How much power can the BS2 handle?

pcrobot · 2006-03-14 22:04

Hello,

I'm trying to run some stuff off the BS2 pins. How much power can 1 pin supply/handle at a time? I have functions that draw about 2.8mV, 2.2mV, and 25mV.

I don't want to hurt my Stamp, so I'm being cautious...

Thanks!

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Robotics
ro-bot-ics (noun)
the science or technology of robots, their design, manufacture, application, use, etc.

Post Edited (pcrobot) : 3/15/2006 12:03:34 AM GMT

Jon Williams · 2006-03-14 22:08

So cautious you didn't want to drop the manual on your foot so it was left on the shelf, right?·

Okay, all kidding aside, you can find the tech specs here: http://www.parallax.com/html_pages/tech/faqs/stamp_specs.asp

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Jon Williams
Applications Engineer, Parallax

pcrobot · 2006-03-14 22:26

Jon Williams (Parallax) said...
So cautious you didn't want to drop the manual on your foot so it was left on the shelf, right?

Okay, all kidding aside, you can find the tech specs here: http://www.parallax.com/html_pages/tech/faqs/stamp_specs.asp

Yeah, I looked at that EXACT page, and I must be missing something...

I have a BS2p24, BTW. Can one pin handle the voltages (one at a time) that I listed in my first post?

EDIT: OK, I may have figured it out.... I'm running these voltage across a 1 ohm resistor, so then 2.2mV is equal to 2.2mA, right?

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Robotics
ro-bot-ics (noun)
the science or technology of robots, their design, manufacture, application, use, etc.

Post Edited (pcrobot) : 3/15/2006 1:41:48 PM GMT

Jon Williams · 2006-03-14 23:26

When you refer to "functions," what exactly are you talking about?

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Jon Williams
Applications Engineer, Parallax

pcrobot · 2006-03-14 23:47

Jon Williams (Parallax) said...
When you refer to "functions," what exactly are you talking about?

Turning a fan, the blade (CCW & CW), and a power outlet on a hacked bread machine.

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Robotics
ro-bot-ics (noun)
the science or technology of robots, their design, manufacture, application, use, etc.

Post Edited (pcrobot) : 3/15/2006 1:41:15 PM GMT

Jon Williams · 2006-03-14 23:54

Do NOT connect them directly to the BASIC Stamp; use some sort of transistor buffer, especially for inductive devices like that.· This article should help: http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv6.pdf

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Jon Williams
Applications Engineer, Parallax

pcrobot · 2006-03-15 00:03

Jon Williams (Parallax) said...
Do NOT connect them directly to the BASIC Stamp; use some sort of transistor buffer, especially for inductive devices like that. This article should help: http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv6.pdf

My friend, who's using this to teach me, said to interface the largest mA/mV draw (the power outlet). But, He said to go ahead and hook-up the other functions. (2.2 to 2.8mA/mV) Keep in mind that I'm only going to be running them one at a time. (We're going to discuss the interface tomorrow) Is this OK?

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Robotics
ro-bot-ics (noun)
the science or technology of robots, their design, manufacture, application, use, etc.

Post Edited (pcrobot) : 3/15/2006 1:40:53 PM GMT

Jon Williams · 2006-03-15 00:13

You can do what you want to do... but is your friend going to replace your expensive Stamp when one of those devices damages it? Unless you get a signed statement saying as much, please take my advice and DO NOT connect any inductive device (motor, coil, etc.) directly to a BASIC Stamp or any other microcontroller.

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Jon Williams
Applications Engineer, Parallax

allanlane5 · 2006-03-15 00:33

It sounds like you're operating under a misunderstanding.

The BS2 puts out zero, and +5, volts on its I/O pins. Typically the symbol "mV" means milli-volts, or a thousandth of a volt. A milli-volt will do nothing to a fan. And a BS2 doesn't put out signals that small.

Now, the BS2 can put out about 50 mA (mA being milli-amps, or a thousandth of an amp.) at 5 volts. That's not going to do much to a fan either.

And a "function" is typically something you call in your source code. A "device" is something you hang off an I/O port.

I don't mean to be difficult, but with the terminology you're using it's difficult to determine what your problem is.

allanlane5 · 2006-03-15 00:37

Oh, and if you put a 1 ohm resistor between a BS2 I/O pin and ground, and then try to make the pin "HIGH", the following will happen:

V = IR. The BS2 puts out 5 volts. 5 = I * 1 ohm. 5 / 1 == 5, so you've created a situation where the BS2 could try to put out 5 amps. Now the BS2 will try to put out 5 amps, and its pins will burn out at around 50 mA, so damage to your BS2 is very likely in this instance.

pcrobot · 2006-03-15 12:49

OK, what I meant was devices... sorry for the misunderstanding.

