saving you costs: 4-digit LED display drive using 16f54
 

Over the past 5 years I have seen many different ways to drive LED displays.
And I tried some designs myself.

One solution is to use a small microcontroller only for the display,
and clock in data serially!

The 16f54 as TSSOP is a very small IC. And it costs less than the display itself.
No extra parts are needed indeed except for the clock signal generation.
I use a coil here while also a resonator or crystal could be used.

So extra parts count is just one part, plus one resistor but that is not strictly needed.

I share the source code so you can advance too!

However:

1. No ownership or copyright is transfered.
2. The code to read external serial data is not implemented.
You would have to add it yourself.
3. Since it's a small controller with 512 words FLASH, assembly language is used.

Many electronics gadgets these days have a short live cycle just a few years.
After that they end up as e-waste.
There is no need to bury parts which are not absolutely needed.
There is no need to use technology from 10 or 20 years ago.
It's perfectly possible to use SMD "at home".

By the way you could copy and paste the source directly from the PDF for instance using foxit reader.

I don't like this design , the LEDs will be damaged pretty soon when we can't control the current passed them.

And what. Most cheap electronics gadgets have a lifetime of 1 to 3 years.

The current is controlled:

-Internal LED resistance
-2X MOSFET junctions (drive and sink)
-8 phase multiplex
-Low voltage for instance 3.0 volts

Thank you for your opinion I value it as well I value any kind of response.

However I second this opinion see photo: (attached).

It is true yes the "1" is a bit more bright than the others.
But this well could be compensated in software!

It is hard indeed to burn a LED using a button cell.
I use them to test LEDs before soldering.

When I write 1 to 3 years lifetime, it is based on own experience I had with gadgets. Maybe 50 of them. Sometimes wires or buttons break just after a few months. Even for expensive digital camera. The battery door broke after a few weeks.

One LED matrix circuit works for more than one year now. Same drive system, directly by the PIC ports, no resistors, 2.4 volts batteries. There is not any sign of LED damage.

Evolution...

Over the years I tried various methods to drive LED dispplays.

Including:

-resistors in the drive path, and to use a transistor + base resistor for the sink
-using 74hc595 and also 74hc164 serial buffers, without resistors in the drive path
-using digital MOSFET for the sink drive (no gate resistor)
-LCX 244 (74hc255) octal buffer for the sink
-direct PIC drive as you see here

For instance I use LED display for a RAM bootloader module (attachment).
It is built from 2x 74hc595 and 1x lcx244, no resistors, but still quite an effort to wire.
Why have all these extra wires, space, and chips, when they are not needed?

I think the display will at least last a few years. Maybe the lifetime expectation will not be affected at all.

However, such a prototype circuit, with a LED display for debugging, will not be used 24 hours over years. It will be used for some hours during the prototype phase.

When I build prototypes, I try many ideas, when there is improvement, and it is relieable over time, I also use it for future circuits.

I had the circuit running for a while and overheating/burnout wasn't an issue at all.

Then I made PCBs actually.

I searched the net many people actually use big circuits for 7segment drive, even if they use multiplex they still use transistors+resitors, quite an effort.

http://farm8.staticflickr.com/7014/6...c98871fe_m.jpg
7segment patterns by tetsu-jp * has new modem, on Flickr

the patterns to drive the display, avoiding I/O remapping. Not all pins can be used freely, the ICSP pins only can be used for cathodes sink. If there is "High" potential, it will be blocked by the 7segment LED!

http://farm8.staticflickr.com/7002/6...3131a20e_m.jpg
serial communications circuit by tetsu-jp * has new modem, on Flickr

Test PCB for serial communcations, 2x PIC 16f54

http://farm8.staticflickr.com/7147/6...ca36f69d_m.jpg
2 microcontrollers system by tetsu-jp * has new modem, on Flickr

Using a GAL programmer module for the 2nd PIC

The code for the 16f54 is a bit exotic since a ready signal must be polled, and data can only be sent during blank phases (8 phase drive every second phase is blank).
To sell this PCB a PIC with hardware serial port would be better, since it is more complicated to use software-based serial communications.

It is interesting to search the net and to come accross many circuits which have amateur/hobbist level, many of them use very old PIC models, for instance 16f84 or 16f8xx.

I do not see it very often that people actually look at their circuit, then rebuild it again even 3 or 4 times to improve the design.

demonstration video here.

3x 16f54 - 1 master, 2 displays.

http://pic.hitechworld.org/16f54pcb.html

I want to use the display for instance:
http://www.flickr.com/photos/takao21203/6988661837/

radiation counter, powered by 2.4 volts.

If you are interested in any of these displays, price is only $6.