Reference voltage for TLC 2543 question
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Posts: 46,084
I am fairly new to Basic stamps. One of the reasons I went with the
stamp was the outstanding job that that Parallax has done putting
information on the web. Thanks guys!
I am trying to process analog voltages and obtained a TLC 2543 DAC.
How do I go about providing a reference for the chip? Can I use 5.0
volts from a 7805 voltage regulator, or 5v from the Stamp2 itself?
As I understand, The reference needs to be between 4.5 and 5.5
volts. If the voltage is stable, then I should be able to divide it
by 4096 to get the conversion of mV to counts.
The project
I am developing a controller for an environmental pump used to
recover groundwater from a well. I would like to set the intervals
that the pump is on and off according to how much water is in the
well.
For example, if there is 10 feet of water, then the pump might run
for
20 seconds then rest for 50 seconds and repeat. If there is 2 feet
of water in the well then the pump might operate for 10 seconds and
rest for 1.5 minutes. There would be 5 or 6 different intervals
programmed between these water depths. If the water was less than 2
feet, then the pump might shut down and wait till there was more
water.
One of the difficulties with pressure measurement is the high cost of
transducers that can be submerged. I found an inexpensive solution by
using a $30.00 differential pressure transducer (PX-26)from
www.omega.com which I will wire up, add a vent tube, and encase in
epoxy.
Any help with the reference question would be greatly appreciated. I
will post more as I proceed.
The next step is to rig up an amplifier to boost 100mV to 5 volts,
then wire up the TLC 2543 to the Stamp2, and write some code. I'm
sure my code will need some help.
Thanks to all on the list for being a great resource.
stamp was the outstanding job that that Parallax has done putting
information on the web. Thanks guys!
I am trying to process analog voltages and obtained a TLC 2543 DAC.
How do I go about providing a reference for the chip? Can I use 5.0
volts from a 7805 voltage regulator, or 5v from the Stamp2 itself?
As I understand, The reference needs to be between 4.5 and 5.5
volts. If the voltage is stable, then I should be able to divide it
by 4096 to get the conversion of mV to counts.
The project
I am developing a controller for an environmental pump used to
recover groundwater from a well. I would like to set the intervals
that the pump is on and off according to how much water is in the
well.
For example, if there is 10 feet of water, then the pump might run
for
20 seconds then rest for 50 seconds and repeat. If there is 2 feet
of water in the well then the pump might operate for 10 seconds and
rest for 1.5 minutes. There would be 5 or 6 different intervals
programmed between these water depths. If the water was less than 2
feet, then the pump might shut down and wait till there was more
water.
One of the difficulties with pressure measurement is the high cost of
transducers that can be submerged. I found an inexpensive solution by
using a $30.00 differential pressure transducer (PX-26)from
www.omega.com which I will wire up, add a vent tube, and encase in
epoxy.
Any help with the reference question would be greatly appreciated. I
will post more as I proceed.
The next step is to rig up an amplifier to boost 100mV to 5 volts,
then wire up the TLC 2543 to the Stamp2, and write some code. I'm
sure my code will need some help.
Thanks to all on the list for being a great resource.
Comments
its higher than vref-. For differential mode you need vref+ to be at least
2.5v higher than vref- though. Someone else mentioned that you need Vref+ to
be at least 2.5v in normal mode as well - though I cant seem to find that in
the datasheet (not suprising - I'm bad with datasheets).
To generate the reference voltage you have many choices.
1) (The cheapest way) Make a voltage divider from two resistors
Vout=Vin*R2/(R1+R2). Has the disadvantage of being imprecise - you have to
dig out a MM and check a pile of resistors to get the exact voltage you
want. As temperature varies, so will your reference voltage. The formula for
a voltage divider is Vout=V*R2/(R1+R2). So if you used two 1k resistors
you'd get 5*1000/(1000+1000)= 2.5 volts. If you used a R1=3k and R2=1k you'd
get 3.75V out - reverse them and you get 1.25 volts.
2) Simplest is to use a multi-turn Potentiometer to create a voltage
divider. Dial up the voltage you need( use a 20 or 25 turn version)
3) Next cheapest and somewhat more precise is to use a zener diode of the
appropriate value.
4) Better is a precision voltage reference - Something like the LM385 which
comes in several voltage flavours - 1.2, 2.5, etc. There are variable
versions as well.
