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John Kauffman
09-21-2008, 11:22 PM
The search strings I’ve used for the P’lax site have not brought usable results for following question.

To date I have only used STAMPS on the Board of Education or Homework board.
I’m now building a project that has to be as small as possible. I’d like to put a BS2p24 in a DIP socket and solder it and the other components on a very small pcb protoboard.

The programming connection (pins 1-4) looks pretty easy based on schematic for BOE.
But I am unsure of the power supply. Power is from a 9 volt battery.

What is the minimum circuit I need to power the STAMP?

Do I have to use the LM2940 & 1000 uF cap or can I directly wire 9v battery red to Vin and Black to Vss?

If I don’t need the reset feature, should I solder a bridge from pin 22 to Vdd (pin 21)?

Thanks.

PJ Allen
09-22-2008, 12:22 AM
The BS2p24 has its own on-board regulator. Any external device would be for powering peripheral devices.

http://www.parallax.com/Portals/0/Downloads/docs/prod/schem/BS2p24SchematicRevD.pdf

Amaral
09-22-2008, 03:56 AM
you can connect direct the 9V batt to Vin pin !

You don't need to pull up the reset button ! it will be pulled up internally !

hope to help

Amaral

John Kauffman
09-22-2008, 12:52 PM
I'd like to power a Memsic 2125 in the project. The datasheet says the Memsic can take up to 5.25 volts and draw up to 5 mA.

It looks like there are three options to power it:
1 - Add a voltage regulator to the project
2 - Power 2125 from BS2p pins 21 (Vdd) and 4 (gnd) since the pin 21 is after the on-board volt reg and thus at 5v
3 - Power 2125 from an I'O pin set high (should be under the 25 mA rating of an IO pin) and pin 4(gnd)

I'd prefer not to add the volt regulator. Any opinions on other two options?

Mike Green
09-22-2008, 01:50 PM
Both #2 and #3 have been used before for loads within the limits of the source involved.

With #2, remember that other circuitry on the module draws some current (including the SX)

With #3, remember that 25mA is a bit generous and there are limits for groups of 8 pins.
5mA is not much. Also, the Voh is less than 5V. Check the output graphs for the SX to see
what the actual voltage will be at 5mA. It's probably ok for this application, but don't just
take my word for it.