Cage Camera (A3034)

© 2018 Kevan Hashemi, Open Source Instruments Inc.

Contents

Description
Power Supply
Design
Development

Description

The Cage Camera (A3034) is provides a camera for monitoring small animals in cages. The A3034A is a rectangular circuit board that spans the width of a mouse cage, supported by four legs on its corners. The A3034A cameer is at the center of the board, looking down into the cage, and equipped with a fish-eye lens. Around the edge of the circuit baord are twelve white LEDs and twelve infra-red LEDs that provide variable illumination. An embedded computer on the circuit board provides continuous upload of compressed video over TCPIP, as well as illumination control over TCPIP. The entire circuit runs on a single 24-V power input, and communicates through one RJ-45 socket over a local area network.


Figure: Cage Camera (A30234X). The power socket is on the top-left. The Ethernet cable plugs into the Rasberry Pi embedded computer, but comes off the board with the help of a cable tie on the top-left. The length of a mouse cage would be left-right underneath the A3034 in this view, along with the length of the Animal Location Tracker (A3032).

The A3034 is designed to operate in a faraday enclosure. Here is the A3034X installed over an Animal Location Tracker (A3032) in an FE2F faraday enclosure, with a plastic tub representing a mouse cage.


Figure: Cage Camera (A30234X) and Animal Location Tracker (A3032C).

In the photograph above, the A3034X is supplied with power with the help of a power feedthrough at the back of the enclosure with a black power cable. Its Ethernet connection enters through an RJ-45 feedthrough with a blue cable. The red cable is the ALT (Animal Location Tracker) platform's LWDAQ root cable. This cable passes through an RJ-45 feedthrough in the back of the faraday enclosure and then to a LWDAQ Driver (A2071E). The gray cable is the logic cable that connects the ALT to an Octal Data Receiver (A3027). The ALT gets it power from its LWDAQ cable. On either side of the platform are two Loop Antennas (A3015C). Their coaxial cables leave through BNC feedthroughs at the back of the enclosure, and so connect to the A3027 antenna inputs.


Figure: Wide-Angle Lens Beneath A3034X.

The A3034X camera uses a 1640 × 1232 pixel CMOS image sensor manufactured by Sony Semiconductor and a high-resolution wide-angle lens. The photograph above shows the DSL215, which provides a 120° field of view. We also equip the A3034 with the DSL219 lense, which provides almost as wide a field of view, but contains its own distortion-canceling optics. Both lenses can view an entire mouse cage when just above the rim of the cage base.

Power Supply

The A3034 requires its own 24-V power supply. We use the same power adaptor we provide with the LWDAQ Driver (A2071E) and Command Transmitter (A3029C). The power socket is marked +24V on the printed circuit board. The power plug is 5.5 mm outer diameter and 2.1 mm inner diameter, with the inner contact positive.


Figure: Power Adaptor. Connect 100-250 VAC, 50-60 Hz with a computer power cable. These power supplies are generic, here is an example data sheet.

We bring this 24-V power into a faraday enclosure with a power jack bulkhead connector. The power socket of the connector faces outward and receives the plug of the power adaptor. Within the enclosure, the cable attached to the bulkhead connector plugs into the A3034.


Figure: Power Cable and Bulkhead Connector.

The A3034 will operate at full performance for input voltages 18-24 V. For a 24 V input, when streaming livem, compressed video with ambient lighting, the A3034 consumes 100 mA. When we turn on the visible LEDs to full power, the current consumption increases by 30 mA. When we turn on the infrared LEDs, the current consumption increase by 40 mA.

Design

S3034_1: Cage Camera Schematic.
A303401A.jpg: View of A303401A printed circuit board.
A303401A.zip: Gerber files for printed circuit board version A.

Development

[25-MAR-18] We assemble the first prototype A3034A with circuit board A303401A. At power-up, the white LEDs shine brightly for less than a second, then go out. Two resistors over heat and burn. We find that U1, the current mirror, is suffering from thermal run-away. Our original circuit runs 2 mA through U1-6 at maximum brightness and expects 2 mA to flow through U1-3 as well. The two transistors are in the same SOT-323 and our assumption was they would remain at the same temperature. If U1-3 heats up, we expect U1-6 to heat up too, dropping its base-emitter voltage, and so controlling the current through U1-6. The base-emitter voltage drop for a given collector current decreases with temperature by roughly 2.4 mV/°C, as we show for diodes here. We find that for currents larger than 500 μA into U1-6, the current through U1-3 increases during the first few seconds. The LEDs turn off because U1-3 drops below the minimum 18 V reqired to provide current to the LEDs through Q2 and Q3. Instead, current flows through the base junctions of Q2 and Q3 into U1-3. When we have 20 mA flowing through U1-3 and 10 V, current dissipation in U1-3 is 200 mW, which exceeds the maximum for the UMX1 dual transistor.

