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PDB Question - external power — Parallax Forums

PDB Question - external power

GenesisGenesis Posts: 42
edited 2005-12-18 23:11 in BASIC Stamp
If I disconnect and leave OFF the power switch is it safe for the PDB to pipe regulated +5 into the VSS and VDD connectors on the PDB?

I need to measure actual current drain off a battery supply, and the only way to get an accurate number I can find is to go ahead and prototype up the voltage regulator and such that I intend to use, then feed it into the stamp.

With a regular breadboard I'd just put the stamp in and do it "the hard way", but since I have all the peripherals on the PDB, I'm wondering if I'm "safe" doing it this way?

I'm the L293 and the DS chips, so their contribution to system load isn't parasitic.· The only other item I can see that might be is the audio amp (which is not being used), but since its not being driven I wouldn't expect it to draw much.
·

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-12-18 20:03
    Anything connected to VSS and VDD would still be powering anything else on the board that ran from the regulated output.· The PDB is designed for development, but once you're ready, you should really build a prototype (Off the PDB) to effectively measure the current draw of your circuit.· Bear in mind that there are other properties that will change in a more permanent form of your project, for example, capacitance of the circuit/connections will be reduced once you're off the breadboard.· Your components may have different tolerances and such that could also affect the overall end readings.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • GenesisGenesis Posts: 42
    edited 2005-12-18 23:11
    Yep.

    Actually, a breadboard is pretty much worst-case in terms of noise coupling and such - any decent PCB layout should be better [noparse]:)[/noparse]

    I'm getting close to cutting a proto PCB for the project, as some of the things I really need to be able to do (specifically, shut off peripherals during "low current mode") are very, very hard to do on the breadboard due to component issues.

    I don't know what has gotten into folks, but finding a LDO +5V regulator with a shutdown terminal, for instance, is VERY hard unless you're willing to go with SMT parts. In theory ST has a very nice one (LF50CV5V) but trying to find that particular part is like pulling teeth. Its the package that's the problem - the same part in a surface-mount package is readily available, as is a TO220 - but the latter is MISSING the inhibit! ARGH!

    I know the world like SMT due to physical space issues but forcing prototyping onto a PCB in order to verify a design makes development costs go through the ceiling.....
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