BillW Just curious if anyone's tried to create a keyboard like percussion controller with a Flex.
Not that I know of, but you may have heard of TouchKeys, which were a very similar technology, with one Trill-like sensor per key.
A Trill sensor takes approx 5 ms for a full scan with the default settings. According to the table here reducing resolution from the default 12 bits down to 9 bits will cut the scan time by more than 3.5 times (the 57/205 ratio), so you can probably get in the neighbourhood of 2 ms per sensor.
When scanning that many sensors, the latency of each individual sensor becomes only one of the factors in determining the overall latency of the system. The time it takes to scan the data from all the sensors becomes critical, too. The I2C bus is limited to 400kHz with these chips and so you may quickly run out of bandwidth on a given bus. Then the host's capability matter: the more I2C busses you have, the more you can parallelise these reads, driving each bus to close to its maximum bandwidth. There's also an EVT pin on each sensor, which you could use to inform the host about touch data being ready to read for that sensor, thus allowing you to selectively read data only from the sensors that do have some data to be read, thus reducing the bandwidth necessary, as you'd only be reading a handful of sensor at a time (only those that are touched). This will require several GPIO inputs into the host board, and you may have to use a wired OR (via diodes) to save GPIO pins.
Also, you may not need each key to have as many sensing channels as there are available on the flex PCB that comes with the stock Trill Flex sensor. You may be better off designing a custom flex PCB which covers 3 or 4 keys, connecting to a single Trill Flex base. This may still give you enough spatial resolution for your purposes while reducing the number of Trill sensors and thus the necessary bandwidth as well as the cost of the whole thing.
The starting point is to put a couple of Trill Flex side by side and see whether they can be activated with your rubber mallets or you are happy to go with a bare skin approach.
Note that the Flex sensors can each be assigned one of a pool of 9 addresses, so you can only have at most 9 of them directly connected to a given I2C bus. If after reducing the number of sensors, you still don't have enough I2C busses and end up needing more than 9 sensors on a given bus, you may have to use an I2C multiplexer. Or get in touch to get a firmware with a custom address range.
