The second “moving message” LED display project I started with was a Cresta AS-0216 (probably) with a defect on the left side of the display.
The characters on the left are filled up in the square block of 5 vertical lines. I got two “keyboards” with the display. So that maybe can become usefull in the future.
Since these kind of displays work with shift registers along the with of the displays, that was the first thing to take a look at.
I opened up the display from the side. The cover and pcb just slides out of the frame.
The system had a green controller board on the left and a brown board with the displays, driver transistors and shift registers.
The shift register used is a CHILONG 3100110005, a 24 bit shiftregister which is unfortunatly made of “unobtainium”. 😉
The bad news was that one of these chips had failed. I swapped the chip most left on the PCB with one one place to the right (installed IC sockets for both). The issue moved up 24 bits to the left, so that’s a win!
This way I was certain that the chip was faulty and that I have to look for a replacement.
A replacement was nowhere to be found, so I thought why not make one myself…
The 24 bit shift register design
I’ve started with using a breadboard and two 74HC595 shift registers in daisy chain setup. But that didn’t work so wel because the 595 uses a latching output that will push the data out on an extra clock pulse, so the data was lagging on clock pulse behind.
Since the 595 wasn’t the right IC to used, I switched over to the 74HC164 shift register, a 8 bit shift register without a latching output:
In the following video you can see it in action as soon as I turn on the power on the breadboard (the flickering of the LEDs is because of the video frame rate)
Two 164’s in series gave 16 bits extra of data! So we need three 164’s in series to replicate the CHILONG.
The schematics and board design
Time for some designing in Eagle CAD…
Because the board uses a 6V power supply, I had to figure out if the system wil work with 5V TTL type shift registers. Luckily the output of the CHILONG chip drives small transistors, so lowering the power rail a bit was not a problem. I simply added a diode in series of the 6v power supply to get to a safe 5.4v for the shift registers.
Also I added a startup reset circuit using a 10k resistor and 100nF capacitor to ground.
Next challenge was to design a board with the size of a 28 dip IC. I’ve came up with this:
After ordering the PCB and all parts, it looked like this:
And the end result…
There was only one challenge to put it all back into the enclosure…
The new shift register PCB in it’s IC socket was to thick, it bumped against the aluminum frame enclosure. So I removed the IC socket, soldered the board directly on the PCB, trimmed a bit from the edge of the PCB and it fitted perfectly in the aluminium case.