University of LeicesterPLUMERef: PLM-SYS-ADCSInterf-601-1 Date: 19/08/2008

ADCS Interfacing

D.S.W.Gray

Date / Updated Reference Number / change
19/08/2008 / PLM-SYS-ADCSInterf-601-1 / first version issued


The ADCS system is a custom circuit using a single Honeywell HMC1053 chip to sense the strength of the magnetic field in three orthogonal axes in sequence.

Inputs and Outputs

Power will be supplied by the +5V_BUS, from pin H2.25 or H2.26. The ADCS will be connected to ground via pin H2.30. Axis address selection for the MAX9 and MAX10 are controlled via H2.20 and H2.22 respectively. H2.24 has been allocated for the -neutralising switch to turn off the reset pulse. The reset pin, H1.34, is shared with the transceiver socket as this is the only port on the system bus that has the level shifting to produce the 5V logic required. Power control is done by 3.3V logic through pin H2.10.

Analogue readings from the ADCS are taken from pin H2.6.

The ADCS must be inactive when the transceiver is active. To achieve this, a multiplexer is added to the cubesat kit system bus to shut off the reset line so that transceiver operations will not damage the magneto-resistor chip. The multiplexer is switched by 3.3V logic. Additionally a power FET is added with a further 3.3V logic input to shut off +5V power to the ADCS.

Input / Type / Bus Pin / OBDH Pin Name / ADCS Pin Name
Axis-Selection / 3.3V logic / H2.12
H2.14 / P1.4
P1.2 / P7
P6
Magnetic Set/Reset / 5V logic / H1.36 / n/a / P1
Data Out / Analogue output / H2.6 / P6.2 / P4
Switch Magnetic Set/Reset / 3.3V logic / H2.16 / P1.0 / n/a
Switch Power On / 3.3V logic / H2.10 / P1.6 / n/a
Power In / +5V / H2.26 / n/a / P2
Ground / GND / H2.30 / n/a / P3, 5 and 8

The ADCS connects directly on top of, or via a stacked configuration, to the MCU board via the cubesat kit system bus, which is a set of 104 PC/104 pin sockets in a block four wide and twenty six long. The two rows closest to the edge are on the H2 connector. The two rows next to this are on the H1 connector. The maximum rating of the PC/104 system bus is no more than 3A, and between -0.3 to 3.6V, except on the 5V logic pins. The operating temperature of the MCU is between -40 and +850C. PC/104 buses are stackable in that several can be fitted one on top of another. The ADCS cannot be on when the transceiver is active. This will cause a conflict of the reset pulse.

Stacking PC/104 boards

Power

The ADCS is powered by the +5V_SYS bus on pin H2.26, with GND on H2.30. This is controlled by a powerFET, switched by a 3.3V logic signal from pin H2.10. When operating the ADCS draws approximately 0.0385W. When off the ADCS draws 0.00125W. This is due to the multiplexer and powerFET.

Mass/ Mechanical

The ADCS circuitry will be mounted on a Printed Circuit Board (PCB) along with other custom subsystems. This board will be positioned in a stack of PCBs with the payload electronics board at the top and the MCU board at the bottom. The order of the stack depends on the masses of each board, and will be changed to ensure that the centre of mass is no more than 2cm from the geometric centre of the cube. Each PCB is connected to the others via four main bolts (approximately 2mm diameter and 93mm long) with aluminium spacers and washers that fit between and separate the PCBs. These spacers are either 15 or 25mm long depending on the required space between boards. The boards may be strengthened using Pumpkin mid-plane standoffs.

The area of the ADCS circuitry is assumed to be 25 x 25mm. The mass of the finalised system will be approximately 40g, and will occupy part of a custom electronic board.

Data

Attitude readings will be taken following a nano-meteorite impact, and at specified times during each orbit. The regular readings will give an indication as to the rate of change of the rotation of the cubesat. Readings after the impact will give more accurate directionality data. Each data set will consist of nine readings (three per axis) so that a rotation matrix can be obtained. The data will be time tagged and stored on the SD card until the satellite transmits the data to a ground station. Data will then be processed on the ground. An OBDH document will define the commands sent to the system. Suggested protocols are given below.

Command no. / Time (s) / Command / Pin / Value / Job
1 / -x / Activate ADCS / P1.6 / 1 / Supply ADCS with +5V_SYS power
1 / -x / y / P1.2 / 0 / Report ADCS ready
P1.4 / 0
2 / 0 / Reset / -RTS_MHX / INPUT / Send +5V logic pulse (normally 0)
3 / x / P1.2 / 0 / Select axis x
P1.4 / 1
4 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
5 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
6 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
7 / y / P1.2 / 0 / Select axis y
P1.4 / 0
8 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
9 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
10 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
11 / z / P1.2 / 1 / Select axis z
P1.4 / 0
12 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
13 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
14 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
15 / x / P1.2 / 0 / Select axis x
P1.4 / 1
16 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
17 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
18 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
19 / y / P1.2 / 0 / Select axis y
P1.4 / 0
20 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
21 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
22 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
23 / z / P1.2 / 1 / Select axis z
P1.4 / 0
24 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
25 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
26 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
27 / x / P1.2 / 0 / Select axis x
P1.4 / 1
28 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
29 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
30 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
31 / y / P1.2 / 0 / Select axis y
P1.4 / 0
32 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
33 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
34 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
35 / z / P1.2 / 1 / Select axis z
P1.4 / 0
36 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
37 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
38 / Logic to ADCS / P6.2 / OUTPUT / Read and save analogue voltage
39 / Deactivate ADCS / P1.6 / 0 / Remove +5V_SYS power from ADCS
recover saved data from MCU

Satellite Modes

During sunlight mode the transceiver or camera may be used as it is assumed power from the sun will be sufficient for one or the other of these subsystems, as well as the SD card, MCU, battery charging and the payload. When transmitting the ADCS is off. The payload has priority for writing to the SD card over the ADCS. The ADCS has priority over the camera.

During eclipse the ADCS is active only if the power budget is available. Presently it is believed that ADCS will require minimal power as it is only active periodically at specified times and immediately following payload detection events.

In safe mode the PSU supplies minimal power to save battery life. The payload, SD card, ADCS and camera are turned off.

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