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EFS seems to planning to implement a standard IMU that they use for all projects so they don’t have to remake drivers as often. They have not committed to but the ICM-42688 sounds like it is likely to be the one. It is slightly more expensive than the one above but still super cheap and seems to me much more common, meaning more community support. The features are very similar between both.
During this weekly EE meeting, it was mentioned that EFS would be interested in having a magnetometer/compass as well. They also do not care as much about keeping the IMU in this project the same as the ones they are looking at. The ICM-20948 seems to be the most affordable readily available IMU that contains a magnetometer and it seems to be popular. Also, EFS may be working with the ICM-20948 instead of the ICM-42688 for their standard IMU so this should be a good choice.
Looks like we are changing the IMU again 😭😭😭. Now multiple devices is not necessarily a concern since we have discovered we can put them all on the same bus. We will use the ICM-42688-P since EFS is already using this IMU and it is commonly used for modern drones. It does not have a magnetometer but this will be added separately.
While the placement of the IMU is not critical, it should be placed as close to the center as is convenient. This way rotation will have less of an impact on output acceleration and EFS would have to worry less about factoring the offset into calculations.
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The IMU can communicate with I2C and SPI. I2C and SPI already have ports on the interface board so we could potentially route these to the IMU and use jumper pins so the IMU can be disconnected when this port needs to be used. Unused pins on the STM32 are not connected to the connectors in the ZP3 schematic so these can not be used to to connect to the IMU on the interface board. Using the 61300211121 header pins since we already have the component on Altium.
Edit to the paragraph above. Daniel brought up the fact that I2C and SPI are bussed protocols. Therefore they do not have to be disconnected from the connector and both can be used at the same time. This works fine for I2C but Anthony mentioned that for SPI, we would still need additional chip select lines. We could use the GPIO pins for this. I will still include jumper header pins here so the GPIO pins can be used if desired.
LDO
The VDDIO pin on the IMU has a max voltage rating of 1.95V so a voltage regulator will be needed. I have chosen the AP2112K-1.8TRG1 since it is relatively cheap and highly in stock.
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