A Patchblock has two digital and two analog controls, a power switch, a battery, analog 3.5mm audio input and output jack, and two digital 5-pin connectors.
Processor and Audio Hardware
The microcontroller is an LPC1343 Audio output is done using an external 10bit dual channel DAC (MCP4812), amplified by a MAX4410 headphone amp. Inputs and outputs are DC-coupled, so it is possible to send and receive constant voltage levels. 
- ARM Cortex-M3 Processor, running at 72MHz
- 32kb on-chip flash memory
- 8kb SRAM
- 20 kHz audio sampling rate
- 10 bit audio sampling accuracy
To the left and right of each patchblock there is one male repspectively female 5-pin connector, so that a connection can be established between two Patchblock devices. The male connector serves an an input to the device, whereas the female connector serves as an output. Currently, the main use for such a connection is to transmit digital audio signals from one patchblock to another.
Digital Audio Signal Transmission
Three of the five pins are used to transmit stereo digital audio signals from one PatchBlock to another: The SPI is used to interface with the DAC chip. The 2channel 3pin interface is based on PWM, with one pin being ground. The value that is being sent is encoded in the duty-cycle of the PWM. The receiving block measures the pulse width and turns it back into the value. This allows super-fast communication that the chip handles in hardware. This also allows to sync the receiving block's DSP handler to the sending one's, by linking it to the rising edge of the pulse. This means you can only send two values per DSP cycle to another block, no arrays or other fancy data. 
The remaining two pins are used for MIDI IN and MIDI OUT on the female and male connector, respectively. This is achieved through the use of the microcontroller's built-in UART module. The MIDI Note In block can be used to work with received midi notes inside a Patch.
The battery is a 550mAh LiPo pack, and is expected to last about four hours at least. Measured power consumption of the device is about 80mA (it depends on how much processing is being done, and whether headphones are used or not).