Helmut Schmücker
Interface for the encoder of the red fischertechnik motors
Simple Interface for the simple encoder of the red fischertechnik motors.
The interface counts both, rising and falling edges, resulting in 150 counts per revolution. The interface also provides a speed measurement updated with each edge.
Connect the green wire to GND, the red one to +3.3V and the black signal line to any of mbed numbered pins. Additionally connect the signal line via a pullup resitor to +3.3V. A 10K resistor works fine.
Diff: FtEncoder.cpp
- Revision:
- 0:8cb1142a88d5
- Child:
- 1:9e595056c3da
diff -r 000000000000 -r 8cb1142a88d5 FtEncoder.cpp
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/FtEncoder.cpp Thu Mar 14 18:27:24 2013 +0000
@@ -0,0 +1,44 @@
+#include "FtEncoder.h"
+
+FtEncoder::FtEncoder(PinName pwm, unsigned int standStillTimeout)
+ :m_encIRQ(pwm), m_cnt(0), m_standStillTimeout(standStillTimeout), m_cursor(0), m_ready(false)
+{
+ unsigned int tmStmp = getCurrentTimeStamp() - c_nTmStmps * m_standStillTimeout;
+ for(int i=0; i<c_nTmStmps-1; ++i)
+ m_timeStamps[i] = tmStmp + i*m_standStillTimeout;
+ m_cursor = c_nTmStmps-1;
+
+ m_encIRQ.rise(this, &FtEncoder::encoderISR);
+ m_encIRQ.fall(this, &FtEncoder::encoderISR);
+ m_tmOut.attach_us(this, &FtEncoder::encoderISR, m_standStillTimeout);
+}
+
+unsigned int FtEncoder::getLastPeriod() const
+{
+ unsigned int period = 0;
+ unsigned int cursor, cnt;
+ do {
+ cursor = m_cursor;
+ cnt = m_cnt;
+ period = m_timeStamps[m_cursor] - m_timeStamps[(m_cursor-2)&(c_nTmStmps-1)];
+ } while(cursor!=m_cursor || cnt!=m_cnt); // stay in loop until we have an non intrrupted reading
+ return period;
+}
+
+float FtEncoder::getSpeed() const
+{
+ unsigned int period = getLastPeriod();
+ return (period!=0 && period<m_standStillTimeout) ?
+ c_speedFactor/period : 0.0;
+}
+
+void FtEncoder::encoderISR()
+{
+ ++m_cursor;
+ m_cursor &= c_nTmStmps-1;
+ m_timeStamps[m_cursor] = getCurrentTimeStamp();
+ m_tmOut.detach();
+ m_tmOut.attach_us(this, &FtEncoder::encoderISR, m_standStillTimeout);
+ m_callBack.call();
+ ++m_cnt;
+}
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