Using two Octo D type flip flops SN74HC377N to run LED's

Hello,

I have an old DMX controller board that I am butchering and plan to wire in to an Arduino Mega. There is a bank of LED’s running off two SN74HC377N that I have spent all day trying to figure out how the circuit works and was wondering if anyone has any suggestions?

I’ve confirmed there is 5 vdc available to the transistors. I have tried putting one of D on U10 and to U12 in various combinations to high and clocking but nothing seems to happen.

Schematics attached.

Any thoughts would be greatly appreciated.

Did you have a common ground?
Did you use the active low clock enable?

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Nothing seems to happen.

What does this mean exactly? I mean, I guess the LEDs don't light but more specifically, for example, have you put an oscilloscope on the outputs to see if they change?

What are you feeding into the enable pin, pin 1? Pin 1 need to be held low for anything to happen.

As lighting the LEDs requires co-ordination between the 2 shift registers it matters what is on the D inputs. U10 (for the LEDs) should have the D inputs high and and U12 low for any LEDs to light.

And ground.

Thanks for the replies so far.

Yes there is a common ground. And I have tried taking clk and enable low.

PerryBebbington:
What does this mean exactly? I mean, I guess the LEDs don't light but more specifically, for example, have you put an oscilloscope on the outputs to see if they change?

What are you feeding into the enable pin, pin 1? Pin 1 need to be held low for anything to happen.

As lighting the LEDs requires co-ordination between the 2 shift registers it matters what is on the D inputs. U10 (for the LEDs) should have the D inputs high and and U12 low for any LEDs to light.

And ground.

Yes I mean I cannot get the LED's to light up. Unfortunately I do not have an oscilloscope, but the LED's do flash momentarily when the power is first applied.

I am confused by how to connect D on U10 high and U12 low as they pin go to pin 3 on their respective chips which a physically connected together - P00, when I tried the board shorted out.

I am confused by how to connect D on U10 high and U12 low as they pin go to pin 3 on their respective chips which a physically connected together

OK, sorry, I missed that bit. You can’t. What you can do is set P00 high and clock U10 then set it low and clock U12. Don’t forget that while clocking pin 1 should be low on the shift register you are clocking.

Have you read the data sheet?

PerryBebbington:
OK, sorry, I missed that bit. You can't. What you can do is set P00 high and clock U10 then set it low and clock U12. Don't forget that while clocking pin 1 should be low on the shift register you are clocking.

Have you read the data sheet?

Many thanks for your help, I really appreciate it.

I have tried clocking U10 High and then U12 Low, I get varying weird results. However I've noticed that both clk on pins 11 are both coupled together at WR. Only pins 1 on both U10 and U12 are not connected together.

I have read the data sheet an pin 1 is listed as clock enable where as the schematic shows it as just enable - I assume there are the same thing?

pureliquid:
I have read the data sheet an pin 1 is listed as clock enable where as the schematic shows it as just enable - I assume there are the same thing?

Yes. I would interpret it this way: the last two characters of the signal name on the enable pins, CS, stand for Chip Select. Present the data on P00-P03(07) ,set CS low on the 377 you're writing to and clock /WR. When done, set CS back to high.

I have tried clocking U10 High and then U12 Low, I get varying weird results. However I've noticed that both clk on pins 11 are both coupled together at WR. Only pins 1 on both U10 and U12 are not connected together.

OK, that makes sense. In that case you control which register gets clocked by setting pin 1 low on the one you want to clock and high on the one you don't want to clock. Note that it is not enough to not connect pin 1, you must connect it to 0V or 5V, do not leave it floating.

I get varying weird results

What do you get? Have you lit some LEDs yet, even if not the ones you hoped for or expected?

PerryBebbington:
Have you lit some LEDs yet, even if not the ones you hoped for or expected?

Sorry it was late last night and realised I hadn't connected a few pins correctly and had am error iny code. Everything is now working as expected- so thank you very much for your help.

I will now try and figure out how to incorporate the buttons in as well.

pureliquid:
Sorry it was late last night and realised I hadn't connected a few pins correctly and had am error in my code.

We all do that! An impossible problem when you are tired becomes easy after a good night's sleep.

Everything is now working as expected- so thank you very much for your help.

Good! You are welcome! :slight_smile:

I will now try and figure out how to incorporate the buttons in as well.

Should be a lot easier now you know how to drive the shift registers.