The PSM is powered by either the USB connection (5V supplied by the USB host or powered HUB) or a standard 5.5mm OD/2.1mm ID barrel connector with 4-9 VDC.  The regulator can provide up to 500 mA of 3.3 VDC power.  USB power is protected from overcurrent by a resettable fuse.  There is no protection with barrel connection and you must be careful not to draw more than 500 mA. The PSM itself draws about 135 mA with the backlight on at full intensity.  The PSM current draw is only ~35 mA with the backlight off.  The FTDI FT232RL manages the USB connection.  It is configured for 5V logic in order to control the 5V power it can provide to the PSM.  But, there is also a 3.3 V output of the FTDI chip.  This is provided on the pin with the circle around it just above and to the left of the mini-USB connector shown in the photo above. There is a small proto area between the min-USB and 5.5 mm barrel connectors.  The hole with the circle around it, just above the barrel connector, is connected directly to the barrel connector power pin.  So, you can add a larger capacitor on this input voltage if you desire using this area.

The accelerometer has four different G ranges, but defaults to the most sensitive range of +/- 1.5 G.  This range is useful for detecting the orientation of the device.  If a larger range is required, two pins are provided for setting the range.  They are under the “G-Sel” label on the board. Since the ADC is 8 bit the X and Y axis read around 128 when the board is flat.  Note that there is some variation in this 0-G reading as specified in the datasheet.

A small IC chip controls the backlight intensity with an analog signal provided by one channel of a 2 channel DAC on the I2C bus.  The extra DAC channel is provided on the header shown.  The DAC is 8-bit and converts an input level from 0-255 into a voltage between 0 and 3.3 V.  The useful range of the backlight driver is less than that however.  Anything above about 1.25 V (setting of ~100) translates into full intensity.  To save power (especially in battery powered setups) it is a good idea to dim the backlight when not in use.

Having 8 free Propeller pins was a very important design consideration.  These can be used for a wide variety of applications.  With the PSM Accessory Board (currently in development, showcased at the Expo), these pins can be used to provide NTSC video, keyboard input, mouse input, and control a servo.  The Propeller pin numbers (16..23) are labeled on the header.

Two Propeller pins are used to generate stereo sound.  This is fed to a headphone amplifier that can deliver fairly high quality sound to regular headphones.

Propeller Forum member Rockiki has provided free (MIT licensed) code for the Propeller that can read and write files from a FAT16 formatted SD card (up to 2 GB).  The driver does not currently support directories so all files to be used must be in the root directory.  With the serial control app loaded, you can transfer files back and forth from the PC using the example Windows App provided.  The serial control application also shows how you can use the novel write-protect and card-detect circuits to detect if an SD card is inserted and to detect the position of the write-protect tab.

The main feature of the PSM is the integrated full color display.  The display is 320x240 pixels and has 18-bits of internal memory per pixel.  The pixel color information can be sent to the display either in 16 or 24 bits.  Pixel data can also be read from the display (rather slowly) as 16 bits. Windows .bmp images can be displayed using both the serial control and slideshow apps provided.  The drivers are currently optimized for the normal, 24 bit-per-pixel, image format, but most BMP formats can be displayed.

The PSM can run the amazing “Graphics Demo” with just a few, slight modifications.  The current driver can run the Graphics Demo in either the original 256x192 resolution, or can be increased to 320x240.  Because the LCD contains it’s own GRAM buffer, double-buffering in HUB RAM is not required.  This is a huge savings in memory and can allow for much larger programs even with the increased resolution.

With this Windows application and the serial control driver, you can try out many functions of the PSM using the serial connection provided by a USB cable.