trigger stamp with low voltage? is it possible?
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Posts: 46,084
Hi,
I'm fairly new to using STAMPs so this is probably
a very newbie question.
I'm trying to get the stamp to recognize a 1.2 volt signal
as a trigger. essentially, if it sees 1.2 volts on pin 0
then it should kick off other programs, and do it's thing.
otherwise it should just sit there and wait.
I thought I could look for high on the pin, but due to the source
I can't up the voltage that it is sending out.
Also, I'm not sure if it makes a difference, but when the 1.2 volt
signal goes out, it stays on for about 5 seconds. I don't know if
that would throw things off or not.
thanks for any help you can give me.
-Jeff
I'm fairly new to using STAMPs so this is probably
a very newbie question.
I'm trying to get the stamp to recognize a 1.2 volt signal
as a trigger. essentially, if it sees 1.2 volts on pin 0
then it should kick off other programs, and do it's thing.
otherwise it should just sit there and wait.
I thought I could look for high on the pin, but due to the source
I can't up the voltage that it is sending out.
Also, I'm not sure if it makes a difference, but when the 1.2 volt
signal goes out, it stays on for about 5 seconds. I don't know if
that would throw things off or not.
thanks for any help you can give me.
-Jeff
Comments
I'm fairly new to the STAMP thing myself, but I've been reading Scott
Edward's book, and from that, I'm pretty sure the high/low threshold
for the stamp pins is 1.5 volts. Someone please correct me if I'm
wrong.
Newbie answer: you might be able to use a switching transistor to
have the lower voltage turn on another power source that would
overcome the 1.5v threshold?
Josh
Great info in this group, btw. I've been lurking for some time now
and thought I should contribute... I hope I gave the right answer.
--- In basicstamps@yahoogroups.com, "js5752 <jds@t...>" <jds@t...>
wrote:
> Hi,
> I'm fairly new to using STAMPs so this is probably
> a very newbie question.
>
> I'm trying to get the stamp to recognize a 1.2 volt signal
> as a trigger. essentially, if it sees 1.2 volts on pin 0
> then it should kick off other programs, and do it's thing.
> otherwise it should just sit there and wait.
>
> I thought I could look for high on the pin, but due to the source
> I can't up the voltage that it is sending out.
>
> Also, I'm not sure if it makes a difference, but when the 1.2 volt
> signal goes out, it stays on for about 5 seconds. I don't know if
> that would throw things off or not.
>
> thanks for any help you can give me.
>
> -Jeff
above/below 1.20000 volts.
If you need technical help on this SIMPLE comparitor circuit, write back.
[noparse][[/noparse]Non-text portions of this message have been removed]
>I'm trying to get the stamp to recognize a 1.2 volt signal
>as a trigger. essentially, if it sees 1.2 volts on pin 0
>then it should kick off other programs, and do it's thing.
>otherwise it should just sit there and wait.
Is the signal you are trying to trigger from a low impedance signal? In
other words, will it sink a small current while at a logic 0?
If so, a single silicon diode and 1 resistor may be all you need. The
diode acts as a level shifter and lifts the input signal UP by about
0.6V. This turns your input signal into a 0.6V or 1.8V signal and will
operate the stamp input quite nicely. FYI, the input threshold of a Stamp
pin is about 1.4 Vdc.
Connect the diode in series with the input signal: cathode (stripe) end to
the input signal, anode to the stamp pin. Also connect a 10k resistor from
the stamp pin to Vdd (+5V).
The resistor is necessary to pull the stamp pin HI. The value is not critical.
Hope this helps!
dwayne
--
Dwayne Reid <dwayner@p...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(780) 489-3199 voice (780) 487-6397 fax
Celebrating 18 years of Engineering Innovation (1984 - 2002)
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commercial email nor is intended to solicit commercial email.
Stamp to see the input as high. Can you drive an LED or lightbulb with your
1.2 volt signal? This would provide other options.
What is the source of the signal?
Original Message
> I'm fairly new to using STAMPs so this is probably
> a very newbie question.
>
> I'm trying to get the stamp to recognize a 1.2 volt signal
> as a trigger. essentially, if it sees 1.2 volts on pin 0
> then it should kick off other programs, and do it's thing.
> otherwise it should just sit there and wait.
>
> I thought I could look for high on the pin, but due to the source
> I can't up the voltage that it is sending out.
>
> Also, I'm not sure if it makes a difference, but when the 1.2 volt
> signal goes out, it stays on for about 5 seconds. I don't know if
> that would throw things off or not.
