3-26-2011 Notes of work done over the past week.

A component on the LCD breakout board is getting quite hot.  At first I thought I was putting too much voltage into the vBatt Pin and I was thinking about putting less voltage in.  As it turns out if I would have done this I would have made the problem worse.  Upon inspecting the board I realized the component that was getting hot to the touch was the voltage multiplier,  had I cut the voltage I would probably have made the problem worse,  or maybe even damaged the component.

As taken from the Sparkfun web page for the device (1):

+Vbat and the 3.3V input can be driven from the same regulated 3.3V source, but the device will draw more current than if the +Vbat input was driven from a higher source voltage.  For a given +Vbat input voltage, you can expect the current draw to be:

• 108mA @ 6V input

• 120mA @ 5V input

• 243mA @ 3.7V input (single Lipo cell)

• 324mA @ 3.3V input

In my original specification I called for a USB game pad to be attached to the LPC2418 as an input.  I had scoured the LPC2418 documentation and could not find any interface that would allow the Microcontroller to act as a USB host.  Finally I found that the LPC241X series supports USB client mode but does not support host mode (2)(3).  The project will have to be revised since the USB game pad will not be able to be attached.

Because the USB game pad will not work with the system some other form of user input will need to be arranged.  The design includes the accelerometer will be acceptable for directional game control, but does not seem ideal for allowing the user to 'select' or 'confirm' a choice.  Some kind of button seems like it would be the most natural way for the user to be able to interact with the device in certain ways.

The LCD breakout board has two buttons available on the device(1), but they are set below the level of the screen,  making them difficult to push, also, one of the buttons is close to the voltage multiplier - which is hot to the touch.  As they are, the buttons on the LCD board are not an ideal solution,  they would need to be modified if they would be used at all.  Another option is to buy an additional button or two and wire them to one or two of the ADC pins.  It may be harder to find buttons that fit over the buttons on the LCD board, but they would not get in the way of a case.  Other switches will be common and cheap, but could get in the way of creating a case for the system. (perhaps the buttons could be mounted horizontally under the LCD board so they don't stick out a lot)

If there is an extra ADC pin, it would be nice to pipe power to the accelerometer from an ADC pin instead of power.  That way it would be possible to only give power to the accelerometer when the system is ready for accelerometer input.

Before connecting the accelerometer, it would be nice to have strings printing to the screen for visual feedback.

LCD Breakout Page (1)
USB for LPCXXXX (2)
LPC241X Datasheet (3) Page 16