Using 2 x 74HC595 to control 2 Seperate LED bars?

Hi there,

I am relatively new to the Atmel/Arduino MCU's and have been playing around with a Mini for a prop I am making.

The basic gist is that I need 2 of the 74HC595 Shift registers (Not chained together) to simultaneously control 8 LED's each (16 Total).

Is their any way to go about this? Or do I need 2 mini's?

that's possible without daisychaining.
You simply have to use 6 Pins (8 with ground and VCC) to control the two led bars

so you have to make two latchpin's, two datapins and twoclockpins.
Know you can shiftoutt both shiftregister how you want

Yes, that's easy and you only need one Mini. Why do you not want to chain the registers together?

There could be a problem, though. 74hc595 was not really designed for driving leds, and cannot achieve maximum brightness for all 8 leds at once. It can drive 3 or 4 leds at max brightness, as long as the others are off, but if all 8 leds are to be on at once, you will have to use a lower brightness to avoid overloading the chip.

There are other chips that are very similar and just as easy to use that don't have that limitation.

Another option which you should consider is using ws2812b leds. These are a little more expensive than ordinary leds, but will save you time and effort overall. Each led has a shift register chip built-in and well let you control colour and brightness of each led individually.

PaulRB:
Yes, that's easy and you only need one Mini. Why do you not want to chain the registers together?

Reason being is that I would like to have 2 separate LED bars in sequence rather than just adding the option for an extra 8 at the end of the first.

I hope I am understanding that right.. :frowning:

I am basically building up the circuitry for a ghostbusters proton pack (With a Blue and Red LED bar graph for the pack and wand respectively)

I'll post a link to what I have done so far with some code that I have found.

oddsoul:
Reason being is that I would like to have 2 separate LED bars in sequence rather than just adding the option for an extra 8 at the end of the first.

Not absolutely sure what you mean. But chaining them would not prevent you from doing any type of pattern you want.

Did you think about my ws2812 suggestion? Nice 'n easy for beginners!

This is what I have going so far. Hope it all makes sense

LED lights

You won't be able to Daisy-chain the leds off a single shift register. The blue leds probably have a forward voltage of about 3.2V and the red ones around 2V, so the 5V output by the shift register won't be enough. You could put the red and blue leds in parallel, but then they would have to share the current, which as I have already said, is limited with the 74hc595, so higher value series resistors will be needed and the brightness of all the leds well be considerably less.

The second shift register won't "waste" any significant amount of power. It will be using a tiny amount. It's the leds that are using almost all the power.

If you are concerned about wasting power and maximizing your battery life, you are looking in completely the wrong place. Right now, 58% of your battery power is being wasted. Its that voltage regulator that is the culprit.

Yeah, Its wasting it in the form of heat. Was the only thing I have to power the circuit at the moment

It would be better to use two separate 4xAA cell holders, wired in parallel. If you use only rechargeable cells, you won't need a regulator, you will get something close enough to 5V to use directly. If you must use that 8xAA holder, get a small dc-dc converter board. That will only waste 10-15% of the power.

Well, you might be re-inventing the wheel by using Arduino to run simple lights in a proton pack. The powercell and cylotron lights can be driven with a 556, 4017, and 2 4015s, as well as a few transistors, and the wand bargraph can also be driven with a 4015 or even a LM3914.

You can run this entire thing from a single 9V without a regulator, depending on the LEDs you use.

Now if you're getting into multiplexing and different sequencing, Arduino is a better idea.

Prop-Forge:
Well, you might be re-inventing the wheel by using Arduino to run simple lights in a proton pack. The powercell and cylotron lights can be driven with a 556, 4017, and 2 4015s, as well as a few transistors, and the wand bargraph can also be driven with a 4015 or even a LM3914.

You can run this entire thing from a single 9V without a regulator, depending on the LEDs you use.

Now if you're getting into multiplexing and different sequencing, Arduino is a better idea.

Im actually using 2 different circuits. I have an LED chaser kit for the Cyclotron lights and the arduino controls the bar LED's.

I have also ripped apart an old car phone charger to use as a 12v-5v converter

oddsoul:
I have also ripped apart an old car phone charger to use as a 12v-5v converter

That may be just a regulator, in which case you will still be wasting most of your battery power.