parallax lcd display pricelist

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I recently acquired some surplus Parallax SX28AC chips in DIP packages. After looking at the datasheet it seemed likely I could design an entire SOC meter around this single chip processor. As a result I took the leap and purchased an SX Key (USB) board which allows programming and in-circuit source-level debugging as well as some 50 MHz three pin resonators all from Parallax.

The original plan was to use only the SX28AC and a display. To do this I planned on using the Analog Comparator with one side connected to the CANH line and the other to a resistor divider set at a 3 volt level. I was not sure how well this would work since the idle level is 2.5 volts and dominant level is 3.5 volts. So for initial development I decided to remove this variable and just go with a standard MCP2551 CAN Transceiver. Once all the code is debugged and working I may go back and remove the MCP2551 and add the resistor divider.

Here is a dump from the serial port of the raw SOC CAN messages including CRC. The code handles all the CAN bit processing (de-stuff, Serial to Byte, and CRC checking). Only messages with good CRC are passed on for processing. The code has two CAN Frame buffers so one can be processed by the main code loop for display/serial dump while the other is being filled in by the interrupt driven receive routine. Flags prevent overrunning the buffers. CAN frames that come in while both buffer are full are skipped.

Here is the test board connected to the LCD display. There is a 10k pot sticking up to adjust contrast. With two lines of 16 characters there is room to show lots of information. This code version is showing SOC Percent, Gids number (my daughter wanted the 281 added to indicate the max value. The second line starts with the CAN Frame ID for SOC 0x5BC. Next I added trip/charge gauge. In this case it is showing the number of Gids that it took today to charge our Leaf back up to 80% (actually 82.2%, Blink said 3181 watts were used). While driving the number will be negative and show Gids used since the meter was powered on (car turned on).

The hardware I have built so far is just for testing to allow debugging of the code. Here is the box that will hold the final version of the hardware which will plug directly into the display pins (no orange jumper wires). The cover has already been cut and display mounted. The 5 volt switching supply is shown laying in the bottom of the box. The box is 4 3/8 by 2 7/16 by 1 1/8.

Here is the mounted display being tested to see what it will look like. It is still driven by the small test board. Note the attached SX-Key to the right of the test board.

The main code handles processing the next completed and good (CRC ok) CAN Frame that is waiting in one of the two buffers. It first filters based on Frame IDs which to dump to the serial port (5BC for now) and loads each byte into a send buffer and waits for it to be sent. After all the data is dumped the main code updates the 2x16 display based on what is in the CAN Frame buffer and when done marks the CAN Frame buffer empty and start over again when the next frame buffer is full.

Over the next few days I plan to build the final version of the board that plugs into the display and mount it and the switching power supply in the project box and wire in the CAN Cable. (Or it might be delayed a week or two due to an upcoming trip to Ireland.)

The CAN Cable is the most expensive part followed by the display, SX28AC and MCP2551 Transceiver. I don’t have a cost for 12v to 5v power supply since they came with some old phones.

With the switcher power supply I measure only 60 milliamp at 12 volts used to run the logic and drive the display. The SX28AC also supports a sleep function that may have some use do reduce the power rather than turn it off. If I can get the hardware to sleep rather than power off I could save data from one power/charge cycle to another. That could be of some use to display summary type information.

I can easily change my format to match what CAN-DO wants. My current dump format has all the frame data including the CRC bytes so I could check on the PC side to see if I was getting good frames. I also used it to debug my built-in CRC checker code. My format can be displayed with HyperTerminal where yours is an 11 byte binary format which needs a program to sync with and decode. I may even provide an option to change the format on the fly between the two. Yours is more compact and takes less cycles to send and is great for logging lots of data. Mine is good for a quick look to see that everything is still working.

I have added a timer to the display (not the black one the one on the screen) which counts up when the chip is powered on. This way you can easily see how long it takes to get some where or how long you have been driving/charging. (It has been running for 90 minutes now and is still in sync with the black reference clock.)

As for costs it is not much (not including the SX-Key which is $60 and only needed by the developer and to program the chip). The OBD2 CAN cable is the same one Gary uses in his kits and is $11.95 plus shipping. The SX28AC/DP is $2.95 p/s, resonator $1.10 p/s both from Parallax. I bought 2 MCP2551 chips (DIP package) on ebay for $5.50 free shipping. The display is $3.99 free shipping on ebay. So that totals about $22.74 plus some shipping for one unit parts with the cable being over half that amount.

To support sleep mode I used two output pins and a pull-up resistor. The LCD plus the backlight LED only draws 12 milliamps total. Well within the 45 milliamp limit of the SX28 output drivers. So I only needed to move the LCD power from the 5 volt rail to an output pin and drive the pin active to power up the display. Before I enter Sleep mode all the I/O pins are placed into input mode which drops power to the display.

The advantage of the Pot is it can be mounted away from the display at a location easier for the driver to reach. For now I have it Velcro’ed to the side of the center console near the seat. The final location might be on the left side in one of the blank switch caps for the Steering Wheel/Side mirror heaters. This way the display can be mounted above the rearview mirror but the control mounted much closer to the drivers hand.

The next screen I added was to display the battery voltage and amps with a horizontal power bar display on the top row. Again this was inspired (copied) from seeing Phil’s LeafScan. Since this is a character not graphics display there is always a space between characters. This turned out to be of use as it makes reading the actual value very easy. Each column of dots represents 1024 watts and there are 5 dots per character. So just count the characters and multiply by 5. One custom edge character is generated on the fly with a variable number of columns of dots.

The third screen I added today shows Motor RPM and Amps. The current documentation for Frame 1DA seems to show RPMs in ½ units but I can’t see that. The low order bit is always active so I just shift the RPM value right one and display it. Can any expert comment on this?

I am still using my original test hardware with a few resistors and a cap added for the new features. The next step is to build a smaller unit that will fit above the rearview mirror. In that one the logic board will mount directly to the LDC display board. I have the parts just need to solder it up.

Almost forgot, I will also be adding a second CAN Transceiver so I can monitor the CAR-CAN too. So selecting a screen can also software switch to the correct CAN interface for the data to be displayed.

I made a stop by Radio Shack the previous day and picked up a small blank PC board that looked like it would fit all the parts and fit behind the LCD with just a single cut. I also was looking for a multi colored LED to use as a power level indicator instead of having to keep looking down at the Power Meter circles.

Here is a full layout of the parts on the small PC board. The top of the board still needs to be cut down to just above the row of 100 mil I/O pins for the Display and CAN cable. Along the left edge is the pot to control LCD contrast, reset switch and RGB LED. Along the right edge is the four pin program/debug port, three pin connector the for the 50 MHz resonator and two pin serial port. The top has the 16 pin connector to the LCD display and eight pin connector to the CAN cable. The plan is to use Cat-5 cable (4 twisted pair, EV-CAN(2), Selector Pot(2), +12 volts, Ground, and future CAR-CAN(2)). There is room for one more MCP2551 CAN Transceiver if I decide to monitor the CAR-CAN too (not too likely as I need to externally select between CAN buses)

These two pictures also include a display on the mounting bracket that will be Velcro’ed above the rearview mirror and the OBD2 connector (very low profile).

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