[26-MAR-18] We change R1-R4 to 100 kΩ, 50 kΩ, 27 kΩ, and 14 kΩ respectively. At full brightness we have 400 μA flowing through U1-6. We remove Q3. We are powering only D1-D6. We have R6 = 270 Ω and R5 = 2.2 kΩ. We observe 1.7 V across R5, which implies 770 μA through U1-3. We do not have thermal run-away, but we have the U1-3 current is twice that of U1-6, which implies that the junction of U1-3 is around 7°C hotter than that of U1-6 (VT Ln(770/400) ÷ 2 mV/°C ≈ 7 °C). The voltage across R6 we assume is around 1.7 V also so we have 6.3 mA flowing through the white LEDs. If Q2, a ZXTP2025F has typical current gain of 380, we expect base current Q2-3 to be 20 μA ≪ 770 μA. We could decrease R6 to 100 Ω and so increase the LED current to 10 mA. The power dissipation in R6 will then be 10 mW, which is fine.

[27-MAR-18] We have R1-R4 all driven by the same 3.3 V and their resistance in parallel is 7.2 kΩ. The voltage across them all is 2.7 V for a current of 370 μA. Base-emitter voltage drop is 0.61 V. We have R6 = 100 Ω. Voltage across R5 = 2.2 kΩ is 1.5 V for 680 μA. Voltage across R6 is 1.4 V for 14 mA. We remove R6 and still see 1.5 V across R5, suggesting the base current drawn by Q2 is negligible.

We replace R1-R4 with a single 18 kΩ and see 2.8 V across it for 150 μA. We have R5 = 5 kΩ and 0.8 V across it, so 160 μA. The voltage across R6 = 100 Ω is also 0.8 V for 8 mA into the LEDs. We load Q3, D7-D12, and R7 = 100 Ω and see 8 mA flowing into the new diodes. The voltage drop across both chains of LEDs is 16 V for average forward drop of 2.7 V per diode. We load 5 kΩ for R15 and 18 kΩ for R10, to which we connect 3.3 V. We load D15-D26. We get 8 mA through the twelve infra-red diodes. Pin Q5-1 is at 15 V, making the average forward drop of the diodes 1.25 V.

We test the visible and infra-red illumination for image-taking in a cage. The visible illumination is bright. Our visible LED is the white L130-2780 of the Luxeon 3014 series. It is a 2700K warm white emitter in a P1206 package. The infra-red illumination is too dim for us to obtain a blob image of a toy mouse. The infra-red is the XZTHI54W. It is an 880-nm emitter in a P0805 package. According to its data sheet, this LED should emit a minimum of 2π × 0.8 mW = 5 mW of infra-red light at 20 mA forward current, or 2 mW at 8 mA. We drop R14 from 100 Ω to 27 Ω and R10 from 18 kΩ to 10 kΩ. We now see 1.0 V across R14, so 37 mA flowing through LEDs. The LED forward voltage is now 1.38 V. We put an SD445 photodiode up agains one of the LEDs and get 3.4 mA ÷ 0.6 mA/mW = 5.7 mW of infra-red light for an input power of 50 mW, or 11%. We drop the current to 10 mA and see 1.9 mW or 13%. We try an HSDL-4400 with 37 mA and get 4.1 mW. We restore the original LED. Our white LEDs at 8 mA give us photocurrent 2.8 mA. Assuming an average wavelength of 500 nm this is 11 mW. The electrical input power is 100 mW, so efficiency is around 11%.

[04-APR-18] We choose new DAC resistor values R4 = 40.2 kΩ up to R1 = 316 kΩ for the visible light control and R13 = 20.0 kΩ up to R10 = 160 kΩ for the infra red light control. Assumiung the U1 and U2 base-emitter drop is around 0.6 V and the logic HI is around 3.3 V, we expect the following control currents versus DAC count.


Figure: Control Current versus DAC Count. The visible light control current flows into U1-6. The infrared control current flows into U3-1.

Assuming that the control currents are mirrored exactly by U1 and U3, we calculate the visible and infra-red LED current versus DAC count. We have R5 = R15 = 4.7 kΩ, R6 = R7 = 100 Ω, and R14 = 27 Ω.


Figure: Expected LED Current versus DAC Count. The visible light current flows through two parallel chains of LEDs.

The maximum forward current of our infra-red LED is 50 mA. We expect to be just under the maximum at 44 mA for full brightness. The maximum current through the white LED is 120 mA and our maximum current is 6 mA. We remove our photodiodes D13 and D14 and replace them with phototransistors one hundred times more sensitive to light, and set R8 = R9 = 20 kΩ.

[13-APR-18] We have two A3034X, W0381 and W0382. We are shipping W0381 to ION along with ALT V0385. The Rasberry Pi username is pi@10.0.0.234 and password is "osicamera".


Figure: Shipment 2048, A3034X and Accessories.

In the figure above we see two Ethernet cables and an RJ-45 feedthrough to carry the Ethernet connection from a local area network hub to the A3034X. The power adaptor is in a white box, and its bulkhead connector is in a bag. We have standoffs to raise and lower the camera, cable ties to fasten the Ethernet cable to the circuit board, extra flex cables for the camera connection, and wider-angle lens for use with the camera.