I ship all orders on Monday and Thursday mornings and I will send you a confirming email for each order. At the present time I can only ship to the 48 contiguous United States. Note: There is no minimum order, but in order to provide parts for as many people as possible, there is a maximum order of $100. In addition, no more than 10 of any one item may be ordered at one time. Orders that exceed those limits will be automatically refunded.
Serial 8x2 LCD Board
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| LCD-08x2 in Action |
Serializes a parallel 8-character by 2-line LCD: $6.95 each (Bare Board)
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The serial 8x2 LCD PC board was originally designed in conjunction with a PICAXE Primer column published in the June 2009 issue of Nuts & Volts magazine. If you are interested in the power and simplicity of PICAXE programming, you may want to subscribe to Nuts & Volts as we develop additional PICAXE-based projects in future installments of the Primer.
The PC board was specifically designed to match the dimensions of the Hantronix 8x2 displays with an 8x2-pin connector along the left edge of the display. For an example, see the Hantronix HDM08216L-3-L30S display, available at Mouser Electronics. This is a very common configuration for LCD displays and many "generic" displays will also fit properly on the LCD-16x2 board. To be sure the board will work with a specific display you have in mind, download the Dimensional Drawing for the Hantronix HDM08216L-3 display and compare its measurements to your display.
The LCD-08x2 board implements a PICAXE-14M circuit that provides the necessary hardware and software to accept serial input and convert it to the required data format of an inexpensive HD44780-based parallel LCD. (See the following circuit schematic.)
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| LCD-08x2 Schematic |
Each of the PC board's connectors requires a little clarification. First the "Prog" connector (labeled "Program Adapter" on the PC board) enables the 14M to be reprogrammed without having to remove it from the PC board. The pinout of the connector matches the standard that is used in all the PICAXE Primer projects. This pinout is also the same as that of the UPA-4x4 Programming Adapter available on this site (see the "Products" listing on the left side of the page). A sample program for the 14M (LCDdriver.bas) is available in the "Projects" section at the top of the page, but the real power of the LCD-08x2 board is that you can customize the driver to suit the needs of your individual projects. The 3-pin "Lo-Hi" jumper allows you to change between two different baud rates (which you can also customize in your own driver software) without needing to reprogram the 14M.
The "I/O" connector (in the center of the bottom edge of the PC board) also requires explanation. It's a 5-pin right-angle female header, but you use it by inserting a 4-pin straight male header between the female header and the breadboard. The male header needs to be long enough to make solid connections on both ends. (For example, see the first header in the "Headers" link on the left of the page.) In the above schematic, you can see that both "RxD" pins of the I/O header connect to the same pin on the 14M. This somewhat unusual arrangement is for the purpose of providing some flexibility in how the LCD is connected to a "master" processor. If you are using a 28X1 or 28X2 as your "master" processor, it allows you to connect the RxD input on the LCD-08x2 board to either "ser tx" (pin 17) or "out 0" (pin 21) on the master processor. This is accomplished by inserting the 4-pin male header toward one end or the other of the 5-pin female header, so that only one of the two "RxD" connections is actually made.
The two rows of five holes just above the I/O connector are for an optional 5x2 straight male header that can be used for a ribbon cabble connection if you need to locate the board some distance from your project. If you decide to include it, install it from the bottom of the board and solder the short ends of the pins on the top of the board as shown in the below photo of the complete board. On this header, each of the 5 pairs of pins is connected. In other words, on the other end of the cable you can use either (or both) of the 5-pin rows to connect your porject to the LCD-16x2 board.
Potentiometer R9 provides the contrast adjustment for the LCD display and resistor R1 is the current-limiter if you are using a backlit display (more on that shortly). The following photos show a bare LCD-08X2 board along with a fully-assembled board for comparison. (You can click on either photo to see a larger version.)
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| Bare LCD-08X2 | Completed LCD-08X2 |
As you can see in the photo of the completed board, there are a couple of parts that haven't been installed. The two pairs of holes at the bottom edge of the board were intended to be used by soldering in two 2-pin right-angle male headers that could be inserted into the breadboard for additional stability (there are no electrical connections to these pins). I have found that they really aren't necessary, but you may decide that you prefer to include them.
As I mentioned above, resistor R1 is the current-limiter in case you are using a backlit LCD display. Since the backlighting is LED-based, a current-limiting resistor is generally a necessity, but not always - sometimes it's built into the display. Unfortunately, you need to read the data sheet of the display you are using to determine the correct size of the current-limiting resistor and it's rarely stated directly. You need to find the values for two important specifications of the display and do a little arithmetic. The Hantronix data sheets, for example, state that the typical forward voltage (Vf) across the backlight is about 4v, and the maximum forward current (If) through the backlight is 120 mA. With a 5v supply, that leaves 1v to be dropped across the current-limiting resistor, so 1v / 120mA = 8.3 ohms as an absolute minimum safe size for the current-limiting resistor. To be conservative lets say 10 ohms, which I have on hand but didn't have the courage to try! Instead, I used a 27 ohm current-limiting resistor for my backlit Hantronix displays. Since 1v / 27 ohms = 37mA, I'm well within the limit and the displays are comfortably bright to view. If you use a different LCD brand you will need to do similar calculations to arrive at a safe value for your current-limiting resistor.
Important note: You need to exercise extreme caution when interchanging backlit displays on the LCD-08x2 PC board. For example, I have a very nice blue and white display that requires a 330 ohm current-limiting resistor. If I carelessly inserted it into an LCD-08x2 board with a 27 ohm resistor installed, powering it up would almost certainly fry it! So the safest approach for backlit displays is to first determine a conservative size for the current-limiting resistor, and then leave that display attached to its specific LCD-08x2 board. Of course, this caution doesn't apply to non-backlit displays, which don't even connect to pins 15 and 16 anyway.