Will this shield connect 2 lcd displays to arduino?

Hey people!

I am a newbie here concerning arduino. I stumbled upon this product after searching a way to connect 2 LCD displays to one arduino board.


As you can see in the 2nd pic, the LCD display is connected to the black port on the right of the shield. Next to it is another one that looks exactly the same.. Would it host another lcd? So you can have 2 of them?

And what shield is that??

Then I found this also.. this shield also has 2 LCDs connected to it. It looks a bit different though. https://www.google.gr/search?q=serial+lcd+shield&rlz=1C1CHTH_elGR463GR464&um=1&ie=UTF-8&hl=el&tbm=isch&source=og&sa=N&tab=wi&ei=S38_Ut_5M6bA0QXAt4A4#facrc=_&imgdii=_&imgrc=SsGe1Eb3zjRd1M%3A%3BteUPmfO_JTlt-M%3Bhttp%253A%252F%252Fwww.emartee.com%252FImages%252Fwebsites%252Femartee.com%252FT2axVBXnhaXXXXXXXX_!!94851079.jpg%3Bhttp%253A%252F%252Fwww.emartee.com%252Fproduct%252F42052%252FSerial%252520LCD%2525201602%252520Shield%252520V2.0%252520%252520Arduino%252520Compatible%3B500%3B375

And what shield is this?

I also read somewhere that you can connect 2 LCDs on the Arduino Mega without a shield or a breadboard. because it hase more pins. Is that true?

Thanks for your help guys!!

All the best!

OK, you are getting altogether confused on this matter.

LCD displays are interfaced by four control lines and eight data lines. It is generally much more convenient (because displaying data on a LCD is essentially never time-critical in computer terms) to use the mode of the HD44780 whereby you only use four of the data lines and you generally ignore the Read/ Write control as you only choose to write to the controller, so you require seven lines to control it.

You may also wish to control the LED illuminating backplane if you are operating from battery power (or my solar co-generation system does this to conserve the last couple of watts!) which requires a switching transistor as the backplane draws much more than the 20mA for which the Arduino ports are rated, making eight control lines.

OK, so you can use eight outputs to control one LCD display. The trick is that one of the control lines is a select line, and the controller only responds when the controller is selected, so you only need one extra line to add each subsequent display (or an extra one if you wish to control the backlights separately, though this sounds improbable).

The "LCD shields" do this, connecting the LCD by eight control lines. There is an alternate approach however.

You can use a PCF8574 I2C expander chip to resolve an I2C interface into eight port bits. This is exactly what the "backpack" on the LCD you first cite, uses to interface with the LCD module to which it is fitted, so you now need only two lines to control the LCD. (It is rather interesting that these "backpack" boards using the same PCF8574 chip cost one sixth of the price of a board performing much the same function sold as an I2C port expansion!)

Even more convenient, is that quite a number (theoretically, up to 128?) of I2C "slave" devices can be controlled on a single 2-line I2C bus by selecting different addresses. The PCF8574 can if implemented on the "backpack" board (and it usually is,) be selected to have one of eight possible addresses, so you can run up to eight LCD displays, each having the I2C "backpack" fitted and the address selected (by jumpers on those six feed-throughs you see below the contrast potentiometer on the "backpack").

The I/O shield in that picture with lots of connectors is quite unnecessary - you connect all the I2C controlled LCDs in parallel. You can in fact, connect even more such displays if you ever needed to by implementing (as it is in software) further I2C interfaces to re-use the same range of addresses.

The PCF8574A can have 16 addresses because it has one more address bit and there are IIC port expanders that can give you even more devices on one Two Wire pair.


Sorry ... but that's wrong! Both the PCF8574 as well as the PCF8574A have only 3 accessable address pins. Therefore both can only be configured to 8 different addresses. The confusion about this in most cases caused by a diagram in the datasheet of the PCF8574 that shows the address range for the PCF8574A contains 8 bits instead of 7 bits as for the "normal" PCF8574. But that's not the right. The 8th bit is ALWAYS the direction bit (read/write) and is NOT part of the address.