Display HT16K33 6 digit 14 segments 0.54"



I wanted some displays slight different that the ebay/aliexpress offering and decided to design my own.
The idea with this design is that my LED display driver library supports this schematic. This means that in addition to the boards designed here, the schematic can also be included in other projects (With or without indicators and buttons) and then the library will support the display for that design.

Contents
    Display HT16K33 6 digit 14 segments 0.54"
    Requirements
    Design
        Parts to use
        Schematic
        Part list
        Using the button input
        Circuit board
            Mounting
        Options
    Conclusion
    Notes and download

Requirements

• PCB must be cheap to produce, i.e. not larger than 10x10cm.
• The board is for 14 segments displays.
• Include inputs for a couple of buttons.
• Indicator above each digit.
• Must be able to mount edge to edge for longer displays.
• Circuit board must have mounting holes that can be used for either front or back mounting.

Design
Parts to use

For the digits I selected dual 14 segment 0.54" alphanumeric displays, I can have 3 of these within 10cm (Nearly 4, but that would be slightly to long). For indicators I decided to use a 5mm RGB led for each digit, this is a very flexible solution.
The above means I have 6x15 leds for the displays and 6x3 leds for the indicators for a total of 108 leds to drive.

The displays I uses are from KingBright:

• PDC54-11: 13.8mm/0.54" 14 segment dual digit alphanumeric display, 15 bit version
• PDC54-12: 13.8mm/0.54" 14 segment dual digit alphanumeric display, 8 bit version

The two different displays.






This is the 8 bit version where some pins are missing.






And here the 15 bit version.



To search for other compatible brands, check the pins are placed this way (Pin 1 is bottom left) and that the display is common cathode. This is the same information as the two drawings above shows, but because other brands use other letters for segments it is easier to use this drawing for matching segments.

For driving LED displays the typical chips are:

• HC595: Fine for static driving, but needs a chip for each 8 leds and resistors for each segment, can be chained together.
• MAX7219: Can multiplex 8x8 (64) common cathode leds and be chained together.
• TM1637: Can multiplex 6x8 (48) common anode leds and support key input.
• TM1638: Can multiplex 8x10 (80) common cathode leds and support key input.
• HT16K33 20pin: Can multiplex 8x8 (64) common cathode leds and support key input.
• HT16K33 24pin: Can multiplex 8x12 (96) common cathode leds and support key input, chip is addressable and allows 4 chips on the same connection.
• HT16K33 28pin: Can multiplex 8x16 (128) common cathode leds and support key input, chip is addressable and allows 8 chips on the same connection.

For the above number of displays and indicators the HT16K33 28 pin is the obvious chip to use and it is fairly cheap.

The indicator is a standard common cathode 5mm RGB led:






Schematic

Before starting on the schematic I ordered some displays and when starting on the schematic I found out that they had a 8 bit interface, not the expected 15 bit interface. I decided to do two versions, one for 8 and one for 15 bit displays (The extra PCB was only a few $).
The 8 bit display could be used with a MAX7219 driver, but I am using a 16 bit wide driver that can also be used for the 15 bit display.



Displays with 8 bit interface.



Displays with 15 bit interface.

A important point for me was to keep the amount of soldering (especially SMD) as low as possible, i.e. only include what is absolute necessary for the circuit. That affect how I designed the button interface.
Because the chip uses the same matrix for buttons as for display, pressing two buttons will short two segments, this do not in any way damage the chip or display, but it looks silly. To avoid this each button can include a series diode, I did not make space for them on the circuit board. They can be mounted at the buttons if desired.

This design is for 5V and is not guaranteed to work when connected to 3.3V processors, a level translator must be included between the display and the processor.



The memory map of the HT16K33 controller for the 8 bit version, it is a bit convoluted.
The red part uses the segment definition from my library (As shown beside the table), the . is short for DP and the _ means a unused bit.



The memory map for the 15 bit is much easier to work with.



