• NP-41 Taking Shape

    Chris Chung03/08/2016 at 16:15 1 comment

    This is a new version of PCB design. There are actually two PCBs. The green head unit contains the LCD display and MCU. They keyboard part is in white PCB contains only the keys and the battery. This allows me to trial various keyboard designs.

    They are connected via header pins as shown.

    The whole unit "sinks" in a 3D printed case to allow for comfortable holding and operation.

    There is also an experimental keytop structure w/ 3D printed keys. I do prefer the bare PCB instead, as I do not have means to print key legends and the 3D keys are coarse. I might try another 3D design in the future.

    The calculator is basically operational. I am spending time to enhance the firmware. Mainly need to find ways to load extension modules. Will give updates in the future.

  • Engineering Unit #1

    Chris Chung10/11/2015 at 23:25 0 comments

    Got the keys working, will need more timing adjustment (scanning) as they are sometimes not very responsive.

    I am running this on a partially depleted coin cell at around 2.85V. A 3V battery will produce too much ghosting on the LCD.

    Will be designing a new PCB to move on. The charge pump still fails after 1/2 second. It drops to 1.66V instead of staying at 2.8V. I had tried different values and types of capacitors and still cannot get it to work. I had also ripped the capacitor pad off after excessive re-flows. Will include more options in a new PCB design for charge pump trials (also allows custom biasing to see if contrast can be improved.

    Also found out that the current design w/ the use of a port 9, I cannot assign the "ON" key the role of h/w interrupt after getting into deep sleep. So the current unit does not have a good power saving sleep scheme.

    I am just showing the video here as there is a lot of interest for it. My next PCB will just contain the MCU and LCD, plus a 9-10 pin connector to a keyboard. This will save cost at the current stage.

    The final unit (for this PCB) is a bit large for my liking. I was indecisive when doing the LCD and had chose to match the HP-41C LCD size. It appears that based on that the product is more likely a desk unit (a slim one though) instead of a pocket unit.

  • MEMORY LOST

    Chris Chung10/06/2015 at 00:23 0 comments

    This is the first message you will see on a HP-41C calculator. Or when you replace your battery and have the internal memory reset.

    I had assembled the a first prototyping unit. Took me two takes and a fired MSP430FR6989 MCU. I have not yet get the internal charge pump working so the LCD does not have the best contrast and have some ghosting issues.

    This is an important step in this project as it's a proof of concept.

  • Custom made LCD Glass testing

    Chris Chung10/01/2015 at 12:09 2 comments

    I ordered custom made LCD glass for this project. They are about the same size of the original HP-41C display. It's a 14 segment display w/ 12 digits.

    The LCD glass is made w/ 6 Mux and 1/3 bias. With 1/6 duty cycle the contrast is not the best but there are so many segments and my target controller for this project does not have enough segment pins for a 4 Mux.

    I have not yet make this into a PCB so I am testing drive the LCDs w/ a test rig setup of GPIO direct driving the display. Resistor arrays are used to allow for setting proper bias voltages.

  • 2015-08-19 Prototyping on TI LaunchPad

    Chris Chung08/19/2015 at 17:36 0 comments

    Video showing a test run, 9, sin, cos, tan and back for forensic test.

    And a "Cat 3" for internal functions. Some characters (like > and ?) was messed up and since fixed.