high power to low power GPO ?

VJ · Post by VJ » Wed Dec 10, 2003 8:27 am

Hello,

I'm still planning how I intend to setup an LCD; I'm thinking along the lines of digital potentiometers controlled by low power GPO (I tend to prefer this over PWM, and it requires a bit of DIY

).

On an MX2, there are a number of fan headers. Is it possible to configure them to act as low power GPO's ?
Or should I be on the lookout for another model which has a larger number of low power GPO's ?
(I would prefer USB connectivity though)

J

Post by **Henry** » Wed Dec 10, 2003 10:46 am

The MX2 which is a LK202-24-USB can have it's fan headers set to 5V, with no current limiting though.... so yes, with the MX2 you can have 6 low power GPOs

3x 5V 1000mA max
3x 5V 20mA max <--- current limited be resistors.

VJ · Post by VJ » Thu Dec 11, 2003 1:17 am

Henry wrote:The MX2 which is a LK202-24-USB can have it's fan headers set to 5V, with no current limiting though.... so yes, with the MX2 you can have 6 low power GPOs

Ok, Thanks!

Just to make sure: the MX2 (thus LK202-24-USB) is the model with fanheaders in stead of "regular" GPO's (the manualpage over on http://www.matrixorbital.com/manuals/LK ... USB_01.pdf still mentions regular pins for all GPO's).
Is it also by means of a jumper (i.e. without having to solder) ?

J

Post by **Henry** » Thu Dec 11, 2003 10:37 am

sorry, my mistake... the LK202-24-USB just has the standard headers, if you wish to purchase the one with fan headers, fire off an e-mail to sales when you place your order and they will make sure you get the rev 1.4

VJ · Post by VJ » Fri Dec 12, 2003 2:38 am

Henry wrote:sorry, my mistake... the LK202-24-USB just has the standard headers, if you wish to purchase the one with fan headers, fire off an e-mail to sales when you place your order and they will make sure you get the rev 1.4

But the fanheaders can still be switched to lowpower (so the only difference is the shape of the GPU) ?

J

Post by **Henry** » Fri Dec 12, 2003 10:35 am

VJ wrote:
Henry wrote:sorry, my mistake... the LK202-24-USB just has the standard headers, if you wish to purchase the one with fan headers, fire off an e-mail to sales when you place your order and they will make sure you get the rev 1.4

But the fanheaders can still be switched to lowpower (so the only difference is the shape of the GPO) ?

J

Paradigm · Post by **Paradigm** » Fri Dec 12, 2003 1:32 pm

Depending on what you're doing you could do it that way, but a FAR easier way to get a digital pot up would be the Maxim DS2890 1-Wire Digital Potentiometer and use the 1-Wire interface on the MX series. It can work with upto 11V and be anywhere from 0 to 100K in 256 steps. If you need more voltage/current I can easily post a op-amp circuit for you.

VJ · Post by VJ » Sun Dec 14, 2003 12:47 pm

paradigm wrote:Depending on what you're doing you could do it that way, but a FAR easier way to get a digital pot up would be the Maxim DS2890 1-Wire Digital Potentiometer and use the 1-Wire interface on the MX series. It can work with upto 11V and be anywhere from 0 to 100K in 256 steps. If you need more voltage/current I can easily post a op-amp circuit for you.

Oooh...
That would be interesting!

(I haven't got experience with those 1-wire interfaces, but wouldn't mind picking up on it)

J

Paradigm · Post by **Paradigm** » Mon Dec 15, 2003 11:03 am

Well if you're interested you could read the specification in:

http://pdfserv.maxim-ic.com/en/an/appibstd.pdf

Or if your just looking for lots of docs, check:

http://www.maxim-ic.com/an_prodline2.cfm/prodline/21
http://www.maxim-ic.com/an_prodline2.cfm/prodline/22

And all of Maxim's 1-wire parts can be found at:

http://www.maxim-ic.com/1-Wire.cfm

And feel free to post any questions here too.

VJ · Post by VJ » Tue Dec 16, 2003 1:53 am

paradigm wrote:Well if you're interested you could read the specification

Yes, I have been checking out those documents...

The 1-wire interface of the MX-series, where is it located ? (I can't seem to find it on the LK202-24-USB pdf manual)
Can it be addressed using LCDC or is other software needed (if so, how can it be addressed) ? Apparently, the DS2890 supports multiple units on a single bus (which would be very interesting).

Could you also post that op-amp circuit ?

Thanks!

J

Paradigm · Post by **Paradigm** » Tue Dec 16, 2003 9:49 am

I'll get the opamp circuit up sometime this afternoon. I'll have to dig it out of text book first

The 1-wire are the 3-pin connectors on the edge of the board. They are ONLY on LK202-24-USB PCB v1.3 and greater. Each 1-wire device (no matter what it is) has a unique serial number. This allows you to connect any number of 1-wire devices to a single bus (in theory). In fact the theoretical maximum number is 4,503,599,627,370,496

. But before that happens space/electrical constraints will kick in.

Don't know about using LCDC to address a custom 1-wire applicaiton. You'd have to ask mat-d-rat in the software section. However anything that can send/receive commands via RS232 can access the 1-wire bus. I think I posted a tutorial on the MX2 1-wire bus. I'll look around for it, and if I can't find it, I'll post another one.