I'm going to attach the instructions (scanned-in to a JPG file) I was given, as they can explain it all better than I can. I think I've been explaining things inaccurately.

Please look it over and list the potential problems.
Thanks for helping such a newbie...

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Robotics
ro-bot-ics (noun)
the science or technology of robots, their design, manufacture, application, use, etc.

Jon Williams · 2006-03-15 13:13

Without a schematic of the circuit or knowing what *was* driving those wires you are treading in very dangerous water. If you want to learn how to program a BASIC Stamp without doing damage, please consider our "What's A Microcontroller?" text -- you can download it as a PDF at no charge.

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Jon Williams
Applications Engineer, Parallax

allanlane5 · 2006-03-15 18:26

I think the idea of the lab is to connect a jumper wire between terminal 9 and terminal 5. This should turn on the motor going CW. You then measure the voltage between terminal 9 and terminal 10, which is actually across a 1 ohm resistor. V = IR, so your measured voltage (in millivolts) divided by 1 (the value of the resistor) will give you a value in milliamps.

That value, in milli-amps, is what it takes to activate the motor going CW.

Repeat the above process after moving your jumper so it is now between terminal 9 and terminal 6, which runs the motor CCW. In fact, you should repeat the process for each "input" pin on the bread machine (which are pins 5,6,7 and 8). The result should be a table with 4 entries -- for each pin, what is the current needed at that pin to turn on that function (function OF THE BREAD MACHINE, that is).

If any of those values are above 2 mA (and I bet most of them are) then you can come back here and find some interface circuits for driving the resulting currents.

P.S.· Aha!· Now I see what "I'm trying to run some stuff off the BS2 pins. How much power can 1 pin supply/handle at a time? I have functions that draw about 2.8mV, 2.2mV, and 25mV." means.

So, 2.8 mV corresponds to 2.8 mA (because of the 1 ohm resistor, right?) 2.2 mV becomes 2.2 mA, and 25 mV becomes 25 mA.

So you need a driver circuit for the 25 mA pin.· A Darlington Array chip would work well at these currents.

pcrobot · 2006-03-15 18:44

allanlane5 said...
I think the idea of the lab is to connect a jumper wire between terminal 9 and terminal 5. This should turn on the motor going CW. You then measure the voltage between terminal 9 and terminal 10, which is actually across a 1 ohm resistor. V = IR, so your measured voltage (in millivolts) divided by 1 (the value of the resistor) will give you a value in milliamps.

That value, in milli-amps, is what it takes to activate the motor going CW.

Repeat the above process after moving your jumper so it is now between terminal 9 and terminal 6, which runs the motor CCW. In fact, you should repeat the process for each "input" pin on the bread machine (which are pins 5,6,7 and 8). The result should be a table with 4 entries -- for each pin, what is the current needed at that pin to turn on that function (function OF THE BREAD MACHINE, that is).

If any of those values are above 2 mA (and I bet most of them are) then you can come back here and find some interface circuits for driving the resulting currents.

P.S. Aha! Now I see what "I'm trying to run some stuff off the BS2 pins. How much power can 1 pin supply/handle at a time? I have functions that draw about 2.8mV, 2.2mV, and 25mV." means.

So, 2.8 mV corresponds to 2.8 mA (because of the 1 ohm resistor, right?) 2.2 mV becomes 2.2 mA, and 25 mV becomes 25 mA.

So you need a driver circuit for the 25 mA pin. A Darlington Array chip would work well at these currents.

I knew that the instructions would help you understand better than I could. So, I need an interface curcuit for all of them? Or just the 25mA one?

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Robotics
ro-bot-ics (noun)
the science or technology of robots, their design, manufacture, application, use, etc.

allanlane5 · 2006-03-15 19:26

Just the 25 mA one. The BS2 can drive 3 mA outputs just fine.

That's assuming your figures are correct. Even if you're incorrect, if you put a 220 ohm resistor in series with the BS2 I/O pin, your chip would be protected.

pcrobot · 2006-03-15 20:16

allanlane5 said...
Just the 25 mA one. The BS2 can drive 3 mA outputs just fine.

That's assuming your figures are correct. Even if you're incorrect, if you put a 220 ohm resistor in series with the BS2 I/O pin, your chip would be protected.

Well, I just got the fan, and the bi-directional blade working! Now for the outlet!

Thanks for all your help, BTW!

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Robotics
ro-bot-ics (noun)
the science or technology of robots, their design, manufacture, application, use, etc.

How much power can the BS2 handle?

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