best general I/O pin protection ?
FlyingFishFinger
Posts: 461
Hi all...
What is the best idea to protect my stamp pins from "uneducated" PCB handlers ?
I mean, do I put something between my pins and my terminal block (resistors? What value?)?
I'd like a minimum of interference with stamp functions.
Rafael
What is the best idea to protect my stamp pins from "uneducated" PCB handlers ?
I mean, do I put something between my pins and my terminal block (resistors? What value?)?
I'd like a minimum of interference with stamp functions.
Rafael
Comments
Rafael
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Chris Savage
Parallax Tech Support
csavage@parallax.com
No, I'm just making my own personal general purpose controller board. I don't think I can market stuff at my age (15) except maybe on eBay...hahaha
Rafael
If you don't need that much, the 74HC07 chip can work on both the input and output. If you really make a big boo-boo, that is the chip that will smoke.
The 220 resistors assume that you are limiting current and that the voltage will always be within reason. If you are the kind of person that gets the 12volts or 24volts confused with the 5volts; or get your DC mixed with your AC - use the 74HC07 as a cheap sacrafice to the gods of misfortune.
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
So if I use the 74HC07, do I still neeed the resistors? The hex buffers just go in line with the I/O without any further ado?
Thanks
Rafael
The big advantage with resistors is that· both the in or out direction are allowed and·okay.··But, one problem is that you may need more resistance to protect LEDS [noparse][[/noparse]I use at least 330 ohms and often 470 ohms as I seem to burn up LEDs].
You certainly don't need the resistors between the Stamp and the buffers, but with the hex buffers, you have·two design dilemmas.· [noparse][[/noparse]That is why I suggested the 'HC' in 74HC07].
Dilemmas
1. How do you know what you want to input and what you want to·output?· The 74HC07 only works in one directiong. ·Parallel inputs and outputs of 8 bits·for bytes are best grouped consecutively. But if your I/O is in bits only it doesn't matter much.·
2. 16 I/O lines divide by six either leaves four lines unprotected or two extra hex buffers. Either you choose 2 DIPs and come up short or 3 chips and have left over buffers.
Don't forget to provide +5volts to the chips too.· Resistors don't need a power supply. You may want to use RC circuits to create timing.· While I think it will work well with most everything, I am not absolutely sure that the buffer will not interfer with such designs.· Some Trial and error is involve here.
Mostly, I think the buffers are great for tinkerers that do things they·feel they·shouldn't [noparse][[/noparse]like hot swap wiring rather than turn off the circuit].·
You might just want to have this built as a temporary breadboard set up until you get futher along.· The best protection is to really develop you·technical skills.· While I had the knowledge, I was very rusty in the beginning with my skills and made a lot of stupid blunders which made me fear I did some damage. Luck was with me though.· The BasicStamp is a very tough little device compared to most microcontrollers.
After you get better at understanding your own bad habits, they will disappear.· Then you don't need all that protection unless you are trying something that you are unsure of [noparse][[/noparse]like driving an unknown motor directly from a Stamp].
If you really have doubts about trying something, you can always ask here for help.· If you establish a reliable information source, you can send a Private Message directly to that person.· Most of us enjoy sharing knowledge and I certainly learn much by sharing information.
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Post Edited (Kramer) : 11/20/2005 6:15:35 PM GMT
I'm worried about protecting my auxio. I'm probably the only person who's going to use the board, but sometimes I get absent-minded and otherwise you can never know.
Rafael
I use 4N39's (I think that's what they are...they're not here)....and it does require a bit more overhead, but if you are running things outside to sensors, then I'd use these (again depending on your measuring scheme) as the opto will hopefully pop if a surge makes its way on to your lines.
Further to this....general safety handling is required!
Don't drag your feet on teh ground then expect to fondle your stamp (I only do that on saturday nights when I'm alone! [noparse];)[/noparse] JOKING!).
Also, any wires you do run should not be run WITH AC voltage lines. If they have to go near AC lines, then try to run that perpendicular to the each other, as this will reduce the amount of noise your lines pick up.
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·
Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
Thank you all
Rafael