Strange phenomenon from BASIC Stamp
Hyblademin
Posts: 4
I first noticed this while testing a program on my BASIC Stamp: When I come into contact with the BASIC Stamp itself, strange things seem to be liable to happen.
When I touch the continuous rotation servos' respective I/O pins on the stamp, they begin to rotate at full clockwise. I thought I was crazy when I couldn't replicate the phenomenon, but then I realized it only happens when I'm not grounded against the metal chassis. I've also discovered after some tinkering that this effect is only present when the USB cable is connected to my laptop (the mini-B end that plugs into Boe-Bot only need be touching any metal part of the assembly). Naturally, grounding myself to the USB cable itself also hinders the motion. However, while a program is running, it is still possible to observe rotation even if the USB cable is not connected. Since the servos are driven by PWM, why is this happening? I'm stumped.
This seems to occur whether I am physically grounded to the earth or not, though I haven't tested this extensively.
When I touch the continuous rotation servos' respective I/O pins on the stamp, they begin to rotate at full clockwise. I thought I was crazy when I couldn't replicate the phenomenon, but then I realized it only happens when I'm not grounded against the metal chassis. I've also discovered after some tinkering that this effect is only present when the USB cable is connected to my laptop (the mini-B end that plugs into Boe-Bot only need be touching any metal part of the assembly). Naturally, grounding myself to the USB cable itself also hinders the motion. However, while a program is running, it is still possible to observe rotation even if the USB cable is not connected. Since the servos are driven by PWM, why is this happening? I'm stumped.
This seems to occur whether I am physically grounded to the earth or not, though I haven't tested this extensively.
Comments
A couple of simple solutions -- 1.· Don't do this.· 2.· Add a 10 Kohm resistor between the I/O pin and ground -- this will give you a local 'zero' signal your finger wouldn't be able to overcome.
seriously though it's true, you'll be surprised what you see on an oscilliscope when you touch the end of the probe.
·You didn't post a schematic of your hardware, So I can't tell you for certain Whats wrong.
I think you have some inputs on the Stamp that are floating and need to be pulled high or low with a resistor, 10kohm is the common value for this PullUp or PullDown resistor.
·I have added a little drawing for PullUp and Pulldown resistors
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