and see the pot readings I was sending them out serial but that can't be the problem I read the atmega data sheet and i think it be impossible too for that to be happening I think the mini servo was stalling at the same time the pots hit ground and positive. And adding the 1 k stops the servo from hitting the stop and stalling. What has me worried is that adding more sicks make them draw more power. I have four with the 10k pots and four with 1 k pots the 10k are what Im going to use.

 

[Rich D.]

This is not like some kind of unusual art going on here. This is well understood technology used millions of times over all over the world. Nothing here should be so mysterious or unpredictable. I'd bet good money there is a short or some other wiring problem going on here. Maybe a defective pot allows the wiper to contact a grounded metal shell? I think if you carefully examined the result of each joystick individually, you will find some sort of interaction that can identify a shorted condition or a high-resistance short.

Four 10K pots in parallel will only draw 2mA...I don't know of any power supply that can't handle 2 mA! Even four 1K pots will only draw 20mA.

If you have it working to your satisfaction then I guess it's done, but I think something in there is still wrong.

 

[be80be]

It's a art come on they make new ones every day that's better then the old ones. I said in 12 post I changes sticks to ones with 10 k pots the first joysticks had 1 k pots and yes they would be a problem because of there paralleled anyway you look at it here 8 resistors stacked up on the power rail and that's 40 mA load plus a wifi chip that uses up to 350 mA then the servos it all adds up so the 10k is better. I know that this is not new but I didn't have any bad pot bad wiring bad anything and the serial output showed that one wiper was on ground and one on positive when it tripped. So i fixed that problem can't happen and while I fixed that I changed sticks with better one's.
Oh and I ask on here to see if I'm crazy cause I couldn't believe the adc can short. And I wan't to see if anyone had this happen.

 

[be80be]

If you have it working to your satisfaction then I guess it's done, but I think something in there is still wrong.

I think I found that it's in post 28

And adding the 1 k stops the servo from hitting the stop and stalling.

I think the servo stalled when the pot A hit 0 and pot B hit 1023 it makes then hit the stop and grind. They can't hit the stop now I fixed that. I can't hear good I never thought about them stalling. My daughter told me that It was grinding when it happen. Too.

 

[dr pepper]

Cheaper servo's dont have any kind of end limit, if you apply pwm thats off the end of the servo it'll drive the o/p shaft against the end stopand stall the motor, you need software endstops.

 

[be80be]

Cheaper servo's dont have any kind of end limit, if you apply pwm thats off the end of the servo it'll drive the o/p shaft against the end stopand stall the motor, you need software endstops.

I'm thinking that's what happen they went to far and hit the block inside that stops them and it just so happen at the same time it read 0 on A0 and 1023 on A1 lol. I done added software settings

 

[dr pepper]

Either restrict the pwm values by trial and error, or if you want to be posh measure the current of the servo's using a resistor and the adc to detect a stall.

I have a laser cut plywood pan & tilt kit from hobbyking, nice and neat.

 

[Dr_Doggy]

Also sometimes my servos stop 1 step under the inputted pulse(random positions), in effect the servo jitters cause it never makes it to that spot, I in addition had to add a software counter to clear the pwm pulses after 15 - 20 pulses after initial instruction.

 

[jpanhalt]

Also sometimes my servos stop 1 step under the inputted pulse(random positions), in effect the servo jitters cause it never makes it to that spot, I in addition had to add a software counter to clear the pwm pulses after 15 - 20 pulses after initial instruction.

I have worked with servos for quite awhile and cannot relate to those problems at all.

Re: Stopping short of the command point. That can be a mechanical thing (e.g, friction) or electronic. What was your minimum step increment and what was the dead band for your servo? Was there a dynamic force on whatever was being moved, such as aerodynamic forces on a control surface?

Re: Having to clear the pulses after 12-20 pulses ( i.e., about 1 second). I have never seen that to be the case. Can you explain the conditions that make that necessary in more detail?

John

 

[Dr_Doggy]

9g servo, a small load, no caps, running under pickit power
in lower current supply conditions

 

[be80be]

I just put a big cap on it big cap more like a battery size cap works good when it needs that little extra current.

 

[jpanhalt]

PK2 and 3 have very limited power. It is widely believed to be about 30 mA maximum. In fact, some chips, e.g., 12F683, can pose a programming problem alone when supplied at a full 5V from the PK3.

be80be : Good to hear that.

John

 

[be80be]

The big cap works kind of like rolling a car that first gear went out off you get a boost to get going. All joke aside it charges up and gives the needed power.
I started doing it with them esp8266. It gives you a bigger supply for a short time. I got the idea from them supper caps.