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'[PIC]Voltage pull-ups for 1.5v signals? was Newbie'
2004\10\06@070539 by Mcgee, Mark

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I have a couple of not-strictly PIC questions surrounding my PIC based
fermentation temperature controller.

The FE33L temperature control unit that I am intending to use runs on a 1.5v
supply, and hence, the clk, data, and 2 other control pins operate 1.5 v for
high, and 0v for low signals.

Is there a simple way (i.e. in an IC) to amplify these (non inverted) to 5v
for the PIC to read?  I know I can use a transistor for each line, and invert,
but I'd rather not invert the signals if I can help it.

I did see a SN54HCT573 bus/latch, but I don't think that'll 'amplify' as such.
Actually, I'm not sure what the SN54HCT573 is useful for...

Regards,
Mark

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2004\10\06@080019 by Alan B. Pearce

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>I did see a SN54HCT573 bus/latch, but I don't think
>that'll 'amplify' as such. Actually, I'm not sure
>what the SN54HCT573 is useful for...

It will not level shift the signal in the manner you need. Look here for
some examples.
para.maxim-ic.com/compare.asp?Fam=bidirtranslators&Tree=Interface&HP=Interface.cfm&ln=
and part way down is MAX3001 which looks like it may do exactly what you
need. You may also be able to get these as samples, and hence for free, by
filling in an application on the web site.

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2004\10\06@081638 by Russell McMahon

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> The FE33L temperature control unit that I am intending to use runs on a
> 1.5v
> supply, and hence, the clk, data, and 2 other control pins operate 1.5 v
> for
> high, and 0v for low signals.
>
> Is there a simple way (i.e. in an IC) to amplify these (non inverted) to
> 5v
> for the PIC to read?  I know I can use a transistor for each line, and
> invert,
> but I'd rather not invert the signals if I can help it.

I'd actually invert the signal as it takes less hardware and is still
trivially easy to deal with in software.

However -

I assume that the FE33L output is NOT open collector ie it is driven both
high and low actively. If it is open collector then it will need a pullup
resistor of about 1M from transistor base to transistor emitter in each
channel below.

Make a resistive divider from 5 volts to ground so there is about 1.5v at
the midpoint
(Needs not be overly accurate. Slightly low better than slightly high).
eg 5v - 6k8 - point X - 2k2 - ground gives 1.2V at point X.
100 uF capacitor from point X to ground.

Point X may be shared between multiple transistor switches below.

Per channel:
NPN transistor
100k resistor, collector to 5v
Base to point X above via a 100k resistor.
Emitter to output of FE33L
Collector to PIC pin.

You can build a divider for each channel if you wish - in which case you
connect the base directly to it's own divider and don't need the 100 uF cap
or the 100k resistor to point X.



Operation:

FE33L output low
Emitter low
Transistor on
Collector low.
PIC pin low

FE33L output high
Transistor off
Collector pulled high by 100k collector resistor
PIC pin high



       Russell McMahon

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2004\10\06@100729 by Mcgee, Mark

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That looks perfect, but do you think I can find a MAX3001E on Maplin or RS?
Nope.

Any recommendations for UK eletronics (internet)mail order companies?  This is
hobby stuff for me though, not commercial.

Regards,
Mark

> {Original Message removed}

2004\10\06@104029 by Dave Lag

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Just a dangerous thought- could you bias the ground of the sensor a diode
drop above
your real ground?
'Guess you would would need to research if  -0.7v (low) will harm anything
downstream.
Experts?
D

At 07:05 AM 10/6/04, you wrote:
{Quote hidden}

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2004\10\06@110740 by Alan B. Pearce

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>That looks perfect, but do you think I can
>find a MAX3001E on Maplin or RS? Nope.
>
>Any recommendations for UK eletronics (internet)
>mail order companies?  This is hobby stuff for
>me though, not commercial.

Don't worry, just fill out a sample request on their web page, and
automagically you end up with a couple of samples through the post.

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2004\10\06@115733 by Mcgee, Mark

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Do you mean fill out a sample request on the RS web site?  Can't seem to see
one on there.