5) Most expensive but fairly precise and easiest to obtain - combine the
above. Lets say you needed 4.096 volts and could only get a 4.5v reference
(precision or zener). Feed the 4.5v into a potentiometer and divide out
4.096 volts. If you find it difficult to hit the exact voltage, add
resistors to the input and ground sides of the pot to narrow down the range
the pot can put you. Gives you less change in voltage ouput per turn of the
pot.
>
Original Message
> From: waltb27707 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=yyw65dJJYnN1e04crqGNfmizcVib9jPeTrVvLDaHHY1UNa1tRC3nrnLp3zhpROwzR_O_ovwT7OnlzvFB8BDEbA]wbeckwith@m...[/url
> Sent: February 8, 2004 5:49 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Reference voltage for TLC 2543 question
>
>
> I am fairly new to Basic stamps. One of the reasons I went with the
> stamp was the outstanding job that that Parallax has done putting
> information on the web. Thanks guys!
>
> I am trying to process analog voltages and obtained a TLC 2543 DAC.
> How do I go about providing a reference for the chip? Can I use 5.0
> volts from a 7805 voltage regulator, or 5v from the Stamp2 itself?
>
> As I understand, The reference needs to be between 4.5 and 5.5
> volts. If the voltage is stable, then I should be able to divide it
> by 4096 to get the conversion of mV to counts.
>
> The project
> I am developing a controller for an environmental pump used to
> recover groundwater from a well. I would like to set the intervals
> that the pump is on and off according to how much water is in the
> well.
>
> For example, if there is 10 feet of water, then the pump might run
> for
> 20 seconds then rest for 50 seconds and repeat. If there is 2 feet
> of water in the well then the pump might operate for 10 seconds and
> rest for 1.5 minutes. There would be 5 or 6 different intervals
> programmed between these water depths. If the water was less than 2
> feet, then the pump might shut down and wait till there was more
> water.
>
> One of the difficulties with pressure measurement is the high cost of
> transducers that can be submerged. I found an inexpensive solution by
> using a $30.00 differential pressure transducer (PX-26)from
> www.omega.com which I will wire up, add a vent tube, and encase in
> epoxy.
>
> Any help with the reference question would be greatly appreciated. I
> will post more as I proceed.
>
> The next step is to rig up an amplifier to boost 100mV to 5 volts,
> then wire up the TLC 2543 to the Stamp2, and write some code. I'm
> sure my code will need some help.
>
> Thanks to all on the list for being a great resource.
>
>
>
>
>
>
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the
> Subject and Body of the message will be ignored.
>
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>
>
>
>
>
>
You can use the vReg on the BS2 or a seperate Vreg. It depends on how stable
the volatge is, and how accurate you need it. You can use a precision vReg
if you need the accuarcy/stability.
Jonathan
www.madlabs.info
>
> I am trying to process analog voltages and obtained a TLC 2543 DAC.
> How do I go about providing a reference for the chip? Can I use 5.0
> volts from a 7805 voltage regulator, or 5v from the Stamp2 itself?
>
> As I understand, The reference needs to be between 4.5 and 5.5
> volts. If the voltage is stable, then I should be able to divide it
> by 4096 to get the conversion of mV to counts.
>
>How do I go about providing a reference for the chip? Can I use 5.0
>volts from a 7805 voltage regulator, or 5v from the Stamp2 itself?
Yes, just tie ref+ to the 5 volt Vdd supply and ref- to Vss. The
power for the TLC2543 (pin 10=Vss and pin 20=Vdd) also attaches to
this supply. Later on you can try more elaborate reference supplies
for whatever reason.
>As I understand, The reference needs to be between 4.5 and 5.5
>volts. If the voltage is stable, then I should be able to divide it
>by 4096 to get the conversion of mV to counts.
If your Vdd is 5.00 volts, then each count is 1.2207 millivolts. The
Stampese math you need will convert counts back to millivolts. Use
the */ operator!
millivolts = adc_counts */ 3125
debug dec millivolts/10000,".",dec4 millivolts, "volts",cr
displays x.xxxx volts, for example 4.9987 volts. There is more about this at
http://www.emesystems.com/OL2tlc2543.htm
Also, there has been additional discussion of this part here--search
the archives.
-- Tracy