Deep-Sea Data Connect Design Notes
P. McGill

* WiFi provided by two Ubiquiti Networks BulletM2-HP devices to send/receive data
+ According to Dave French, BM2HP is functional at 12 V, ~125 mA, which is 1.5 W.

* ROV side
SSID: ROVbulletm2
Pass: rovbulletm2

Admin over Enet at 192.168.1.20
User: ubnt
Pass: mbari

* Camera side
SSID: Camerabulletm2
Pass: camerabulletm2

Admin over Enet at 192.168.1.21
User: ubnt
Pass: mbari


* System also needs to power Raspberry Pi 3B+, which needs 5 V, 500 mA, which is 2.5 W. Turning off the LEDs, HDMI video, and WiFi can reduce this to ~350 mA, but we'll use worst-case numbers. We need to measure the current while running VirtualHere USB server.

* Total power is about 4 W. If this is supplied at 12 V, we need to switch at least 333 mA. A reed switch rated for 1 A DC should do it. There will be some losses in the DC-DC converter that converts the battery voltage to the 5 V the RPi needs, but there's plenty of margin on the current rating. A suitable switch may be the Littelfuse MLRR-4-12-18.

* Alternatively, can use Pololu 15 V Step-Up Voltage Regulator U3V70F15 found here:
https://www.pololu.com/product/2896

+ As purchased, the U3V70F15 enable pin has a 100 kΩ pull-up resistor on the board and an 800 kΩ pull-down resistor internal to the switching regulator IC (part number unknown). To disable the regulator, the enable pin must be pulled to ground.

+ We want the regulator to be enabled by the closure of a normally open reed switch and off otherwise, which is the opposite behavior. To allow this, remove the 100 kΩ pull-up SMD resistor from the board, and move that 100 kΩ resistor to bridge between the enable and ground pins of the board to pull down the enable input harder. Connect the reed switch between the enable and Vin pins to turn on the regulator. In this configuration, the regulator draws 34 µA at 10 V. In a year this would consume 8760 h x 0.000034 A = 0.30 Ah.

* Powering the system with a 3S string of Electrochem 3B0035-PD D cells would provide 3 x 3.3 V x 12 Ah = 119 Wh. At 4 W (not accounting for converter efficiency), this would last 30 h. We already buy such a battery from Electrochem for Smith's camera tripod, and the Electrochem part number is 3PD1517. It has an open-circuit voltage of 11.7 V and delivers most of its power at 9.9 V

+ At 10 V input, the Pololu U3V70F15 regulator is about 95% efficient, so we'd get about 119 Wh x 0.95 = 113 Wh. At 4 W load this would last 28 h.

+ At 15 V input, the Coral Macro Cam system draws 390 mA, which is 5.85 W

* System was deployed on Ricketts dive #1426 on 3Mar22.