PRELIMINARY INFORMATION - SUBJECT TO CHANGE

The ROVotron transmitter uses one or two Sony PS2 Dual Shock 2 controllers and a custom microcontroller-based interface to the tether. An RS-485 serial link is used for data transmission. A matching microcontroller in the ROV receiver decodes the serial command stream and returns telemetry data.

Transmitter box

The ROVotron transmitter is a clear plastic box which houses the following items:

• An RTX transmitter PC board
• An LCD display, 4 x 20 characters with backlight
• Switches (e.g., for arming and launching torpedoes)
• LEDs to indicate ROV status (e.g., torpedo launcher ready)

The front edge of the box has the following connectors:

• One or two DE-9S for PS2 controller(s)
• An RJ45 jack for the signal tether
• Four RCA jacks for audio and video outputs

The RTX board has the following onboard connectors:

• A 7 pin Molex for up to 6 switches
• A 5 pin Molex for up to 4 LEDs
• A 4 pin Molex for a third A/V feed
• A 6 pin Molex for a PIC programmer

Refer to the schematics Transmitter page 1 and Transmitter page 2 to follow along with the text below.

Tether interface

The tether is one 16 AWG zip cord plus one CAT-5 cable, since we only need three signal pairs: RS-485, video and audio. Fused 48V power to the transmitter box is sent over the fourth pair from the ROV to eliminate ground loops.

We use a standard RS-485 transceiver chip. The termination has a divide-by-3 function to reduce voltage swing, which also reduces power consumption and EMI generation. The receiver still sees 1.3V which is enough for the differential detector to work just fine over our cable length. The divider network can be changed or bypassed as needed.

PlayStation2 interface

The command transmitter uses a standard Sony PS2 DualShock2 controller or two. This device provides two joysticks, two button diamonds, two trigger button pairs and Select and Start buttons. It features an analog mode that provides pressure data from the buttons to allow their use as speed controls.

The interface to the PS2 controller has been figured out by nice pople such asCurious Inventor. It's an SPI interface. The pinout is shown below.

The pinout we use matches the pinout of the factory connector, which is unobtanium. So we cut it off and wire in a DE-9P.

Pin	Name	Dir	CPU
1	Dat	in	SDI
2	Cmd	out	SDO
3	MPwr	out	Vcc5 fused
4	Gnd	--	Gnd
5	Vcc	out	Vcc3
6	Atn	out	ATNA, ATNB
7	Clk	out	SCK
8	--	--	--
9	Ack	in	ACK

(Direction: out is to PS2 handset, in is from it.)

Microcontroller

The microcontroller is a PIC18F4523. This part was chosen for its large number of I/O lines including SPI and USART and its 12 bit ADC. It's also used in the command receiver. We use the SPI port for the PS2 handset and the USART for the tether signal. Eleven I/O pins are used for the LCD display. Six input pins and 4 output pins connect to switches and LEDs in the box via Molex connectors.

Power

The transmitter uses a buck converter to make 5V @ 0.5A from 48V. The A/V buffer circuit requires -5V, which is generated with a charge pump. The PS2 controller requires 3.3V, which is made with a linear regulator.

Video/audio receiver

The ROV transmits audio and video over twisted pairs on the tether signal cable. These signals are balanced differential signals to reduce crosstalk and interference from adjacent pairs, especially the power cable with its 10 Ampere switching transients.

The balanced signals are received by AD8130 line receiver chips, converted to single-ended signals, buffered by two AD8075 video buffers and passed out through two pairs of RCA connectors to the monitors.

PRELIMINARY INFORMATION - SUBJECT TO CHANGE

©2010 David Forbes Updated March 24