Wiring
The following components are required for an output shift register or LED driver:
- The output shift register or LED driver chip.
- LEDs.
- Assorted resistors.
- 0.1µF capacitors.
Pay close attention to the orientation of the LEDs: the anode (long leg) should be connected to the chip and the cathode (short leg) should be connected to GND. This is the opposite of how LEDs are connected to LED driver chips. The 200Ω resistors are required on every output pin with an LED attached.
Tip
Using a DM13A or other similar LED driver chip is a better choice than using the 74HC595 for driving LEDs.
Tip
To daisy-chain 74HC595 chips, connect the QH' pin (9) from one chip to the SER pin (14) of the next chip. All other control signals, including SRCLK (11) and RCLK (12), must be shared across all chained shift registers.
Pay close attention to the orientation of the LEDs: the anode (long leg) should be connected to +5V and the cathode (short leg) should be connected to the chip. This is the opposite of how LEDs are connected to a 74HC595.
The value of $R_{\text{ext}}$ determines the amount of current for the LEDs. A 5kΩ resistor results in approximately 12mA per LED, a good brightness level for most situations.
Tip
Connecting pin 21, EN , to a PWM pin on a board enables brightness control of the LEDs as a group from MobiFlight.
Tip
To daisy-chain DM13A chips, connect the DAO pin (22) from one chip to the DAI pin (2) of the next chip. Use a dedicated resistor for the REXT pin on each chip. All other control signals, including DCK and LAT, must be shared between all chained shift registers.
Pay close attention to the orientation of the LEDs: the anode (long leg) should be connected to +5V and the cathode (short leg) should be connected to the chip. This is the opposite of how LEDs are connected to a 74HC165.
The value of $R_{\text{ext}}$ determines the amount of current for the LEDs. A 1.6kΩ resistor results in approximately 12mA per LED, a good brightness level for most situations.
Tip
Connecting pin 13, OE (ED2), to a PWM pin on a board enables brightness control of the LEDs as a group from MobiFlight.
Tip
To daisy-chain TLC5917 chips, connect the SDO pin (14) from one chip to the SDI pin (2) of the next chip. Use a dedicated resistor for the R-EXT pin on each chip. All other control signals, including CLK and LE(ED1), must be shared between all chained shift registers.