Which serial LCD to buy?

Every once in a while on the arduino forum, people ask about which serial LCD to buy so today I saw such a post again and wrote this reply. I am certainly biased towards this serial LCD issue as I make and sell the phi-panel family of serial LCDs and keypad panels myself but take whatever you consider as fair argument:

3 vs. 4 wires:
Some serial LCD comes with 3 wires, 5V, GND, and RX. Some comes with 4 wires, 5V, GND, RX, and TX. Some serial LCDs are just LCDs, i.e. an output device. So you don’t need to read back from it. This saves one line, the RX on your arduino. Some have both RX and TX for possibly these reasons:

• Update firmware could require two-way communication for verifying the firmware at upload.
• Read back from the LCD to see what’s on the display, don’t know why that’s important. Or read back type of serial LCD ie. serial number or model number so arduino knows there is a serial LCD connected.
• The serial LCD can connect to other things. Again, this is a link to my product: this phi-panel has either integrated or optional 16-key keypad. The user input on the keypad is processed then transmitted TO arduino RX while commands to control the LCD or keypad (say enable/disable multi-tap) or messages to display on the LCD are transmitted FROM the arduino to the LCD panel. This requires two-way communications.

Cost:
Some serial LCDs are cheap because they don’t have a processor on board. They are the I2C serial interface, which arduino can connect to. These are simply I/O expanders that give you 8 additional I/O ports, enough to run the LCD. The backpack has no intelligence. The arduino spends all the resources and does all the work and needs to drive the display with special libraries provided by the makers. I know of two sources besides ebay, adafruit, and our forum member fm. Since there is no processor on the LCD backpack, the solution is cheap.

The more costly serial LCDs have on-board processors that controls the display and in the case of my LCD backpack, also possibly senses other inputs, process them, or even run multi-tap input or other fancy stuff on the on-board processor so your main arduino doesn’t need to worry about those. Those are more expensive and frees up resources on arduino and are more or less swappable with other serial LCDs with on-board processors without ever needing special libraries. Among a few of the sellers, sparkfun, moderndevice, some ebay sellers, mine, etc. All have the same level of intelligence except for mine, which is also the lowest cost with most functions. That might explain why both sparkfun and moderndevice are not interested in carrying my serial LCD.

So my logical conclusion is to buy the phi-panel family of serial LCD for the lowest price (except for fm’s I2C backpack) and best functionality. The rest of them in terms of functionality are about 5,000 lines of firmware code behind.

Enclosing your project, the pursuit continues

In a previous post, I discussed my journey to enclose my projects. I have been thinking about this question for a while. Recently I developed my serial LCD keypad backpack, specifically to make the difficulty of creating a user interface goes away. Now it needs to be mounted. So I devised a plan to create a physical user interface with appropriate project box for LCD projects. Here is a finished picture, not too bad, right?

Here is a list of materials needed:

• Box enclosures brand enclosure from allied electronics
• Optional rubber protective boot
• 4*4 membrane matrix keypad
• 16X2 character LCD
• Optional serial LCD keypad backpack
• Some screws, nuts, and standoffs

Here is a list of tools needed:

• Dremel handheld rotary tool (includes a small cutter and a few abrasive disks)
• A couple of drills (1/16 and 1/4 inches or 1mm and 3.5mm)
• Utility knife or just a cutter
• LCD printout
• Screw driver

My choice of enclosure has an advantage:the enclosure has a 9V battery compartment :). If you decide to not buy my serial LCD keypad backpack, then there will be 20 wires between the front panel and inside the box, 8 for the keypad, and 12 for the display. You may want to use a ribbon cable or jumper wires. If you do get the backpack, you only need 4 wires instead of 20 plus the programming is much easier with the backpack. So your choice.

Cutting and drilling:

First, get a precise layout of your display including the PCB boarder, screw hole and size, and display area. I suggest you print it out on paper or draw it on paper. Make sure you check the actual display instead of solely relying on the spec sheet, which could be different from your display.

If you got the serial LCD backpack, you can download this file and print it out. Cut out one display diagram. Read this spec sheet, maybe it’s the same as yours so you can also use this file. Whatever way you get the layout, use double sticky tape and secure it symmetrically on the front of the enclosure, leaving some space above it, maybe 1/4 inch or 6mm.

Now use the dremel abrasive disk and carefully cut along the inner rectangle, or the dimension of your display’s viewable area, not the entire black frame. You want to be careful not to over cut. You can try to cut from the under side to help you remove the window. Once you’re done cutting, use a knife to free the four corners.

I messed up the top edge of the box a bit by getting the spinning chuck too close to the edge. No big deal. Now you can use the dremal cutting tool to cut the four corners. Here is the under side.

Now use the smaller drill bit to drill guidance holes at the screw holes. Then use the proper drill bit to open the hole up for your screws.

Now remove the printout and excess material. Mount the LCD to see how it looks like.

Here is the back side:

See the standoff on the enclosure? That is why you don’t want to cut the window too high.

A closeup on how I mounted the display:

Basically from top to bottom: nut, display PCB, standoff, then screw on the other side.

Now cut a slot at the bottom of the box top to allow the membrane keypad connection to pass inside the box:

Just don’t cut too low. Leave about 0.5 inch or 12 mm.

Then carefully remove the backing of the membrane keypad. Pass the connector through the slot and stick the keypad on to the box:

Tada! A good-looking box that you can use for anything! I am planning to add a GPS module inside of it and run a GPS logger with it. Please see the phi-2 shield page for the GPS project code.

Now the under side:

As you can see, the connector comes back up to about the bottom of the LCD. This way you can connect the LCD serial back pack easily without stretching the cable.

Later I will add an LCD backpack to the box. The box has enough space to hold a full-size Arduino UNO and some other stuff, plus a 9V battery compartment so you are all set for an exciting project.

Connecting:

If you don’t have an LCD backpack, I suggest you solder a female header on the back side of the LCD so you can run simple jumper wires between the LCD and arduino. For the potentiometer and LCD resistors, solder them inline. Also use jumper wires to connect the keypad to arduino. You will only have 4 free arduino pins left. Total of 20 arduino pins – 2 serial programming pins – 6 LCD pins – 8 keypad pins = 4 pins left.

Otherwise, use the LCD backpack and the 4 included jumper wires. The backpack only uses 2 arduino pins.You will have 16 free pins on your arduino.