The Video Critter 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. The LPC2138 users manual is a great source of information on the microcontroller.
In addition to the passive componets to support the LPC2138, the Video Critter provides hardware for synthesizing a composite NTSC or PAL video signal.
In order to produce color video signals with as few components as possible, we have clocked the microcontroller at a multiple of the color-burst frequency. For NTSC the color-burst frequency is 3.579545 MHz, and we use a 14.31818 MHz. Sockets are provided so different crystals may be plugged in for PAL operation.
The Video Critter has a single 3.3 volt regulator to power the board. The microcontroller runs at 3.3 volts. There is a header (labled 13 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.
The Video Critter comes with a 14.31818 MHz crystal for NTSC operation. This may be replaced with a PAL compatible frequency.
7.5 - 9 volt input jack. Standard 9 volt wall wart works well.
Line level audio output on RCA jack.
Power connection to Vin.
The volume control header is 3 pins: GND, audio from processor (Araw), and audio output (Aout). The connection nearest the audio output jack is Aout, the center is Araw, and the connection furthest from the jack is GND. 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.
These headers provide direct access to the video hardware. The are useful for debugging low level video stuff.
On when the board is powered up.
This LED may be controlled in software. It connects to pin P0.31 on the microcontroller.
This is where the USB programmer attaches.
A 16 pin header for interfacing switches, LEDs , or other sensors. The pinout:
1: P0.2
2: P0.3
3: P0.4
4: P0.5
5: P0.6
6: P0.17
7: P0.8
8: P0.9
9: P0.10
10: P0.11
11: P0.12
12: P0.13
13: P0.15
14: P0.16
15: P0.18
16: P0.19
Many of these pins connect to the many peripherals of the LPC2138, such as analog to digital converters. Check the LPC2138 datasheet for more info.
An RCA jack for video output. The video signal is scaled for a 75 Ohm load (composite video input standard).
Power connections. Useful for connecting external circuitry (buttons, pots, LEDs).