SAA1064 Display controller @12V

Other Hardware General Electronics
1

I have connected a Mega to a SAA1064 and all is well with red displays.

I am using large size display modules ( 25mm height) and have a problem with the Green Variety. Its a KingBright model SA10-21C6KWA. Even working with 5V and max brightness ( bits 4,5,6 ON) I still don't get it bright enough. In fact i can barely see it.

Increasing the voltage from 5 to even 5.2V of course improves the situation . However i cant do this as the UNO will get fried.

I hence tried to have two power supplies - one 5V for the UNO and another 12V for the SAA1064 board ( it can go upto 15V as per data sheet)

Sadly the display is dead when i try as above. I even tried to connect the GND or 0V of both power supplies. No luck.

How does one go about this ??

2

Hi,
Check the forward volt drop of the red and green LEDs.

The SAA1064 may have to be reprogrammed for higher volt drop that the green LED possibly is.

Tom.... :slight_smile:

3

Those displays have two LEDs in series per segment, and might need >6.5volt to work.

Had a quick look at the datasheet of the SAA1064. VCC can be up to 15volt.
Can't you use a 9volt supply for the chip.

5volt I2C (pull up to the Arduino 5volt pin) should still be possible.
The datasheet even states an absolute Vmax on the I2C lines of 5.9volt.
Leo..

4

@Tom

You are right. The Green module needs a forward voltage of 4.15V to push 10mA through each segment and the Red module needs about 3.2V. So that pretty much sums up the issue. Thanks.

@Wawa

This SAA1064 chip is intended to be used with MCU generally. But has been designed with a maximum voltage of 15V - obviously they allow the user to connect the collectors of both drive transistors to a higher voltage and run the SAA1064 chip itself @5V from the same MCU power supply. This also will ensure that the I2C pins run at the 5V logic, just by tying two 4.7K resistors to the SDA and SCL lines. Possibly this should work ?

5

I understand that the chip typically is used on a 5volt supply, but can go as high as 15volt (chip and drivers).
But that the I2C lines must be used on <= 5volt.

The Arduino can supply that through it's pullup resistors (a Mega has onboard 10k pull up resistors to 5volt).
I2C is basically open collector/drain switches to ground.
Leo..