Go Down

Topic: Can somebody give me a bit of help using 4 of the quad alphanumeric displays? (Read 85 times) previous topic - next topic

Wembly

Hey guys, I'm severely new to all of this, and i've been working on a project.

I'm looking at powering 4 of these: http://www.adafruit.com/products/1912 (Backpacks and all) from an arduino Uno r3.

I'm just not hugely sure if thats possible? I'm having trouble figuring out how much power each one of the displays needs, and if it is safe to just power them all from an uno?

I'm also looking at adding 9 of these foot switches to my project too: http://www.aliexpress.com/item/New-Black-Auto-3PDT-9Pin-Stompbox-Guitar-Effects-Pedal-Foot-Switches-True-Bypass-FREE-SHIPPING/32246955677.html

I basically need to be able to receive the signals from the individual foot switches, and be able to enter text to the displays via usb from my laptop.

I'm really sorry about how amateurish this question is, but i've got a deadline, and i'm trying my hardest to not stress out over this.

i've currently got 4 of the displays as i've linked up above, 1 arduino Uno r3, a breadboard and some jumper wires (to begin with, i just need to demonstrate that it's possible to my course leader)


Any help would be great!

ricortes

I'm just not hugely sure if thats possible? I'm having trouble figuring out how much power each one of the displays needs, and if it is safe to just power them all from an uno?

I'm also looking at adding 9 of these foot switches to my project too: http://www.aliexpress.com/item/New-Black-Auto-3PDT-9Pin-Stompbox-Guitar-Effects-Pedal-Foot-Switches-True-Bypass-FREE-SHIPPING/32246955677.html

I basically need to be able to receive the signals from the individual foot switches, and be able to enter text to the displays via usb from my laptop.


I haven't worked with those particular displays but in general you can adjust display brightness by choosing a current limiting resistor setup. Once again, in general each lit segment of a LED display will consume 3-30 mamps. I'm not sure if you are talking 4 of the 2 digit displays or 8 total? That's a lot of juice. You may get away with minimum brightness but if it was me, I would consider using a separate power supply. They say in the product blurb "It's super bright and designed for viewing from distances up to 23 feet (7 meters) away." which kind of indicates to me they can be driven pretty hard. Way too hard for a USB port.

Your design if I have the operation of the effects pedal switches correct will need some software to distinguish transitions. Those switches are latching so if you either need operator to switch the one in use off before they go to a different effect or something in software to switch them. See what I mean? With a latched switch, you could have all 9 on at once or no indication of the switch state. I'm not sure that isn't what you want to do but w/o some indication of state, you can't tell what is whats on and what is off. It could be done using 'pilot' leds on the foot switches, on the Arduino display, in software, or with different switches. Hard to guess how you want them to function.

Paul__B

Well, the answer is - you do not power displays from the Arduino unless you are powering it from USB or a regulated 5V supply.  The USB source will provide half an Amp, but the on-board regulator when powered from the "VIN" or the "barrel" jack can only provide a third of this at best.

So - what is your power source to be?

Wembly

Well, the answer is - you do not power displays from the Arduino unless you are powering it from USB or a regulated 5V supply.  The USB source will provide half an Amp, but the on-board regulator when powered from the "VIN" or the "barrel" jack can only provide a third of this at best.

So - what is your power source to be?

I was hoping to power it over USB. What are my other options?

Paul__B

I suspect that USB will be adequate, but the only way to sort it out is to buy the displays and try it out, measuring the current when you have them (and are actually displaying data).

These displays are of course multiplexed, so the actual current draw is only that of a single digit at any one time.  On the other hand, they are "starburst" alphanumeric displays with twice as many as the usual seven segments.

When you are wiring them up, do make sure you have a 47 µF capacitor across the supply terminals of each (unless that is already incorporated in the module) to even out the current drawn as they perform the multiplexing.

ricortes

I would build or get a 5-12 volt supply for the display and run the Arduino off the USB port since you want to use it to communicate with the Arduino. It would be best to stick a regulator in your display supply for filtering and power line fluctuations. You probably could get away with a wall wart type supply. Sometimes noise finds its way back to other parts of the system so it is possible to glitch the Arduino. Shoot from something in at least the 1 amp range but 2 amp would be better.

If you are are using the i2c interface you already have a common ground from wiring that up. Once again, just to be safe you may want to run another jumper for ground.

Go Up
 


Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

Arduino
via Egeo 16
Torino, 10131
Italy