@@ -30,31 +30,6 @@ need a larger SAMPLE_COUNT for reliability. | |||
Larger SAMPLE_COUNTs are more reliable but consume more memory, where | |||
SAMPLE_COUNT*ROW_COUNT = bytes of memory consumed by keyboard | |||
SAMPLE_COUNT = 4 is very reliable for a keyboard. | |||
Avoid sampling the switch input at a rate synchronous to events in the environment | |||
that might create periodic EMI. For instance, 50 and 60 Hz. | |||
A keyboard with a faster scan rate responds faster. | |||
Follow these step to tune DELAY_MICROSECONDS for maximum scan rate for a given SAMPLE_COUNT: | |||
Initialize DELAY_MICROSECONDS in your sketch: | |||
const unsigned int Row::DELAY_MICROSECONDS = 1000; | |||
Add this to the sketch's loop() function: | |||
debug.print_microseconds_per_scan(); | |||
Compile and load the sketch into the microcontroller; microseconds_per_scan is printed every second. | |||
Adjust the value of DELAY_MICROSECONDS and repeat until: | |||
debug.print_microseconds_per_scan() <= DEBOUNCE_TIME / SAMPLE_COUNT | |||
DEBOUNCE_TIME can be obtained from the switch's datasheet. Some switch bounce times are: | |||
Cherry MX specifies 5msec bounce time http://www.cherrycorp.com/english/switches/key/mx.htm | |||
hasu measured Cherry MX bounce times .3ms to 1.4ms http://geekhack.org/index.php?topic=42385.0 | |||
Tactile switch MJTP series bounce 10 ms http://www.apem.com/files/apem/brochures/MJTP_6MM.pdf | |||
Polling I2C may slow the scan rate enough so that no additional delay is needed: | |||
const unsigned int Row::DELAY_MICROSECONDS = 0; | |||
Slow-scan trick for debug messages that print too fast: | |||
change DELAY_MICROSECONDS to a large number like 10000 | |||
That way debug messages are printed at a managable rate. | |||
*/ | |||
/* debounce() function | |||
Parameter rowState is bitwise, 1 means pressed, 0 means released. |
@@ -33,7 +33,6 @@ Number of ColPort::colPins should equal number of keys in Row::ptrsKeys array | |||
class Row : public RowBase | |||
{ | |||
private: | |||
static const unsigned int DELAY_MICROSECONDS; //delay between each Row scan for debouncing | |||
uint8_t samples[SAMPLE_COUNT]; //bitwise, one bit per key, most recent readings | |||
uint8_t samplesIndex; //samples[] current write index | |||
virtual uint8_t debounce(const uint8_t rowState); |
@@ -9,12 +9,44 @@ void RowBase::process(const bool activeHigh) | |||
uint16_t rowEnd; //1 bit marks positioned after last key of row | |||
uint8_t debouncedChanged; //1 means debounced changed | |||
wait(); | |||
scan(activeHigh); //save column-port-pin values to portState | |||
rowState = getRowState(rowEnd, activeHigh); | |||
debouncedChanged = debounce(rowState); | |||
pressRelease(rowEnd, debouncedChanged); | |||
} | |||
/* wait() delay's scan to give switches time to debounce. | |||
This version of wait() is very simple. More sophisticated versions can override this one. | |||
For fastest response time, wait() should be placed before scan() or after pressRelease() | |||
(waiting between strobe and send would unnecessarily delay send). | |||
A keyboard with a faster scan rate responds faster. | |||
Follow these step to tune DELAY_MICROSECONDS for maximum scan rate for a given SAMPLE_COUNT: | |||
Initialize DELAY_MICROSECONDS in your sketch: | |||
const unsigned int Row::DELAY_MICROSECONDS = 1000; | |||
Add this to the sketch's loop() function: | |||
debug.print_microseconds_per_scan(); | |||
Compile and load the sketch into the microcontroller; microseconds_per_scan is printed every second. | |||
Adjust the value of DELAY_MICROSECONDS and repeat until: | |||
debug.print_microseconds_per_scan() <= DEBOUNCE_TIME / SAMPLE_COUNT | |||
DEBOUNCE_TIME can be obtained from the switch's datasheet. Some switch bounce times are: | |||
Cherry MX specifies 5msec bounce time http://www.cherrycorp.com/english/switches/key/mx.htm | |||
hasu measured Cherry MX bounce times .3ms to 1.4ms http://geekhack.org/index.php?topic=42385.0 | |||
Tactile switch MJTP series bounce 10 ms http://www.apem.com/files/apem/brochures/MJTP_6MM.pdf | |||
Avoid sampling the switch input at a rate synchronous to events in the environment | |||
that might create periodic EMI. For instance, 50 and 60 Hz. | |||
Polling I2C may slow the scan rate enough so that no additional delay is needed: | |||
const unsigned int Row::DELAY_MICROSECONDS = 0; | |||
Slow-scan trick for debug messages that print too fast: | |||
change DELAY_MICROSECONDS to a large number like 10000 | |||
That way debug messages are printed at a managable rate. | |||
*/ | |||
void RowBase::wait() | |||
{ | |||
delayMicroseconds(DELAY_MICROSECONDS); //delay between Row scans to debounce switches |
@@ -11,6 +11,7 @@ | |||
class RowBase | |||
{ | |||
private: | |||
static const unsigned int DELAY_MICROSECONDS; //delay between each Row scan for debouncing | |||
Key *const *const ptrsKeys; //array of Key pointers | |||
RowPort &refRowPort; //this row's IC port | |||
@@ -19,6 +20,7 @@ class RowBase | |||
ColPort *const *const ptrsColPorts; //array of column ports | |||
const uint8_t colPortCount; | |||
void wait(); | |||
void scan(const bool activeHigh); | |||
uint8_t getRowState(uint16_t& rowEnd, const bool activeHigh); | |||
virtual uint8_t debounce(const uint8_t rowState)=0; |