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Topic: 2 IC2 LCD's - Another one.. Sorry! (Read 11904 times) previous topic - next topic

floresta

Quote
I will say that if you do your homework and choose wisely
you can save a ton of money and get a quality equivalent or better product/service for  less money.


I wouldn't argue with that.

What happened here is that the OP bought some inexpensive boards that do exactly what they were advertised to do and they do it just as well as the more expensive boards.  What he didn't understand was that due to the design of the pc board he couldn't easily take advantage of one of the major features if the I2C interface, the ability to control several identical devices with the same two signal wires.

I admit that there is no guarantee that a more expensive board would have solder blobs, jumpers, or switches to permit changing the address but the likelyhood is higher.


On a mostly unrelated note I see that the SainSmart board is advertised as being for IIC / I2C / TWI.  For the uninitiated these are three different ways of expressing essentially the same serial interface technique.  Now you could construe this two ways so I offer it just as an observation.

(1) They are trying to dupe the unwary into thinking that the board can utilize any of three different serial interface techniques.

(2) They are trying to help the uninitiated who might not know that they can use the I2C interface even though the manufacturer of their microcontroller called it TWI to avoid a trademark or copyright infringement.


Don


bperrybap


I'm shure because I have some of those pcb's.

Micky

So do share.....
Are you saying that the A0, A1, A2 pins on the 8574 are not connected
to anything? Did you ohm it out?
Perhaps the chip has undocumented internal pullups on the address lines?
(I couldn't find anything in the TI or Phillips data sheets about it)

If that truly is the case, then it is a bit easier to change the address since
you can simply tack a wire from pin 1 to ground to change the A0 state to Low
and not have to disconnect the pin from the existing trace on the board.



On a mostly unrelated note I see that the SainSmart board is advertised as being for IIC / I2C / TWI.  For the uninitiated these are three different ways of expressing essentially the same serial interface technique.  Now you could construe this two ways so I offer it just as an observation.

(1) They are trying to dupe the unwary into thinking that the board can utilize any of three different serial interface techniques.

(2) They are trying to help the uninitiated who might not know that they can use the I2C interface even though the manufacturer of their microcontroller called it TWI to avoid a trademark or copyright infringement.[/color]

Don

Even worse, many of the low cost PCF8574 boards boards will say:
IIC I2C TWI SPI Serial.
http://www.ebay.com/itm/New-IIC-I2C-TWI-SPI-Serial-Interface-Board-Module-Port-For-1602-LCD-Display-/251265752582?pt=LH_DefaultDomain_0&hash=item3a809b1e06
Those are clearly misleading (WRONG) since they don't have have SPI or what most people think of as "Serial".

--- bill


floresta

Quote
Perhaps the chip has undocumented internal pullups on the address lines?


Wouldn't they then designate the base addresses as 0x27 and 0x3F?

Don

bperrybap


Quote
Perhaps the chip has undocumented internal pullups on the address lines?


Wouldn't they then designate the base addresses as 0x27 and 0x3F?

Don

I wouldn't think so.
The data sheets that I've seen show how the address is formed with the A0, A1, A2 pins
using a base address.
They never state whether they have pullups/pulldowns on them.
(I always assumed that they needed to be driven one way or the other)
But, if the chip  happens to have internal pullups, it really wouldn't affect the base address
it would just set a "default" address to 0x27/0x3f if the pins happened to be
unconnected.


--- bill

cjdelphi

http://www.sainsmart.com/sainsmart-i2c-adapter-for-arduino-1602-1604-2002-2004.html

On the 2 I2C/LCD (in 1)


US $3.76
http://www.ebay.com/itm/5V-IIC-I2C-TWI-1602-2004-Serial-LCD-Module-Display-Adjust-Adapter-For-Arduino-/390545994871?pt=LH_DefaultDomain_0&hash=item5aee5af477


and
$12.00
http://www.sainsmart.com/sainsmart-i2c-adapter-for-arduino-1602-1604-2002-2004.html


The cheapy, $3.76 has the Addressing as people have pointed out, A0, A1,A2.

