how small a box can i seal a bs2 into?

mobile_bob

i am working on embedding a bs2 into a small sealed box
i figure to have the pc board about the size of two 24 pin sockets, maybe a touch bigger.
there will be three stacked pc boards in the sealed unit, one for the processor, one for opto isolators
and one for a few led's to display out the front of the box.

my questions

1. are there any heat concerns, in other words, do i need to provide for aircooling for the bs2?

2. i want to bring all the pins out on a db25 connector (parallel socket), are there issues with interference that i need
to be concerned with?

thanks
bob g

Mike Green

It depends a lot on the power supply voltage. The higher the supply voltage, the more the Stamp's regulator has to dissipate as heat. Using LEDs and a lot of optoisolators will increase the current drawn (and may exceed the capability of the on-substrate regulator. If you haven't considered using an external 5V regulator mounted to the box as a heatsink, consider it. That's the greatest source of heat.

You're not doing any high speed switching so the socket shouldn't make any difference. If there's a static discharge to one of the connector pins, you might fry the Stamp (like picking up the box on a dry, cold day after shuffling across a carpet. It has happened. You just have to be careful about how and what you connect to the connector.

mobile_bob

Thanks Mike:

your point on the onboard regulator makes sense, i had thought of using a computer power supply for the 5 volt

power source. do you see a problem using one for this?

the static issue has me a bit concerned now that you mention it,

if i use a db25 female on the box so that the pins are protected from accidental contact would that eliminate much if not

all the concern?

what i want to do it build a unit that has one processor as a master, and then plug in a bank of slave processors (the little sealed boxes)

into it.

i do not see having to remove the slaves once the thing is up and operational, so my guess is static issues are not a concern

at that point.

so basically i need to get as close to 5 volts regulated in as possible, so the onboard regulator doesn't have to do much?

get it done and installed with minimal contact so as to limit the exposure to static issues?

thanks for your input

bob g

mobile_bob

Mike:

perhaps i should opto isolate all the I/O pins that are in use on the slave, and do what with the unused pins?

sink to ground via a resistor (pull down resistor?)

what do you think?

bob g

Mike Green

I wouldn't get obscessive about this. Consider that you'll have to observe the same precautions in handling your boxes as you would handling any Stamp or Stamp development board. There was someone who described some problems with a Stamp or Propeller logger for a race car with the system resetting at unexpected times when a programming cable was connected. An automobile is a very very noisy environment. There were suggestions like you mentioned ... using pull-down/up resistors, ferrite bead chokes, doubly shielded cables, etc. It doesn't sound like you'll have those kinds of problems.

My suggestion for an external regulator was to use a 5V regulator and not use the regulator built into the Stamp. You can supply regulated +5V to the Vdd pin and not use the Vin pin.