tm1637: Support LED modules requiring extra large (100 us) RC time co…

…nstants

tm1637/registers.go

@@ -5,7 +5,19 @@ const (
 	TM1637_CMD2   = 0xC0
 	TM1637_CMD3   = 0x80
 	TM1637_DSP_ON = 0x08
-	TM1637_DELAY  = uint8(10)
+
+	// The black 4-digit and 6-digit TM1637 modules on Amazon and eBay (from
+	// robotdyn.com and diymore.cc) contain a 10nF capacitor with a 10kOhm pullup
+	// registor on each of the DIO and CLK lines. The RC time constant is 100
+	// microseconds, which forces the bit transition delay to be somewhere in
+	// the 100 microsecond range.
+	//
+	// The blue 4-digit TM1637 modules contain a much lower capacitor (220 or 470
+	// picofareds?), so the bit transition delay can be as low as 3-5
+	// microseconds.
+	//
+	// TODO: This should be an adjustable parameter.
+	TM1637_DELAY  = uint8(100)
 )
 
 // 7-segment characters encoding for 0-9, A-Z, a-z, blank, dash, star

tm1637/tm1637.go

@@ -164,6 +164,7 @@ func (d *Device) start() {
 	pinMode(d.dio, false)
 	delaytm()
 	pinMode(d.clk, false)
+	delaytm()
 }
 
 func (d *Device) stop() {
@@ -172,6 +173,7 @@ func (d *Device) stop() {
 	pinMode(d.clk, true)
 	delaytm()
 	pinMode(d.dio, true)
+	delaytm()
 }
 
 func (d *Device) writeByte(data uint8) {
@@ -188,6 +190,7 @@ func (d *Device) writeByte(data uint8) {
 	pinMode(d.clk, true)
 	delaytm()
 	pinMode(d.clk, false)
+	delaytm()
 }
 
 func (d *Device) writeCmd() {