There are at least two types of TM1637 LED modules which seem to be readily available on Amazon and eBay currently.
- One type is labeled as being manufactured by diymore.cc and is available is 5 different colors (white, red, yellow, green, and blue). They manufactured on black printed circuit board, and come in 4-digit and 6-digit variations.
- Another type is a 4-digit a blue printed circuit board, but does not have any labels on it.
The LED modules from diymore.cc come with a 1 uF smoothing capacitor and a 0.1
uF filter capacitor across the VCC and GND lines. In addition, there are 2
noise rejection capacitors on the DIO and CLK pins to ground, as shown in
the schematic below:
The capacitors for CLK and DIO lines are 10 nF, which is about 50-100X
larger than they should be. It causes the RC time constant to be about 100
microseconds, which forces the delayMicros parameter in
SimpleTmi1637Interface and the DELAY_MICROS parameter in
SimpleTmi1637FastInterface to be 100 microseconds. According to the TM1637
datasheet, the controller chip has a maximum clock frequency of 500 kHz (50%
duty cycle), which implies a theoretical DELAY_MICROS of 1 microsecond.
The actual minimum value for the delayMicroseconds() function might be as low
as 0 for several reasons:
- there is overhead in calling the
delayMicroseconds()function - the implementation of the
delayMicroseconds()function on AVR processors is not accurate for small (less than 10) microseconds - there is overhead for the
digitalWrite()ordigitalWriteFast()functions - there is overhead in the bit-shifting and looping
If you are handy with a soldering iron, you can remove the two 10 nF capacitors.
The capacitors are located in different places depending on the size of the LED
segments and the number of LED segments. The best way to identify the correct
capacitors is to use a multimeter and find the capacitors where one end of the
capacitor is connected to GND and the other end of the capacitor is connected
to either the DIO pin or the CLK pin.
In theory, these capacitors should be replaced with ones in the range of 100 to
500 pF , to prevent interference from high frequency noise on the CLK and
DIO lines. However, I have tested these modules with no capacitors on the
DIO and CLK lines, and was able to use a delayMicros or DELAY_MICROS as
low as 1 microsecond.
Here are the photos of the LED modules that I modified, where the red box marks the place where the capacitors were removed:
