Connecting 7-segment 2-digit display to TLC5916

Here is project how to use 2x TLC5916 with 7-segment 2-digit LED display.

Board revision 1.0 (initial) is shown on picture.

Project status:

Board was tested successfully. See subproject Connecting TLC5916 to PC using LC 341A USB adapter for example.

Design files

Design files are in revision 1.1, 2019-03-10. New values of R1 and R2 were computed using this setup:

The relation between R_ext and I_led is following (default configuration after power-up):

1. To get I_led in [mA] from R_ext in [kOhm] use:

   I_led = 1.25 * 15 / R_ext = 18.75 / R_ext
   

   For example (used in our circuit now): R_ext = 1 [kOhm] => I_led = 18.75 [mA]

2. To get R_ext in [kOhm] from I_led in [mA] use:

   R_ext = 1.25 * 15 / I_led = 18.75 / I_led
   

   For example: I_led = 20 [mA] => R_ext = 0.937 [kOhm] = 937 [Ohm]

Also see Figure 4. Output Current vs Output Voltage in data sheet to verify that VLED (voltage connected to common LED anode) must be greater than Voltage drop on LED + 1V (roughly). In our case using +5V voltage is OK.

Design was done in Eagle 9.3.0 Free

Schematic is:

Also in:

• PDF version
• Eagle 9.3.0 Free version

PCB design is:

Also in:

• PDF version
• Eagle 9.3.0 Free version

Following Eagle libraries were used:

• zlalanne/eagle-library for definition of TLC5916
• moje.lbr - my own part library (originally for Eagle 3/DOS) made in late 90's in college - used definition of 2-digit HD-A544D LED display

Board was made by gatema.cz for around 700 CZK (roughly 32 USD) including:

• 2 layers
• plated holes
• solder mask
• top silk screen

NOTE: Remember to follow instructions in eagle-dokumentace.pdf from Technicke informace (provided in Czech only)

Bill of Material

• 2x TLC5916 - from tme.eu
• LED display HD-A544D - from gme.cz
• 2x 1K resistor - from my inventory
• 2x 100nF capacitor - from my inventory
• pinhead connector 6 pins in 1 row - used 20-pin DS1021-1x20SF1-10 - from gme.cz

Connecting TLC5916 to Interfaces

There are following subprojects:

• Connecting TLC5916 to PC using LC 341A USB adapter - connecting this board to PC with USB adapter

Known bugs/limitations

Design shortcomings:

• digital signals (CLK, SDI, SDO, LE) should be routed more carefully - not crossing LED lines (where are high current spikes).
• LED display power supply pins (13 and 14) should be wired to +5V supply through jumper pins to allow custom power supply (for example +12V) different from main circuit +5V power supply.