The Critter Board is based on a single ARM7TDMI microcontroller, the Philips LPC2138. It is a powerful 32 bit processor with a good amount of flash (program) memory and RAM. It is a fast controller, capable of up to 60 MIPS. It has many peripherals, including analog to digital and digital to analog converters, making it especially suitable for audio work. The LPC2138 users manual is a great source of information on the microcontroller.
The Critter Board has all the passive components to support the LPC2138. Additional features make it convenient for audio work: a passive filter on the DAC to cut off signal energy above the Nyquist frequency, a volume control header (number 3 on the picture below), and a sound output header and RCA jack (numbers 2 and 6 on the picture).
Two versions of the Critter Board are available: one with an onboard flash memory chip, and one with a card socket allowing different flash chips to be plugged in. Whether the flash is used on the board, or plugged into the card socket, it is the same chip: the M25P40 from ST microelectronics. Examples are provided for interfacing to the flash.
The onboard crystal oscillator is 14.7456 MHz, and setting up the internal Phase-Lock-Loop, the Critter Board runs at 58.9824 MHz (4x Fosc).
The Critter Board has a single 3.3 volt regulator to power the board. The microcontroller and flash memory chip both run at 3.3 volts. There is a header (labled 10 on the picture) with four pins each for ground and Vcc (3.3 volts). Power input must be in the range of 5 - 9 volts. A 9 volt wall wart is a good choice. Anything higher, and the voltage regulator will start to get quite hot.
Pressing this button resets the processor.
This header provides a solderable connection to the audio output. It is useful if you want solder wires directly from the Critter Board to a power amp, for instance. One pin is ground, and the other is the audio signal (Aout):
The volume control header is 3 pins: GND, audio from processor (Araw), and audio output (Aout).
It allows a potentiometer to control the overall audio output level. Using a 50k pot, connect one end of the pot to GND, the other to Araw, and the wiper to Aout. By default there is a jumper soldered connecting Araw and Aout (as in the picture above) so that audio output is maximum. Remove the jumper to use this header.
Power LED should be on when the Critter Board is powered up.
This header provides a solderable connection to GND and Vin (9 VDC). Pinout:
Line level RCA audio output jack.
Standard 2.1mm power jack.
Flash memory cards can plug in here. Make sure the side of the card with the components on it faces towards the processor.
Two versions of the Critter Board are available: one that has the onboard flash memory chip and no card socket, and one that has the card socket but no onboard flash chip. It is always possible to add a card socket to the Critter Board, and this is the purpose of the solder jumper. Since both a socketed flash card and the onboard flash chip cannot be used at the same time, the solder jumper is used to select one.
For onboard flash, the jumper should be jumped (solder connecting both pads). If using flash cards, make sure it is not jumped.
This header provides four connections to GND and four connections to Vcc (3.3 volts).
I/O header 1 provides 16 connections to the LPC2138. Many of these pins have multiple functions which can be selected in software (such as ADC, UART tx/rx, general purpose I/O, etc). Check data sheet for more info. Here is the pinout:
This 6 pin header is where the USB programmer connects. Pinout:
I/O header 2 provides 5 additional connections to the LPC2138. Check the data sheet for more info on the specific pins. Pinout:
The status LED is connected to pin P0.31.