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Wed, 12 Sep 2007
Expansion cards and connectors
One of the challenges with the new Blackfin camera board has been to figure how to best fit it with the existing SRV-1 robot, accommodating the existing 1" x 2" mounting hole pattern for standoffs, fitting a radio module that supports both Zigbee and WiFi 802.11, and supporting the motor drivers, back-emf feedback, and laser pointers.
To make this work, we decided on an approach similar to PC/104 bus which uses stacking connectors for the 32-bit expansion pins, effectively creating a simple 32-pin expansion bus which we may refer to as the "S-32 Bus". The 32-pins are comprised of +3.3V power and ground, 2 UARTs, 2 PWM timers (2nd UART can alternately provide 2 more PWM timers), I2C, SPI with 2 slave selects, and 16 GPIO.
Each expansion board is the same size as the Blackfin camera board - 50mm x 60mm (2.0" x 2.4") and the boards can be stacked in any order. Because of density of components, the Blackfin board doesn't have any mounting holes, but the other boards do have grounded mounting holes in a 1" x 2" pattern to match the SRV-1 base.
Here's a photo which shows how a stack might look -
In this case, we have a board representing the motor controller on the bottom of the sandwich, the processor/camera board in the middle, and the radio board on top. We didn't use the actual Blackfin prototype board in this photo because it has a different connector orientation than we decided upon for the production boards, but hopefully you get the idea. An alternative orientation might put the processor board on top and use a 90-degree extender to orient the camera parallel to the processor - this might be typical for a configuration that just uses the processor/camera and a radio on a UAV.
One other important point - we're publishing schematics for everything, and EAGLE PCB design files for the expansion cards. We have already posted files for the radio board prototype on http://www.surveyor.com/blackfin. We will encourage users to design their own expansion cards, and plan to provide a resource for sharing other designs.
Here is a snapshot of one of the layout files for the radio board which can be downloaded from the Blackfin resource page.
Posted Wed, 12 Sep 2007 14:35 | HTML Link | see additional stories ...