Possible Over Current- too many switches
Bill C Cooley
Posts: 18
Hello Everyone,
My project includes 9 switches, more importantly 9 paths to ground. With 1 resister, 100 Ohms, between the switch and the propeller pin and another,10K, from the switch to ground...9 times, parallel to each other. I believe that's a total of .003 amps that's being drawn before anything even happens. Am I right? Is that an issue? Can I use more than 10K and still keep ground in sight? Is there another way to deal with 9 switches? I think I lost the 3.3v on my project board in the first millisecond for this reason. After I soldered 18 resisters on my board so beautifully!
I will have better, more interesting, questions soon. I'm learning, ever so slowly.
Thanks for all your Insight, knowledge, Assistance it's invaluable.
Bill Cooley
My project includes 9 switches, more importantly 9 paths to ground. With 1 resister, 100 Ohms, between the switch and the propeller pin and another,10K, from the switch to ground...9 times, parallel to each other. I believe that's a total of .003 amps that's being drawn before anything even happens. Am I right? Is that an issue? Can I use more than 10K and still keep ground in sight? Is there another way to deal with 9 switches? I think I lost the 3.3v on my project board in the first millisecond for this reason. After I soldered 18 resisters on my board so beautifully!
I will have better, more interesting, questions soon. I'm learning, ever so slowly.
Thanks for all your Insight, knowledge, Assistance it's invaluable.
Bill Cooley
Comments
E=I/R or E/R = I 3.3VDC/10,000 = 0.33ma So your Propeller pins are safe from excessive current. I am not sure the 100 ohm resistor does much of anything. The real question here is whether it is safe for 9 i/o pins to share one ground pull down. It seems safe to me.
But in some cases, pull up and pull down resistors can be too weak to do their job properly and you will see unreliable behaviour. No harm in testing to see what happens. But be fully aware that all 9 i/o pins should be set to input. If one of them accidentally is configured to output, you really need those 100 ohm resistors to protect i/o from damage and it might be wiser to go with 220 ohms.
I got those two values from an example on how to switch an LED through the Propeller.( you remember, at the very beginning) I thought the 10K was to make sure the pin saw 0/ground when not seeing 3.3v, rather than floating. You may have just said the same thing.
It was my assumption that may have been what took out my board, but now that you said things should be good, I have no idea why it doesn't 3.3v on the rail any more.
3.3 volts / 10,000 ohms = 0.00033 amps (0.3 mA)
Nine of those in parallel would be 2.7 mA, which should not be a problem.
The reference you give shows the 10,000 ohm resistors in a pull down arrangement. But the 3.3v is going into the Propeller via ONLY 100 ohms of current limiting
3.3v/100 = 33ma. Marginally high. I would be happier with 220 ohm resistors.
It could be that you got something backwards and have a direct ground from 3.3v to ground.
You have a 5VDC power source of 5 amps directly driving the 3.3VDC Propeller. If that is the reality, you have probably fried the Propeller.
The rest of the schematic looks pretty good.
If you powered up only one pair of Vdd and Vss on the Propeller, that would likely be another way you have damaged it. All the Vdd and Vss require being wired and capacitors need to be close to each pair.
I am relived to hear that. The square looked to much like a Propeller chip and I have to zoom and put on reading glasses to get all the details. I missed that label.
IF this was soldered up, there could be a nasty solder bridge just about anywhere pulling down the 3.3volt.
I have to check these with a 20x jeweller's loupe. .. I can't see them with a naked eye.