Buy 'em and fry 'em
jhoyoza
Posts: 72
Hi again all,
As a hobbyist certainly, I know enough to be dangerous! Frying equipment is becoming a specialty of mine! Just kidding, actually I’m doing quite well.
This forum has certainly been very helpful to me in the past and now it’s time for the next (Dumb) question.
In one sub-system, the power source are a pair of 9.6V High- Energy (typical) hobby type rechargeable NiCad’s. I would like to send a signal to the basic-stamp in order to tell the program the particular sub-system has been activated, and to adjust accordingly. Following conventional rules I would only require a 220 ohm resistor to reduce current draw to less than 20ma (After making 5VDC using a couple resistors) when using one of the BS2 pins as an input and 9.6VDC as a primary source?
I simply want to avoid frying another BS2 if I can! (Fingers crossed.. knocking head on wood…etc.) In another non-related instance I was told RF/EMF noise was the cause of one of my chip-failures, and to include a zenier-diode to stabilize the motor voltage.
Should I also use a 100K pull-up or a pull-down resistor with it in my newest venture? Or perhaps another diode, or a capacitor? And despite grounds being common, a very powerful (for a BS2 input anyway) separate power source is also driving a DC brush-Motor? ( I get ~3 OHMs across the motor windings) Perhaps I may be setting myself up for more noise and/or voltage instability issues?
Thank you,
-J the deadly one
Post Edited (jhoyoza) : 10/29/2006 5:02:04 PM GMT
As a hobbyist certainly, I know enough to be dangerous! Frying equipment is becoming a specialty of mine! Just kidding, actually I’m doing quite well.
This forum has certainly been very helpful to me in the past and now it’s time for the next (Dumb) question.
In one sub-system, the power source are a pair of 9.6V High- Energy (typical) hobby type rechargeable NiCad’s. I would like to send a signal to the basic-stamp in order to tell the program the particular sub-system has been activated, and to adjust accordingly. Following conventional rules I would only require a 220 ohm resistor to reduce current draw to less than 20ma (After making 5VDC using a couple resistors) when using one of the BS2 pins as an input and 9.6VDC as a primary source?
I simply want to avoid frying another BS2 if I can! (Fingers crossed.. knocking head on wood…etc.) In another non-related instance I was told RF/EMF noise was the cause of one of my chip-failures, and to include a zenier-diode to stabilize the motor voltage.
Should I also use a 100K pull-up or a pull-down resistor with it in my newest venture? Or perhaps another diode, or a capacitor? And despite grounds being common, a very powerful (for a BS2 input anyway) separate power source is also driving a DC brush-Motor? ( I get ~3 OHMs across the motor windings) Perhaps I may be setting myself up for more noise and/or voltage instability issues?
Thank you,
-J the deadly one
Post Edited (jhoyoza) : 10/29/2006 5:02:04 PM GMT
Comments
A Zener diode may not be the best solution for motor noise. Better is specific noise filtering with at least a 0.1uF capacitor across the motor windings and at the power source. Make sure your wiring is heavy enough, particularly the ground wiring. Look up "ground loops" on the internet and search these forums for it. You might look it up in the Wikipedia as well. Anytime you have relatively high power devices (like motors) mixed in with logic (like the Stamp), you have to be careful to isolate the noise (including ground noise induced in the ground wiring) as best as possible.
About your current venture. The resister between the Stamp pin and ground will act as a pulldown when the subsystem supply is off. The subsystem itself should have filter capacitors, so you probably don't need more.
About wiring ... You don't want to run logic signals and power for logic circuits in the same bundles as power for motors and other noise sources. Some of the noise will couple into the logic wiring. If you're going to do this anyway because there's no effective choice, use twisted pairs as much as possible for both. You can use several twisted pairs in parallel for high power loads with one (+) wire twisted with each (-) wire.
“A ground loop is an unwanted current loop. The current flowing in the loop generates additional noise and provides no benefit to the circuits operation.”
Or how about this:
“Isolation, The practice of grounding remote sensors is usually advised to reduce noise pickup and protect equipment from being damaged by lightning or other high voltages. If both sensor and signal conditioner are grounded, it is possible to get an unwanted current, due to ground-to-ground potential differences, known as a ground loop. Ground loops degrade signal quality to the point of uselessness and can harm receiving equipment and personnel. “
Or even:
“The control signal must be electrically isolated from the motor power. This means that a multi-meter connected between the motor power ground and the instrumentation ground (control signal ground) will indicate open (infinite resistance).”
And perhaps closer to my taxonomy:
“Back EMF – back EMF (electromotive force) is the very short duration voltage spike produced by an inductor when the applied voltage is instantly removed. All DC brushless motors generate back EMF and the magnitude of the back EMF can easily exceed the steady state voltage supplied to the motor. Unless filtered, back EMF can cause electrical noise that can reduce performance levels and reduce reliability.”
I stole every word of it!
So if I just keep grounds separate I will no longer have noise? Hmmm….However, I did, even if just for just for a moment, consider isolating every system in a steel metal boxes connected by heavy wire, heavy contacts and double insulate everything? But my plastic model-boat would sink for sure! However, knowing with confidence…while holding my hat over my heart…that not even one single little fishy would be electrocuted!
I most certainly, and absolutely appreciate the detailed component info, and find the filter capacitor information most valuable when pointing toward controlling a DC motor’s potential to create ‘noise‘, and apparently lightning. However, I’m very curious about how one might calculate the actual value of such capacitance? Rule of thumb? Experience? Einstein Math?
Respectfully yours,
-J
Post Edited (jhoyoza) : 10/31/2006 10:40:30 PM GMT
1uF or 10uF will be find for power supply noise (usually caused by inadequate filtering in the first place).
0.1uF for higher frequency noise....
Then there's the type of capacitor...mylar/electrolytic. It is a can of worms for sure.
I'll typically stick to 1uF/10uF or 0.1uF's and just pick the appropriate voltage rating for my application.
Not really an answer...but what's the use and what's the noise?
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Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."