Many LCDs and OLED have a 7 or 8 x 2 DIL connector rather than 14 or 16 SIL which makes them incompatible with using the axe132 as a direct backpack. Also, many have reported that the axe132(133) can lose characters when driven directly from a hardware serial output (hserout) without pauses between characters. Finally, the axe132 does not have hardware to switch a backlight on and off. I decided to develop a fully compatible alternative to overcome these shortcoming but still use a cheap reprogrammable picaxe as the processor.
The 08M2 doesn't have enough output ports so the next chip in-line pricewise was the 14M2 so this was chosen. To use this it is necessary to run the display in 4 bit mode. Hardware serial input was used to get the benefit of the two byte buffer on the M2 chip but on the M2 chip the hardware serial port does not support data inversion. This meant externally inverting the incoming serial input to maintain compatibility using a transistor. A second optional transistor drives the backlight via a shorting link or a user selectable resistor (to control the backlight current.
The fixed resistors on the board are surface mount but are the large easily solderable 1206 size. For OLED use the variable resistor is not required. The picaxe is a conventional socketed PDIP.
The software has been optimised to the best of my ability to ensure that characters are never lost with the single exception that a pause of 20msec (allow 25msec for 20 char wide displays) must be inserted after a command to display a stored message (command 253,mnum).
Full details of the design (DesignSpark) including gerbers and the code together with a test program are included in the attached zip file. For reference I had 10 of the PCBs made up in China for a total cost of £19.49 including P+P.
The picture shows the module with minimum components populated to support a 16 x 2 OLED.
The 08M2 doesn't have enough output ports so the next chip in-line pricewise was the 14M2 so this was chosen. To use this it is necessary to run the display in 4 bit mode. Hardware serial input was used to get the benefit of the two byte buffer on the M2 chip but on the M2 chip the hardware serial port does not support data inversion. This meant externally inverting the incoming serial input to maintain compatibility using a transistor. A second optional transistor drives the backlight via a shorting link or a user selectable resistor (to control the backlight current.
The fixed resistors on the board are surface mount but are the large easily solderable 1206 size. For OLED use the variable resistor is not required. The picaxe is a conventional socketed PDIP.
The software has been optimised to the best of my ability to ensure that characters are never lost with the single exception that a pause of 20msec (allow 25msec for 20 char wide displays) must be inserted after a command to display a stored message (command 253,mnum).
Full details of the design (DesignSpark) including gerbers and the code together with a test program are included in the attached zip file. For reference I had 10 of the PCBs made up in China for a total cost of £19.49 including P+P.
The picture shows the module with minimum components populated to support a 16 x 2 OLED.
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