WAM V2.2 and the Homework board -- the 220 ohm resistors

LoopyByteloose

I see that the Basic Stamp Homework board supposedly has 220 resistors 'protecting' all the I/O.

If I were to follow the WAM text and use a 470ohm resistor in line with an LED plus another 220 ohms, I suspect that it would barely light.

No mention in the WAM text of altering values for the different board. But this is certainly a persistent consideration throughout the text. Anyone teaching this will have to alter every activity that involves an I/O line to compensate for the 220 ohms.

I am not sure of all the implications, but it makes me kind of grumpy. The first thing a kid is going to ask when I use a provided 220 ohms in series instead is "Where are the 250ohm resistors? Isn't that one going to do something bad?"

I guess I will just have to rise to the occasion and explain that the LEDs just burn a little brighter at 440 ohms, and even brighter at 330 ohms, and brighter yet at 270 ohms. But if you go much further, they burn up - like this.......

LoopyByteloose

Another discovery about the Homework Board. It only provides 50ma of +5VDC.

The WAM kit that came with it includes a servo for the course work, so this is a significant issue. When the teacher gets to the work with the servo, additional power is going to have to come from somewhere else. Motors are very power hungry, so it looks like a 4x AA battery pack is going to have to provide about 6 volts to the servo, share ground with the Homework board, and connect to an I/O for PWM control.

Not too bad, once one thinks about it.

I really like the simplicity of the Homework Board, but am a little shocked that it has such a small voltage regulator that looks so big.

Nonetheless, this is the PIC16C57 version of the BasicStamp2 that runs on the least power of all of them and can be put to sleep for long periods with the 9 volt battery plugging away at micro amps of current. It is a very nice self-contained little unit that a kid might wait for days for it to wake up and do something wonderful.

GordonMcComb

The regulator on the HomeWork board delivers *500* mA, not 50. In sleep mode the chip pulls 50 uA.

While the 220+470 ohm series resistance will make the LEDs glow a little less, they're still quite visible. The fact that LEDs grow brighter with lower resistance/more current is part of the learning experience. Seems to me you'd want to demonstrate this, as it's a core principle of electronics.

Except for the Altimeter, where the code is too demanding for the Stamp, there are working examples using the HomeWork board for all the KickStart how-tos on the Learn.Parallax site. This includes a demo of a servo. With a fresh 9V battery you can operate it for several minutes no load, definitely enough for demonstration.

-- Gordon

LoopyByteloose

@GordonMcComb
Something is wrong with the documentation for the Homework board (I hate typos, even my own). I was a bit gobsmacked by a mere 50ma and am a lot happier with 500ma. I was originally trying to verify the 220 ohm resistors when I came across that.

And it seemed all wrong as I have a tiny 100ma +5V 7805 sitting on my desk for a future project. I thought that is a HUGE 50ma regulator!!!!

In the past, I have had difficulty lighting a LED at 470 ohms, but it was pulsed. Nothing really wrong with having the 220 ohm protection resistors in place. But I just wanted to provide a 'heads up' for WAM teachers and students that they should be included in the math.

Regarding the r/c servo, it really would be best to just have a different battery pack if any load is applied. The battery pack wouldn't have to be regulated as long as the voltage is not out of the proper range. R/C servos were long used in that fashion on model airplanes and boats. But it does seem the new ones are expecting the ESC to provide a regulated voltage to them.

I wonder what the quiescent current of the voltage regulator is at 9VDC when the BASIC Stamp is in sleep mode. My guess is a switcher would be more idea for having it stand-by for long periods. One just has to DIY if they want everything.

I've been working thorugh the WAM manual in both English and Chinese and will start teaching to my first student on a one-on-one basis next week. He is very excited as he liked the LEGO Mindstorms class that he took, but he felt it was too short and too simple.

LoopyByteloose

Up until now, this has been a paper chase. I have been trying to read all the teaching material and catch all the details that I need to run down. That has pretty much settled down.

But there is one last item of great importance - try all the tasks that I am going to teach for a session before I meet the students.

I am very curious to see if the 470 ohm resistor in series with 220 ohms on board will light all the various LEDs. 690 ohms seems quite a bit. But we will see. 5 volts / 690 ohms = 7.25ma

I may not get into Chapter at all, but I should be prepared to do so if Chapter One moves ahead very quickly.

Mike Green

An early version of the Homework board did have a 50mA limit on the +5V regulated supply.

LoopyByteloose

Hi Mike! Yes indeed.
I now see that I downloaded documentation via a Google search from a vendor that didn't provide the newer information.

Today, I started working thorough the actual activities and immediately attempted to insert the 9 volt battery backwards. So I went back to the documents to see if reversed polarity was protected by the regulator (it is).

The current specs are for an LM2936 (500ma), but I see I have the more powerful LM2940 (1000 ma - an undocumented upgrade).

I also had to sort out the green on-board LED only lights when a program is running. It no longer wastes electricity by being on when the microcontroller isn't active. The LED behaving unlike a pilot light is what raised my initial fears that I'd damaged something.

But the fact is NO damage and the set up is nearly impossible to damage. And the bottom line is that the teacher has to study everything to stay ahead of the student.

It is a great little board, just a bit different from what I am used to. It will take a lot of abuse from kids.

LoopyByteloose

Moving on from hardware and back into the teaching material.

The Basic2 has 42 commands that I feel I should be able to present in a comprehensive fashion, but one Taiwanese teacher friend took a quick look at the material and quickly threw it back at me with the the comment "Way too busy!"

I respect her opinion as she is one of the hardest working and most successful native Taiwanese English teachers.

So it looks like I may just excerpt the 42 commands from the larger BasicStamp Manual. The children that I have shown the original text dislike it very much. They really don't know what to do with it.

It may be worthwhile to have a Kid's version for other teachers. I learned Fortan when you were just given a text with commands, not a whole list of directives and conditional compilations and so on. This is all about keeping the material simple enough to make the student feel comfortable with it, not overwhelmed.

Still there will always be a need for a comprehensive document for fully competent users.

It would also be much easier to get the 'abridged version' translated into Chinese. And that would be sublime.

LoopyByteloose

First class was taught today. We covered all the material in Chapter 1, but skipped the stuff before Activity 4 as the software was already installed and verified on my notebook.

The boy was hoping that I would bring him a complete robot, rather than just a 'CPU' as he claimed it to be. But I explained that while the Lego Mindstorm system had all that, he was going to learn more this way. I promised to give him my Toddler if he finished the WAM book. Since there is a photo of it in the back of the WAM text, he seemed fine with that.

Had to explain the limits of the math to 16bits (65,535) and that even two numbers that are multiplied and exceed that will produce garbage.

Also, created some Do..Loops with DEBUG so show that there are perpetual loops as well as just running through a list and ending.

And showed PAUSE as a means to get the loops slow enough to be able to read the Debug text.

So now I have to prepare for Chapter Two (which he has the Chinese version to preview) and get some idea of what to additionally teach (Like Toggle, High, Low, Pin numbering, Looping for a limited number of times, embedded Do..Loops.