Anything else?

EDIT:

Ok, I found a web page which actually does has a little demo:

http://www.vwlowen.demon.co.uk/java/opamp.htm

Select "Non-inverting" as the type and set both Ra and Rf to 500 ohms (or anything equal). Enter 1 for V1 and hit calculate. You'll see that you get a 2x Vgain. So if you feed 1V in you get 2V out. If you want a gain of 1 (Vin = Vout) then set the Rf to 0 ohms, aka a wire.

The point of the op amp is that it will draw next to no current from your digital pot, AND, it can amplify the signal too since the digital pot can only handle 11V.

I'd use an LM741 or equivalent. If memory serves me right they *should* be able to suplly enough for a fan, but I'm not sure. But hey, the worst you'd do is melt the 741

.

VJ · Post by VJ » Fri Dec 19, 2003 1:32 am

paradigm wrote:Don't know about using LCDC to address a custom 1-wire applicaiton. You'd have to ask mat-d-rat in the software section.

Ok, will do!

However anything that can send/receive commands via RS232 can access the 1-wire bus. I think I posted a tutorial on the MX2 1-wire bus. I'll look around for it, and if I can't find it, I'll post another one.

That would be great!

The point of the op amp is that it will draw next to no current from your digital pot, AND, it can amplify the signal too since the digital pot can only handle 11V.

I'd use an LM741 or equivalent. If memory serves me right they *should* be able to suplly enough for a fan, but I'm not sure. But hey, the worst you'd do is melt the 741 .

Ok, so the amount of amplifications is determined by the Ra and Rf resistors... right? But do I need that much amplification for a 12V fan ?

I checked the LM741 specs: http://www.national.com/pf/LM/LM741.html , but it is unclear how to connect them together... I would assume I only need pins 2,4 and 6 (the circuit then resembles that from the link you posted).
(sorry, I know some of the basics, and tinkering around with things like this seem the ideal way to learn more)

J

Paradigm · Post by **Paradigm** » Fri Dec 19, 2003 11:18 am

Ok, so the amount of amplifications is determined by the Ra and Rf resistors... right? But do I need that much amplification for a 12V fan ?

Not much, but since the digital-pot can only handle 11V, you will need a little.

I checked the LM741 specs: http://www.national.com/pf/LM/LM741.html , but it is unclear how to connect them together... I would assume I only need pins 2,4 and 6 (the circuit then resembles that from the link you posted).

For the LM741

Pin 1 - No connect
Pin 2 - Ground
Pin 3 - The input
Pin 4 - Ground
Pin 5 - No connect
Pin 6 - Output to fan
Pin 7 - 12V
Pin 8 - No connect

For the DS2890, you need the 6-pin TSOC pacakge. And for it:

Pin 1 - Ground
Pin 2 - 1-Wire bus
Pin 3 - 5V
Pin 4 - 6V <- I'll explain
Pin 5 - to the input of the LM741
Pin 6 - ground

The 6V is nice because then you can have Rf and Rb the same value and get the 2x amplification to 12v. Now the trick is getting 6v. Well the maximum resistance of the digital pot is 100k. So if connect Pin 4 to 12v through a 100k fixed resistor. When the digital pot is at 100k (max) the voltage at pin 5 will be 6 volts. When the pot is at 0, the voltage will be 0v. Instant 0-6v generator. Then connect that to the 741 to get 2x amplificaiton, you end up with 0-12v.

I'll see if I can get this all in schematic form by this afternoon and attach the post. The text will have to suffice for now.

(sorry, I know some of the basics, and tinkering around with things like this seem the ideal way to learn more)

It is the best way. If you have any questions, just keep asking them.

Edit:

An image is worth a thousand words:

WARNING: I haven't tested out the previous circuit. I haven't dealt with this subject matter for a while. I know for fact (now) that the LM741 will NOT be able to supply the current for a fan. I'm looking into alternative power op-amps but the basic principle is still the same. Stay tuned for a replacement part for the 741.

Edit #2:

The TCA0372 from motorola would fit the bill. It is a dual-op amp (2 op-amps in one pack) and it has a peak output current of 1.5A (as long as you don't hit the peak too often

) Anyway, the changes for the TCA0372DP2 are:

LM 741 Pin 2 -> TCA0372 Pin 5
LM 741 Pin 3 -> TCA0372 Pin 6
LM 741 Pin 4 -> TCA0372 Pin 4
LM 741 Pin 6 -> TCA0372 Pin 3
LM 741 Pin 7 -> TCA0372 Pin 2

And ground every other pin on the TCA0372DP2. There are other package variations (DW and the DP1) just change the pins accordingly.

VJ · Post by VJ » Tue Dec 23, 2003 4:16 am

Wow... Thanks!

J

VJ · Post by VJ » Sun Dec 28, 2003 11:34 am

Hello,

As you said, the TCA0372 is a dual opamp, judging by its diagram (and pinconnections) it seems only one of the present opamps is used. Can I use the other one for another similar circuit ?
(i.e. use 1 TCA0372 and 2 digital pots to drive 2 fans)

J