Subject:
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Re: Sonar Transducer Multiplexor
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sat, 29 Mar 1997 09:35:52 GMT
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Original-From:
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Adam <adam@ring.zenox.SPAMLESScom>
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Viewed:
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1492 times
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On Fri, 28 Mar 1997, MAR ERICSON wrote:
> In your BMP circuit diagram that you posted recently, why did you use an
> open collector to feed the base of the transistor?
The OC is simply a protective buffer to the SPI pins. When the SPI
feeds a low with a pullup resistor it must be able to sink the current
drawn by the resistor. I read some of the docs on the SPI pinouts and
("M68HC11 Reference Manual" Serial Port D Pins - pg 2-19) there is mention
that pullups are required. Anyhow it may be overprotective. BUT, better
safe than sorry. Oh yeah, another reason was because I wasn't quite sure
when I drew it up for the 1st time whether or not the 5V supply would be
sufficient to driving the MOSFET to saturation. I was thinking I might
need external power to the pullup higher than 5V - which I definately didn't
want going through the 6811.
> Would it work if you connected the digital signal directly to the base?
I wasn't sure the signal would be powerful enough to saturate the MOSFETs.
In reading the application notes that International Rectifier supplies
in their data books, I discovered their suggestion to using the OC with pull-
ups when driving the MOSFETs via a TTL signal. When in doubt read the appli-
cation notes. They pay those engineers some serious cash for those notes.
>
> -----------
> ericson mar
> Master of Engineering Candidate
> Project: Mobile Robotics
> mar@cooper.edu
> (212)353-4356
>
> Department of Mechanical Engineering
> The Cooper Union for the Advancement of Science and Art
> -------------------------------------------------------
>
>
----------------------------------------------------------
Adam B. Cox check out my web page
Computer Engineer http://www.zenox.com/~adam
Zenox Communications Corp. vmail: 416-241-7000 (x224)
----------------------------------------------------------
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Message is in Reply To:
 | | Sonar Transducer Multiplexor
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| In your BMP circuit diagram that you posted recently, why did you use an open collector to feed the base of the transistor? Would it work if you connected the digital signal directly to the base? ---...--- ericson mar Master of Engineering Candidate (...) (27 years ago, 29-Mar-97, to lugnet.robotics.handyboard)
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