SAA1064 that refuses to dim...

Its a classic SAA 1064 driving four seven segment LEDs by UNO.

I am using the sketches given in this tutorial to check if the PCB we got made is fine :

My observations: ( The address is 0x70 )

  1. The Counter sketch works fine.
  2. The dimming Sketch does not work.

In fact the main problem itself is that irrespective of any change to the dimming bits ( C4,C5,C6) the intensity remains same in the counter sketch.

I am using BC547 transistors and the timing capacitor is marked 272 which is 2.7nF ( of course I have not actually checked if its the actual value )

Any pointers to check as to why the intensity is not variable ? ( The display module has its direct 5V power supply and not from the UNO)


You have a genuine SAA1064 part?

MarkT: You have a genuine SAA1064 part?

That was a valid point. Never doubted the authenticity of the chip. Let me see ... but I am not sure I will be able to tell if its original by "looks" . Maybe I will order out from another source and try.

Are the BC547 transistors OK for the job ?

Hi. Read this yesterday but got waylaid so just replying now. I may be wrong (I often am), but there appears to a programmatic bug in sketch two, the one that is supposed to test the display brightness. In the initial setup() phase the command byte sent correctly has bit 3 set to switch ‘all segments on’. But this then immediately returns to allow loop() to process, and on each command byte sent during the initXma() calls, where the current setting bits are changed, bit 3 is LOW so the chip reverts to displaying the buffered segment data it holds in its registers - which has presumably been zeroed out.

So you are adjusting the segment current as expected, but just not showing any ‘ON’ digits!

Please do let me know if I am wrong, though. Jim.

Jim, you are bang on target. Yes I noticed it after I posted the query here ( it often is like that - the moment you try to copy code the flaw normally shows up ).

As to me not being able to see the intensity variation, I did realize its happening but not very effective. One reason could be due to the High Intensity LED modules that I am using. Have ordered a set of normal LED modules. Possibly it will show up with them.

Thanks for your post.