Original Message
> Typically it takes a higher voltage, I think about 2.6 volts or so, for
the
> Stamp to see the input as high. Can you drive an LED or lightbulb with
your
> 1.2 volt signal? This would provide other options.
>
> What is the source of the signal?
>
>
Original Message
>
> > I'm fairly new to using STAMPs so this is probably
> > a very newbie question.
> >
> > I'm trying to get the stamp to recognize a 1.2 volt signal
> > as a trigger. essentially, if it sees 1.2 volts on pin 0
> > then it should kick off other programs, and do it's thing.
> > otherwise it should just sit there and wait.
> >
> > I thought I could look for high on the pin, but due to the source
> > I can't up the voltage that it is sending out.
> >
> > Also, I'm not sure if it makes a difference, but when the 1.2 volt
> > signal goes out, it stays on for about 5 seconds. I don't know if
> > that would throw things off or not.
volt...then capacitively couple the signal you are monitoring onto the ST^AMP
pin with the 1 volt level. The added 1.2 volts from your source would then
drive the STAMP pin high momentarily. Obviously you must have the STAMP in a
loop looking for this signal change at all times so you don't miss it.
[noparse][[/noparse]Non-text portions of this message have been removed]
--- In basicstamps@yahoogroups.com, "js5752 <jds@t...>" <jds@t...>
wrote:
> Hi,
> I'm fairly new to using STAMPs so this is probably
> a very newbie question.
>
> I'm trying to get the stamp to recognize a 1.2 volt signal
> as a trigger. essentially, if it sees 1.2 volts on pin 0
> then it should kick off other programs, and do it's thing.
> otherwise it should just sit there and wait.
>
> I thought I could look for high on the pin, but due to the source
> I can't up the voltage that it is sending out.
>
> Also, I'm not sure if it makes a difference, but when the 1.2 volt
> signal goes out, it stays on for about 5 seconds. I don't know if
> that would throw things off or not.
>
> thanks for any help you can give me.
>
> -Jeff
low voltage detection is possible with a fe inexpensive parts. rather than
give you a long expanation, let me suggest you get the January issue of
Poptronics, which has a nice piece on LM339 circuits. If you don't want to
purchase it, just Google " LM339 circuits antd I'm sure you'll get a bunch of
hits.
Larry
In a message dated 12/19/02 3:26:37 PM Pacific Standard Time,
basicstamps@yahoogroups.com writes:
> Date: Thu, 19 Dec 2002 15:47:03 -0000
> From: "js5752 <jds@t...>" <jds@t...>
> Subject: trigger stamp with low voltage?
> is it possible?
> Hi,
> I'm fairly new to using STAMPs so this is probably
> a very newbie question.
>
> I'm trying to get the stamp to recognize a 1.2 volt signal
> as a trigger. essentially, if it sees 1.2 volts on pin 0
> then it should kick off other programs, and do it's thing.
> otherwise it should just sit there and wait.
>
> I thought I could look for high on the pin, but due to the source
> I can't up the voltage that it is sending out.
>
> Also, I'm not sure if it makes a difference, but when the 1.2 volt
> signal goes out, it stays on for about 5 seconds. I don't know if
> that would throw things off or not.
>
> thanks for any help you can give me.
>
> -Jeff
>
>
[noparse][[/noparse]Non-text portions of this message have been removed]
Use a voltage comparitor if you want to trigger off of 1.2 volts.
This is the simplist and most reliable way to do it. All this other voltage
divider stuff I read, diode and resistor, blah blah blah,is not worth the hassle
if you want to precisely trigger at 1.2 volts.
The comparitor circuit is extreemly easy to make. From the replies I have seen
on this subject, there are only a few that recommended an op amp comparitor,
that is there are only of few real electronics guys - the other suggestions
appear to come from programmers, not that there is anything wrong with
programmers, I am amused at times when I read some of the hardware
suggestions.....
I tried using a 741 but something must have gone wrong, because
I could never get it to trigger at the right level.
If someone could show me what I should be doing,
that would be terrific.
thanks
-Jeff
--- In basicstamps@yahoogroups.com, smartdim@a... wrote:
> You can use an op amp comparitor to make either logic 0 or logic
1
> above/below 1.20000 volts.
>
> If you need technical help on this SIMPLE comparitor circuit,
write back.
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
[noparse][[/noparse]Non-text portions of this message have been removed]
LM329 (Radio Shack has them). This has 4 comparator op amps. You don't
need a negative supply, just ground and 5V.
1) Use a voltage divider to get a, say, 1V signal from 5V (a 5:1
divider). Use a pot if you want to adjust it.
