Hi there;
I'm building a large 7 segment display (as in a few feet across). It's not animated or anything, just a simple clock/scoreboard. 6 digits, viewable at 75' is the requirement.
I've reduced it to its simplest component, which would appear to me to be a frame with iosolated c7 bulbs (ie christmas lights) blocked and diffused appropriately into segments.
So I need to control ~50 lights, individually. Something similar to: 4 Watt - C7 - Clear - Candelabra Base 3,000 Life Hours - 16 Lumens - 120 Volt - PLT
I'll obviously need external power. And I'm fine devoting an ardino mega to this, and using basically all of its pins. But can I safely use transistors to ramp me up to the driving power for each, or need I get relays? Or is there another option I'm missing? Cost-effective but safe is the name of the game here.
Any help is appreciated.
I'm assuming the 120V is coming from the mains? If I was doing something like that, I might be tempted to use small transistors switching triacs. I might also think about opto-isolating everything, just in case.
Personally id include a power supply and use leds for simplicity, and then your working with safer voltages, less heat, no need for replacing lights either if you take care of the leds
then some transistors or mosfets to switch them, either a whole bunch of little leds or some high power ones
either a whole bunch of little leds or some high power ones
I really don't want to wire thousands of leds. And working with matrices just increases the cost and doesn't give me any benefit (I don't need scrolling or animation or anything of that type).
On balance (cost, safety, reliability etc) I'd suggest you go for 6 off 8-way relay boards. You need 7 switches per numeral so the 8-way boards fit the bill and give you one spare relay should you need a decimal point. These are available off-the-shelf from arduino system suppliers and suitably rated and designed for switching mains voltages
I'd suggest you go for 6 off 8-way relay boards
Thanks. I'd seen these and they crossed my mind.
6 at $20/per adds up though, especially as I'm going to need a 2 lane system (so $240 + lights + wires + frame.... ugh). Given that normal people run a string of lights rather than just 1 light, I assume that just 1 or 2 8blocks could easily power the whole chain. Is there a way for me to wire it to have the m still properly powered, but individually controllable, without the necessity of using 42 separate relays? Apologies, I'm a software geek, and just learning the hardware side of things.
I'm not sure there is a "cheaper" way that would be suitably reliable. However you might want to consider the following :-
There maybe the possibility you could "strobe" each of the 6 numerals in turn for which you'll need 6 SSRs. (relays cannot be strobed at high speed) Each SSR permits power to the relevant numeral when it is to be considered "active"
Then you would need 7 SSRs to drive each segment of the numeral array (again relays would be unsuitable) All similar numeral segments can be driven by a single common source since it is the previously mentioned "strobe" SSR which determines which numeral is illuminated.
So, a total of 13 SSRs and a whole lot of software to perform the strobing.
Assuming each numeral is strobed in turn that means a maximum turn-on duty time of only 16.6% of a complete strobe cycle. You will/may need a little space between each strobe to achieve the switching so perhaps a maximum of say 15% duty cycle. At such a low duty cycle you may experience flicker.
Given a choice I'd go for the simpler but more expensive relay system.
Alternatively you might want to use a "flip-flag" concept as used on railway and airport notice boards, whereby bright white letter segments are made visible as required. These could be strobed and latched as required using only 13 relays. If you need them "bright" then make them reflective and shine fixed bright lights onto them.
I've made a similar project using led modules (a waterproof enclosure that contains 5 piranha leds) based on this webpage: 12ft GPS Wall Clock - SparkFun Electronics
You just need some UNL2003 to drive the led modules.
At the price of relays and the cheapness of leds and transistors id say that's your best price, setup a little data bus running down the boards with maybe i2c I/o expanders driving transistors/mosfets powering some leds
42 transistors and say (42 high power leds or 420 regular leds) will be pretty cheap
You could use a board like this, basically a promini with u to 12 TPIC6B595 shift registers, to drive 12V LED strips. Very bright, make you display any size you want.
I offer bare boards for $5.00 mailed to your US location.
Or I can sell populated for more.
Here's a clip of 4 digits being driven as a test (turning off each segment individually)
led_strip_test.MOV (667 KB)
Here are some letters scrolling across 4 digits, with 8th segment added to expand letter capability.
I have a 4.3V .mov of this seen across a hall, little too big to post here.
words1.MOV (1.98 MB)