{Quote hidden}

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2004\10\06@142953 by Peter L. Peres

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On Wed, 6 Oct 2004, Mcgee, Mark wrote:

{Quote hidden}

1 LM324 will build you 4 level converters. Each is wired as: +input to
1.5V signal source, -input to 0.6V reference, output to mcu. The 0.6V
reference is a 1N4148 diode mounted cathode to ground and fed with 10k
from +5V in the anode. The anode is the 0.6V reference voltage.

Peter
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2004\10\06@180248 by Dwayne Reid

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At 05:05 AM 10/6/2004, Mcgee, Mark wrote:

>The FE33L temperature control unit that I am intending to use runs on a 1.5v
>supply, and hence, the clk, data, and 2 other control pins operate 1.5 v for
>high, and 0v for low signals.
>
>Is there a simple way (i.e. in an IC) to amplify these (non inverted) to 5v
>for the PIC to read?  I know I can use a transistor for each line, and invert,
>but I'd rather not invert the signals if I can help it.

The simplest discrete non-inverting method uses 1 NPN transistor and 3
resistors per line: E to input, B to voltage divider (10k to gnd, 22k to
+5v), C to PIC & 22k pull-up.  You have to make sure that the control
signals can sink at least 0.5mA - scale the resistors higher if not.

This is a simple common-base level shifter and works quite nicely for one
or two lines.  Any more and I'd probably do this with chips (LM339 or
LM324) instead of transistors.

dwayne

--
Dwayne Reid   <dwaynerspamKILLspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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2004\10\07@034614 by Alan B. Pearce

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>Do you mean fill out a sample request on the RS web
>site?  Can't seem to see one on there.

No on the Maxim web site.
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2004\10\07@053112 by Mcgee, Mark

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They seem to be US based.  Are they likely to send to the UK?

Regards,
Mark

{Quote hidden}

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2004\10\07@060101 by Jinx

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> They seem to be US based.  Are they likely to send to the UK?

Sure, they'll send anywhere. Especially where they already have
offices. My monthly Maxim newsletter ? Switzerland -> UK -> NZ !!

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2004\10\07@060212 by Alan B. Pearce

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>They seem to be US based.  Are they likely to send to the UK?

Yes I have received parts in the UK from them. It may take 2 or 3 weeks, but
they do send them. I suspect they get the local distributor to post them
locally.

The downside is that you will then be on their mailing list, and receive
lots of mailings about devices you will never use, so if there is a point
where you can show what you are interested in as product lines, it pays to
minimise your "interests" unless you really do want the paper through your
letter box..

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2004\10\07@061625 by Kev Pearce \(kevp.com\)

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The Maxim website is US based by they will send samples to UK addresses from
their UK office automatically.

I've done it several times and got the chips every time. Usually within a
week
In fac the Maxim office is in Reading and I have poped in and picked up
samples in person, but I had to request them on the website first.

Kev/.


----- Original Message -----
From: "Mcgee, Mark" <mark.mcgeespamspam_OUTcsfb.com>
To: "'Microcontroller discussion list - Public.'" <@spam@piclistKILLspamspammit.edu>
Sent: Thursday, October 07, 2004 10:31 AM
Subject: RE: [PIC]Voltage pull-ups for 1.5v signals? was Newbie help getti
ng s tarted


> They seem to be US based.  Are they likely to send to the UK?
>
> Regards,
> Mark
>
> > {Original Message removed}

2004\10\07@061856 by Mcgee, Mark

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Cool.

Ok, I've been on and ordered samples of MAX3001E and MAX232

Thanks for the info

Mark

> {Original Message removed}

2004\10\08@095454 by Howard Winter

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Mark,

On Thu, 7 Oct 2004 10:31:01 +0100, Mcgee, Mark wrote:

> They seem to be US based.  Are they likely to send to
the UK?

Yes, I received some samples from them recently.  They
aren't very fast, though!

Cheers,


Howard Winter
St.Albans, Herts


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