1. Non-interference with Arduino board metal USB connector.
With some shields, there is an interference problem in that the USB connector metal
shell on the Arduino board sticks up and shorts out circuitry on the shield.
You cannot push the shield down all the way into the stacking header pins.
In contrast, the OT-Proto1 Shield was designed so there is no circuitry directly
over the USB connector to short out.
2. Big Voltage Regulators.
Most Arduino boards have dinky surface-mount (smt) voltage regulators, that will quickly
overheat if Vin is more than about 7V and the load currents are more than 200 mA or so.
Also, many Arduino boards can supply only about 50 mA of current at 3.3V.
In contrast, the OT-Proto1 Shield has its own 5V [adjustable] & 3.3V regulators that
can provide upwards to 1 Amp of current without overheating.
For added heat dissipation, a heatsink can be installed beneath the TO-220 regulator.
Likewise, the 3.3V DPAK smt regulator has top and bottom pcb areas for heatsinking.
regulator power dissipation page for
The output voltage of the TO-220 voltage regulator on the OT-Proto1 Shield can be adjusted
to different levels. See the
regulator hacking page for details.
3. Arduino I/O Pin Protection.
The single point on Arduino chips most susceptible to accidental damage are the 20 or
so I/O pins.
Application of voltage > 5V to a chip with Vcc=5V can permanently damage the chip.
And people do this all the time.
The simplest way to safeguard against this is to use small-valued Rs in series
with the I/O pins, eg 150-330 ohms - these work in conjunction with the internal
clamping diodes on the Arduino chip pins to limit overvoltage damage.
The series-Rs actually protect against voltages > Vcc and < 0V, and also short-circuits
on the pins.
The OT-Proto1 Shield allows series-Rs to be easily wired to all Arduino I/O pins.
4. SPI SRAM or EEPROM Chip.
Arduino program sketches most commonly run out of SRAM before anything else, such as
code space. The ATmega328 chip on the Arduino-UNO has only 2 KByte of RAM.
The OT-Proto1 Shield has a socket to mount an SRAM chip (23LC1024) that will provide
an additional 128 KBytes of SRAM, and which can be accessed at upwards to 500
KBytes/sec using SPI commands.
Alternatively, a 128 KByte SPI EEPROM chip (25LC1024) can be plugged in.
Both chips will run at either 5V or 3.3V, and there are Arduino libraries available for
both - see Arduino Playground.
5. RF Transceiver Mounting.
The OT-Proto1 Shield can directly mount many types of XBee-compatible transceivers,
as well as NordicSemi nRF2401 and HopeRF RFM12/RFM22 transceivers.
There is a 2mm socket layout for the XBee devices, surface-mount pads for the RFMxx
devices, and an 8-pin header for the nRF2401 devices.
These devices all operate at 3.3V only, and cannot be powered from 5V.
Many host Arduino boards cannot supply enough current at 3.3V for the higher power XBee
devices, but the 1A regulator on the OT-Proto1 Shield can easily power any of these devices.
The RFMxx and nRF2401 devices interface to the Arduino SPI peripheral, while the XBees
connect to the Arduino Rx/Tx pins.
There is a special jumper-block, as well as built-in level-shifters, on the
Proto1 board to interface XBees.
See the OT-Proto1 schematic and
RF Module Info page for more details.
6. Audio Amplifier.
The OT-Proto1 Shield includes the basic layout for an LM386 audio amp chip, as well as
associated Rs and Cs, plus a 2-pin 3.5mm terminal block to connect an external speaker.
The LM386 inputs can be jumpered to Arduino I/O pins or other audio sources.