Can U Explain This BS1 Phenomenon?

Humanoido

I like to experiment with Stamps and build Stamp projects. Last night while working on a new project with a BS1 Project Board, the 9-volt battery went down to almost nothing, however the Stamp continued to work
and function properly. I first noticed the battery condition by the dim power LED. The battery was reading 1.2 volts under load.

At that time, I went over to the new SEED Stamp Supercomputer and attached a Bench Power Supply with adjustable voltage. All ten processors were powered up. Starting from 9-volts, power was backed off gradually. A program was running which kept all ten piezo speakers making lots of noise. Each power LED was lit, and the stamp collective continued to perform well down to 2.2 volts. The amps draw was at elevated to 181 ma.



As the volts were backed off to 2.1, one of the boards fell off and its power LED extinguished. At 2.0, then 1.8, two more boards fell out of the collective. The experiment was repeated and this time the processors fell out at 2.0 volts. Can anyone explain Stamps working on 2 volts? I think I will build more projects from this low power Stamp board.

humanoido
Stamp SEED Supercomputer

Post Edited (humanoido) : 6/26/2009 6:58:27 AM GMT

Leon

Many years ago the Z8 was one of the first CMOS MCUs, intended for 5V operation. I experimented with low-voltage operation and had one working at maximum speed with a 1V supply. The whole board was CMOS, of course, including the address latch and the EPROM.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Post Edited (Leon) : 6/26/2009 10:12:57 AM GMT

Humanoido

It looks like we don't need the full 9V of a 9-volt battery, though their small size may be the convenient aspect.

humanoido

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Stamp SEED Supercomputer

Humanoido

@ Leon

You could have used a 1.5V AA battery!

humanoido

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Stamp SEED Supercomputer

Mike Green

The voltage regulator used in the BS1 (see the schematic for the BS1 - www.parallax.com/Portals/0/Downloads/docs/prod/schem/BS1SchematicRevB.pdf) has a 0.2V drop out voltage, so it should regulate down to a 5.2V input voltage. What I don't understand is that the BS1 includes a voltage detector set at 4.3V that provides a reset to the processor when the Vdd supply drops below 4.3V and, for the board to run at 2V, that must have failed. The voltage detector is there because the processor (PIC16C56) is supposed to have its own voltage detector to shut the processor down (in reset) when there's not enough voltage to run it reliably, but Parallax found that it was set too low and it started making mistakes before it would halt ... not good, so they added an external "brown-out detector".

The current PIC16C56 is rated to work down to 2.0V. Maybe Parallax left out the "brown-out" detector on the HomeWork Board. I can't find a schematic for it and I don't have one to look at.

Humanoido

@ Mike
I understand it now. I have the revision B Stamp 1 Project Board and
the latest schematic for revision C. Both schematics (rev b and rev c)
show the brownout detector.


Excerpt from the Stamp 1 Homework Board
Schematic Rev. C showing a brownout detector
on pin 4

However, as you can see in my microscope's photo, every reset pin on
every project board that I have (Rev has no brownout detector,
and no connection to pin 4 (res).


Microscope photo showing the BS1 chip with no connection on pin 4.

If you ask me, leaving off the brownout detector on the BS1 is a huge
advantage and a good judgment call by Parallax Engineers. It's likely that
circuits with 9V batteries will last far longer without it, because of the
chips rating down to a mere 2 volts.

It also opens up new possibilities for running some circuits (the piezo
speaker in this example) with a couple tiny AAA batteries. It is also
likely two watch cell batteries could power the stamp without any
5V sensor requirements.

humanoido

Post Edited (humanoido) : 6/26/2009 5:16:27 PM GMT

Mike Green

I assume that Microchip fixed the issues with the built-in brown-out detector in the PIC16C56, so Parallax was able to leave out the extra parts. Thanks for the picture.

Leon

humanoido said...
@ Leon

You could have used a 1.5V AA battery!

humanoido

I actually used a discharged 1.5V cell giving about 1V, as I didn't have a suitable PS!

Leon

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle