Altium365 Link

SS200 Breakout

Design

We have requested a more detailed datasheet from ClydeSpace and we are required to have an NDA signed in order to receive more details - this is in progress.

• The SS200 has a 5-pin DF52 socket - we can use these connectors (1 2) to connect it to the solar panel.
• We will need to put drill holes of size M1.2 x 0.25 (radius 0.6mm) into the solar board to mount the SS200.
• Need to determine what type of connectors we want to use to get sun sensor data to ACDS, then essentially just route the SS200 ports to the appropriate connectors - should be pretty easy.
• Could be a good idea to order these ASAP - they have a lead time of 3-4 months, we can work on the solar board during this time and have it ready by the time they get here.

Photodiode Breakout

Component Selection/Justification

Trying to emulate this schematic from Texas Instruments displaying a photodiode with TIA (transimpedance amplifier)

• Photodiode: Using the OSRAM SFH2430 photodiode. Chosen due to its use in the Dalhousie sun sensor board and in a research paper.
• Op Amp: Using the OPA320AIDBVR Op Amp. Chosen due to its use in the TI schematic above. This op amp is also unity-gain stable, has a high PSRR, and is specifically designed for applications with photodiodes (see Applications section of datasheet).
• ADC: Using the MCP3021 ADC. Chosen due to 10-bit resolution, other than that there wasn’t too much of a reason for choosing this specific component.

Various passive components were mostly selected based on inclusion in the UW Orbital Altium component library. I also tried to pick 0603 size components.

<aside> 💡 NOTE: the photodiode datasheet gives reverse current of ~6.3µA from an illuminance of 1000lx and the circuit is designed to max out at about double that, 12µA (ie. ~2000lx). The illuminance from direct sunlight is ~100klx. We will probably have to put some sort of mask between the light source and the photodiode to decrease the illuminance to a reasonable level.

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<aside> 💡 NOTE: The reverse current given in the photodiode datasheet accounts for a reverse voltage of 5V. In my schematic I’ve chosen to go with no reverse voltage (ie. photodiode is functioning in photovoltaic mode). This decision is based on the TI schematic referenced above. I also looked at the old Orbital solar board which has a similar design to mine and has a comparable feedback resistor (based on comparing photodiode current/irradiance values). If something on the board doesn’t work, I’d try flipping the photodiode and connecting 3V3 to the cathode (as shown in the schematic here).

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Schematic