Quick question... BOE + BS2 + BS2OEM

Ugha

I'm pretty sure of this (I did the math for once) but I want to just double
check before I try it...

Can the BOE power both a normal BS2 and a BS2OEM(powered from VDD)
using 4AAs?

Mike Green

Post your math and ask for confirmation.
I can give you an answer by doing the math myself, but you won't learn much from that.

Ugha

Sorry for the delay on responding...

I suddenly realized that the BS2 OEM may have different power requirements than a normal BS2... but so far I've
found no information one way or another... other than the BS2OEM possibly having better power regulation.

My math before was simple... a LM294oct-5 voltage regulator can put out around 1A... and a BS2 only consumes 7mA
during normal operation... which means a single BOE could supply power for several BS2s.

This, of course, isn't including the other components in the circuit... but that strays from the purpose of the post.

Am I right?

Does anyone know the differences between a normal BS2 and a BS2OEM?

Mike Green

Ya gotta do the work. It's not hard. You make two lists, one for the BS2 (based on the schematic) and one for the BS2OEM (based on the schematic). The processor is the same and the EEPROM is the same. You look at the amount of current used by the regulator itself and the programming circuitry. They use different regulators and there are some 4.7K resistors part of one and 10K resistors in part of the other. I'm sure the differences are small.

Ugha

Ah... that sounds like it'd be a good learning experience [noparse]:)[/noparse] I'll try to do that sometime in the following week.

Is my basic concept of running two BS2s off a single BOE alright though? Am I correct in that?

One other question... since each pin can handle a decent amount of current... can a BS2OEM be powered straight
from an I/O pin of another stamp?

Or would using a relay be better? And can you explain why?

Sorry for bugging you Mike, but you know me... unending thirst to learn all things Stamp.

Mike Green

Sure, you can run several BS2OEMs (and the mounted BS2 module) from the BOE regulator's output. You just have to watch the total current drain and the heat load on the regulator. Don't use too high of a Vin and that'll keep down the regulator's power dissipation. 6V is enough. 7.5V is plenty. Avoid 9V or higher.

Again, you need to figure out the total current load. This includes I/O drains. If you light an LED on a BS2OEM I/O pin, that's at least several mA depending on the current limiting resistor and the LED. You can use a relay to switch power for a BS2OEM. The advantage is that there's practically no voltage drop across the relay contacts. If you use a switching transistor, you may lose 0.3V. RadioShack has some nice 5V coil reed relays that can be driven directly from a Stamp I/O pin. They draw 24mA. Be sure to connect a reversed diode across the relay coil. You can't use more than two of these on a Stamp. Use a switching transistor on each if you need more.

A better solution might be to use a voltage regulator for the BS2OEMs that includes a shutdown pin and drive that from a Stamp I/O pin. It's a logic level input.