So the cheapy is better?... as it supports multiple addressing, my boards probably no doubt are identical to the OP's boards, and there is no
A0 - A2 pins or pads or anything...

BUT

It does use the same identical IC to do all the multiplexing, so is it not a simple case of finding which pins they are and getting the soldering iron out?

bperrybap


It does use the same identical IC to do all the multiplexing, so is it not a simple case of finding which pins they are and getting the soldering iron out?

Yes. That is what people are talking about in
responses: #10, #18, #19, #25, #26, #28, & #31.

Mike said it first in post #10
But all of these responses are talking about modifying the board
to change what is connected to pins 1, 2, & 3 of the PCF8574 chip
which control the i2c address.

--- bill

-Micky


Are you saying that the A0, A1, A2 pins on the 8574 are not connected
to anything? Did you ohm it out?
A0, A1 and A2 has contact but only to GND. But you need contact to VSS too to change the address. A0, A1 and A2 has contact to GND that means that they use address 0x20 or 0x27. Don't know which kind of chip they use.


Micky



Grumpy_Mike

Quote
A0, A1 and A2 has contact but only to GND.

That is being connected to something it is ground.
You need to make one of those lines connect to 5V.
Either there are some solder links on the board you can break or failing that lift the leg of the device and solder a wire to it connected to 5V.

Is the board the same as the one here:-
http://arduino.cc/forum/index.php/topic,162293.0.html

-Micky


floresta

Quote
But, if the chip  happens to have internal pullups, it really wouldn't affect the base address
it would just set a "default" address to 0x27/0x3f if the pins happened to be
unconnected.

That makes sense, the base address and the default address are two different concepts.  

Bill already mentioned the need to know how the backlight is dealt with. Aren't we also still missing some more key information that should be spelled out either on the sellers web page or on the (missing) documentation for the pc board.  It seems to me that we still need to know which I/O pins on the chip are connected to which I/O pins on the LCD module?  Without this information it is not intuitively obvious (at least not to me) how you can use the board without a lot more detective work.


Don

bperrybap



Are you saying that the A0, A1, A2 pins on the 8574 are not connected
to anything? Did you ohm it out?
A0, A1 and A2 has contact but only to GND. But you need contact to VSS too to change the address. A0, A1 and A2 has contact to GND that means that they use address 0x20 or 0x27. Don't know which kind of chip they use.


Micky




ok, and that makes sense for the board/conditions you describe in your thread:
http://arduino.cc/forum/index.php/topic,162293.0.html
given *your* i2c address is 0x20.
However, in this thread, Dexter said that his address is 0x27 not 0x20.
So I don't think your boards are the same as Dexter's or at least don't
have the address lines strapped the same.

There are too many conversations going on in this thread.
While the overall problem/issue is definitely the same,
I think we need to focus on what Dexter wants/needs in this thread since it is his thread
and leave talk about Micky's boards in Micky's thread. Just MHO.

That said, regardless of how the address lines are wired, both boards (Dexter's and Micky's)
can be fixed in the same way by lifting the leg of pin 1 and soldering it to a wire that
connects to either ground or VCC depending on which way it needs to change to
alter pin state from what it is now, which changes the address.
This is what Mike said in response #10, and again in #37.
Dexter's board will need the wire soldered to ground to change A0 from 1 to 0
which should change the i2c address from 0x27 to x26.


--- bill





Are you saying that the A0, A1, A2 pins on the 8574 are not connected
to anything? Did you ohm it out?
A0, A1 and A2 has contact but only to GND. But you need contact to VSS too to change the address. A0, A1 and A2 has contact to GND that means that they use address 0x20 or 0x27. Don't know which kind of chip they use.

Micky

All the 8574 chips I've seen, insert A2,A1,A0 as the lower 3 bits of address. In order to get
0x20 all three have to grounded and to get 0x27 all three have to be pulled up.
Regardless, Mikes suggestions in responses #10 and #37 still apply.



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