Part list

Reference	Number of	Component
U1, U2, U3	6	KingBright PDC54-11 any color or similar (pinout is fairly standard) (15 bit version)
U1, U2, U3	6	KingBright PDC54-12 any color or similar (8 bit version)
D1, D2, D3, D4, D5, D6	6	RGB 5mm led, single color 3 or 5 mm led can be used
U4	1	HT16K33 28 pin
R1, R2, R3, R4, R5	5	22kohm 0805
C1	1	100nF 0805
C2	1	47uF 1206 (Smaller capacity can be used)
D7	1	1N4148 diode SOD323 or other small diode.
J1	1	9 pin strip
J2, J3	2	4 pin strip

The price is controlled by two items: The displays (About $2 each) and shipping, everything else is about $2 together. It is necessary to buy for multiple PCBs to get this price (i.e. 10 displays, 5 pcbs and 10-100 each of the passive parts and the diodes).
I got the displays from mouser.com and the HT16K33 from lcsc.com (It is also on aliexpress.com).
The other parts are from aliexpress.com, ebay.com and lcsc.com



Using the button input



The button switches can be wires with or without diodes:

• No diodes: Pressing a button will turn a segment off
• One diode: Pressing two or more buttons may light wrong segments
• 8 diodes: Display is not affected by button presses.

The chip supports up to 39 buttons using 3 scan lines and 13 input lines. If more than 8 buttons are needed it is possible to find the signals on the back of the PCB on the display pins. The library reads all buttons inputs, but do not return more than the first 8, to get more the code must be modified.



Circuit board




The 8 bit layout with 3 digits, 6 leds, a connector for 8 buttons and two data connections one on each end of the circuit board.




The 15 bit layout reused the placement of all nearly parts, but the tracks are connected very differently.





The board size and placement of mounting holes is exactly the same between the  boards. The mounting holes is for M2 screws.




The 8 bit PCB back from production. I selected a black finish, to get a dark background for the leds.




And the 15 bit version.
There is one minor error on both, the symbol for D7 is the wrong way around!


Mounting

For easiest mounting use this sequence:

• SMD parts including chip HT16K33
• The 3 pin strips.
• The displays
• The Leds. The easiest way to mount them is to solder one pin, cut all the pins and then solder the rest.

The chip has a marking at pin 1 and must be mounted in the orientation shown above (The white line indicates pin 1).



Diodes has a line to mark direction, this line must be mounted towards the resistors.





Orientation of display, only the right version works, i.e. -11 in 15bit PCBs and -12 in 8 bit PCBs



The long pin of 4 pins RGB leds goes in the marked hole. With single color leds it is the short pin that goes into the marked hole and the long pin goes in the 4 hole, this means they will be on the blue indicator line.







The two boards mounted.



Two 15 bit boards in series.



To use multiple boards the correct address links must be shorted:

• First board (Digit 0 - 5): All must be open
• Second board (Digit (6 - 11): Short A0
• 3. board (Digit 12 - 17): Short A1
• 4. board (Digit 18 - 23): Short A0 and A1
• 5. board (Digit 24 - 29): Short A2
• 6. board (Digit 30 - 35): Short A2 and A0
• 7. board (Digit 36 - 41): Short A2 and A1
• 8. board (Digit 42 - 47): Short A2, A1 and A0

Options

All parts can be mounted on the PCB, but it may not be necessary.

• Indicators need only to be mounted if they are going to be used.
• It is possible to use a single color 3 or 5mm leds instead of the RGB led for indicators.
• Button input connector need only be mounted if any buttons are going to be used.
• Not all digits may be needed, only U1 or U1+U2 can be mounted for 2 or 4 digit versions.
• The address selection (R1, R2, R3, D7) is only necessary to mount if multiple display must be used on the same two communications wires.
• Same goes for the two 4 pin connectors, only one is needed, the second is for easy connection to other displays.
• If the communication wires already have pullup at some other location, the two pullup resistors (R4, R5) are not necessary.

This means the simplest version is only HT16K33, two capacitors, one 4 pin connector and 1 to 3 displays.

The 5mm leds are about 0.5mm higher than the display, this means to mount the display flush against some window the leds must either be sanded down or the displays must be mounted slightly above the circuit board.



Conclusion

I like this design (Probably because I did it myself) and with both multicolor indicators and button input it can save some pins on a Arduino. The 14 segments means I can show words, but it looks nicest for upper case letters, lower case is not rendered as good.
The possibility to link displays and mount them edge to edge means I can make any size divisible with 2 from 2 digits to 48 digits. With the dual IO connectors wiring is fairly easy.

I will not be selling this board, but you can order the raw board yourself from any PCB manufacturer by using the gerber files and then you will have to mount the parts. It is also possible to use the schematic as part of other projects, this will mean my display library will work directly.



Notes and download

Gerber for 8 bit display
KiCad project for 8 bit display

Gerber for 15 bit display
KiCad project for 15 bit display

LED display driver library