2) Connect this reference to the + or - terminal of the comparator
3) Connect the input voltage to the other comparator terminal
4) Put a pull up resistor on the output of the comparator (say, 10K to
5V) and connect the output to the Stamp input.
Now assume that the input voltage is 0V. The output of the comparator
will be either 5V or 0V. If you don't like the way it is, swap the leads
on pins 2 and 3. In reality, you can figure out which way it will go
ahead of time, but it is easy enough to correct for in software or swap
the wiring, so do whatever is easiest.
When the input voltage exceeds your reference (1V), the output of the
comparator will change state. Don't set the reference too close to the
actual level or the output may flip back and forth (oscillate). Then
you'd need hysterisis to prevent this. Better to just pick a lower
number.
If you don't like guessing how the output will be, here's the rule: If
the - input is greater than the + input, the output will go to 0V (well,
the negative rail, which is 0V in this case). If the + input is larger,
the output simply disconnects (that's why the pull up resistor is
important). There are technical reasons why this is better than letting
the opamp supply 5V, but that's a long story.
If you need divider help, read http://www.wd5gnr.com/basiccir.htm.
Generally, pick a current you want to draw (say 1mA). 1V at 1mA is 1K
ohms. So the resistor between the op amp input and ground should be 1K.
To get 1mA to flow at 5V you need a 5K total resistance. So since you
already have 1K, you are short 4K. So a 4K resistor from +5 to the input
will do the trick. That assumes the comparators input resistance is VERY
high (which it is). Of course, you probably have to settle for nearby
values (I don't think 4K is a standard value; sure you could make one
with 4 1Ks, but at 5% 3.9K or 4.3K would probably do fine (10% would be
3.9K).
If you want to learn more about op-amps, read
http://w1.859.telia.com/~u85920178/begin/opamp00.htm (Harry is a smart
guy) and/or http://www.wd5gnr.com/opampneg.htm. Also, be sure to read
the Art of Electronics for just about everything. Read my review of it
at http://www.wd5gnr.com/books.htm.
By the way... It would be pretty common to use an NPN transistor like a
2N2222 for this. The only problem is a 2N2222's Vbe can (worst case) be
1.2V so without knowing the conditions the circuit will be under, this
would be a marginal design. In practice it would probably work, but it
would "invert" the signal (no problem to handle in software).
The idea would be to ground the emitter and connect the collector
through a resistor (Rc). The Stamp would connect to the collector also.
The input would go to the base through a resistor (Rb). We don't know
how much current your 1.2V source can supply, but let's say it is
plenty. We can drive the 2N2222 into saturation by putting a small
resistor for Rb. The base will try to be at 0.7V (nominally; like I
said, could be as high as 1.2V in which case this won't work). So the
base current should be about (1.2-0.7)/Rb or .5/Rb. So if Rb were 50
ohms you'd drive 10mA into the base. That would draw the collector down
towards ground (how much depends on a lot of factors, but a large enough
Rc (100K?) should allow it to drop below the Stamp's threshold. Ideally,
you want to drive the transistor into saturation, but with the marginal
voltage I wouldn't count on that. Unless I was really bent to use a
transistor, I'd go with the op amp. If the input were a larger voltage
(say 12V) I'd be tempted to use the transistor.
Oh well, been a long time since I've written a long winded post, so
hopefully the list will forgive me.
AND... Happy holidays to all on the Stamp List! Hope you get lots of
gadgets under your tree (if you observe the tree thing, anyway).
Regards,
Al Williams
AWC
* NEW: PAK-VIa - Read PS/2 keyboards or mice -- double the buffer, lower
current consumption.
http://www.al-williams.com/awce/pak6.htm
>
Original Message
> From: js5752 <jds@t...> [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=VcqdwNtn72t0O1rXlgpWWsssnMsmQVTnqnQTeiwOrJnFCm76RWzbiXR8fCUEf3NTccXDGVKZtkCT]jds@t...[/url
> Sent: Friday, December 20, 2002 6:14 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: trigger stamp with low
> voltage? is it possible?
>
>
> Actually I could use some help on this "SIMPLE" circuit.
> I tried using a 741 but something must have gone wrong,
> because I could never get it to trigger at the right level.
>
> If someone could show me what I should be doing,
> that would be terrific.
>
> thanks
> -Jeff
>
> --- In basicstamps@yahoogroups.com, smartdim@a... wrote:
> > You can use an op amp comparitor to make either logic 0 or logic
> 1
> > above/below 1.20000 volts.
> >
> > If you need technical help on this SIMPLE comparitor circuit,
> write back.
> >
> >
> > [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
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