Page last updated: 21/10/2012
Serial 16 LED Bar-graph
Provide simple LED status indication indication or bar-graph display via a serial port.
Low software / firmware overhead.
Simple design using readily available components.
Low power consumption.
A small and compact design.
Circuit descriptionHere is shown the basic concept in block diagram form for 8 bits of output derived from 3 bits of I/O on the associated microcontroller, to add a further bits of output (as with the final design shown later) at no additional cost in terms of I/O on the microcontrollers part further shift registers are simply cascaded. In practise there are three primary factors limiting how many devices that can be cascaded, increasing drive requirements, increasing capacitance, and software overhead as more devices are added -reducing the possible data transfer rate, thus taking more time to move data between the microcontroller and shift registers.
The 4094 CMOS shift register although capable of driving LED's at modest currents, here we use a buffer between the 4094 shift register and the LED's. The ULN2803 provides this functionality, with each of its eight ports capable of supporting a load current of 500mA (600mA peak) and can withstand at least 50v in the off state. Furthermore the ULN2803 also contains integral suppression diodes for inductive loads although not strictly necessary for driving LED's.
Serial 16 LED Bargraph schematic:
Serial 16 LED Bargraph component placement / layout:
Serial 16 LED Bargraph PCB bottom trace:
Included here are some drivers I wrote for the PIC12F509 microcontroller. Three versions, the original in which both input and output devices were implemented, and two cut down versions one for input devices only and one for output devices only. The original realised 32 bits of input and 32 bits of output from five lines I/O on the microcontroller.
Combined I/O driver CKSIO.ASM
Input only driver CKSIOinput.ASM
Output only driver CKSIOoutput.ASM
Further to the details of the pages above - the original CAD files created using EAGLE PCB Design software are included below, along with associated PDF files of both schematics and PCB layouts suitable for printing directly.
To use the original CAD files, they must be opened with EAGLE. Visit the CADsoft web site for more details, the software (including a freeware version), part libraries, tutorials, for EAGLE are available.
Serial 16 LED Bargraph schematic PDF
Serial 16 LED Bargraph PCB component layout PDF
Serial 16 LED Bargraph PCB bottom track layout PDF
Serial 16 LED Bargraph EAGLE schematic
Serial 16 LED Bargraph EAGLE board