new user project question — Parallax Forums

# new user project question

Posts: 9
In the enclosed file, my project will use 4, 8x8 matrix. Two white and one red and one green. This is an "extension" signal light controlled from another source and no more than 2 lights will be on at the same time. For discussion purposes, the time any light will be on, is momentary. The source does not have enough power, hence the separated power source.
My questions are:
#1. Is a 12volt external power source [batteries] enough to power commonly available 8x8 matrixes {x2} ? Or would a 9 volt battery be suficient?
#2. Should resistors be used downstream of the matrixes? If so, what value?
#3. The unit will be 25 feet away from the controller - is there a concern about power loss using 24 gauge wire for that distance? Or is a larger gauge a better choice?
#4. What changes would need to be added to my diagram, to add a buzzer or possibly separate sounds for the white and colored LED's?

• Posts: 1,268
What type of Lamps are you using. This makes a difference as to the current draw.

Are they the ones that have a sticky back on them like a rope?

Mike
• Posts: 8,697
edited 2021-01-21 18:30
Your diagram shows the led matrix as a single lamp, but the matrix leds are an array of 64 leds connected in 8 rows x 8 columns. If you want to use the matrix as a single lamp you will need a current limiting resistors on each of the rows or columns. Assuming the resistors are connected to the rows you will connect the +V to all the resistors and -V to all the columns.

The resistor values will depend on the forward voltage of the matrix leds, the power supply voltage, and the desired current level. Typical led forward voltages range from about 1.5V to 4V depending on the color, so even 6V would be enough to drive the leds. With all those leds connected in parallel (64 x 4) it will have a fairly high current draw so #24 wire may not be enough unless you use a higher voltage (~12-24V) and a switching regulator near the leds to provide 6 volts or so to the matrix leds.
• Posts: 10,543
commonly available 8x8 matrixes

There are lots of different 8x8 matrixes. Some are common anode some are common cathode. Some required multiplexing in non-intuitive ways.

They can require a variety of driving voltages and current. The drive circuit will depend on which array you're using.

If you can provide a link to the LED arrays you plan to use, it would help people replying to your questions.

• Posts: 9
"Your diagram shows the led matrix as a single lamp, but the matrix leds are an array of 64 leds connected in 8 rows x 8 columns. If you want to use the matrix as a single lamp you will need a current limiting resistors on each of the rows or columns. Assuming the resistors are connected to the rows you will connect the +V to all the resistors and -V to all the columns." Yes, I do want the 8x8 matrixes to light as one. I did realize the diagram shows a single LED; it's just the only diagram I have. One single LED will not be bright enough for viewing at a distance.
All your other comments are very much appreciated and answer most of my questions. I'm a novice, but I am pretty sure that the 8x8 common anode or cathode would be the proper choice.(only an assumption) If you are interested in 'completing' my diagram, I'd be happy to donate a fee.
As far as the power supply, the diagram shows a 12v supply. I assumed this could be changed to supply the requirements of the 8x8 matrixes and the resistors.
• Posts: 9
Duane Degn,
Thanks for your reply. I think (assume) that the common anode or common cathode type is the correct one for my use. I'm basing that assumption on the assumption that those are "simpler" and will light all at once, with the correct driver and resistors. I'm a novice at this and was assuming that the ULN 2003 driver was adequate. I did notice that I can buy 8x8 matrixes mounted on a board[enclosed file] that use another driver [MAX7219 driver] but that is not the simple ULN 2003 driver.
Any completion of my diagram, using the 8x8 matrixes (because I need the lights to be very "visible" at 25 to 30 feet ) will be greatly appreciated. The entire project will be mounted in a long, rectangular box (about 14 inches long)
• Posts: 10,543
because I need the lights to be very "visible" at 25 to 30 feet

What sort of lighting will be they be used with? Is it a bright room? Outdoors in the sun?

How long do they need to be on at a time and how long total does the battery need to last? Can you use a car battery?

How do will you control the LEDs? Do you just want a button or switch?

Is there a reason you want to use the ULN2003 driver or is it just a driver you saw in an example circuit?

8x8 arrays are a lot of fun but they're generally used to display a pattern or text (or eyes). They're not really a great choice if you just want the light to be bright. There are certainly applications where have a LED array would be a good choice for visibility but depending on the specific application there may be easier and better options.

I just searched Amazon for "green LED" and a bunch of options came up.
Here's a bunch of LEDs which run on 12V and include resistors. There are plenty of other options like this one for cars.

I wouldn't use the 8x8 array in this application unless you like the way it looks. There are other options which would likely be brighter and easier. It's fine if you like the looks of the 8x8 arrays (I do myself).

Again a lot comes down to how you want to control the lights.

• Posts: 8,697
............

If you are interested in 'completing' my diagram, I'd be happy to donate a fee.
As far as the power supply, the diagram shows a 12v supply. I assumed this could be changed to supply the requirements of the 8x8 matrixes and the resistors.

Your project is relatively straight forward so I will help you, no fee required. Just buy the individual 8x8 led matrix displays and let me know which ones you choose. Common anode or cathode will work, you just need ones bright enough for your application. The other thing I will need to know is if one or more of the 8x8 led displays will be on at the same time. For driving the displays I would suggest using a ULN2803 instead of the ULN2003. The 2803 has 8 drivers, allowing us to use 2 per display.
• Posts: 9

How long do they need to be on at a time and how long total does the battery need to last? Can you use a car battery?

How do will you control the LEDs? Do you just want a switch or button"
The extension lights are controlled by a TLL in another box, via the round 6 position DIN. The LEDs only come on momentarily (programmed by the TLL, maybe a second, but long enough to observe. The lights on the main unit are single and are not easy to see - I think they even may be white as the enclosure box has a red and a green "lens" to amplify the LED. (I'd have to look.
Even a 12v adaptor would likely work but my diagram doesn't show anything but a 12v line in or how this would be included on the board. The extension LED box would be used no more than 5 hours in our application. No buttons or switches are required other than disconnecting the power source - so maybe a plug-in 12v adaptor might be easier.
Since this extension LED project is a signaling unit, it needs to be highly visible - the designers of the original TLL signaling unit made this DIN plug provision for just this reason, e.g. lights not very visible in a large venue from many angles. A 8x8 array is used in other, (much more expensive, commercially available extension light boxes) that is why I wanted them. My intention here is too do this project inexpensively - there are applicable units but they cost hundreds of dollars. Since I'm purchasing the materials here in Thailand, my (so far) projected costs seem to be about \$60.00. I'm retired so my time is not a factor.

• Posts: 9

kwinn,
That sounds fantastic. I have the tools and good soldering skills but as I said not much theoretical knowledge of these circuits. As you will read in my posts with Duane Degn, a 12v (or larger plug-in adaptor may be a better choice than batteries.
Two 8x8 arrays can light at the same time (controlled by the TLL main unit) momentarily, but only for a second or slightly longer. The arrangement on the enclosure box is a red array on the left and green on the right, with a white array under each color. Any array can light separately or both colors or both whites or a color and a white (all controlled by the TLL) Never more than 2 arrays at one time.
I did suspect that the ULN2003 was just for the single LED's I will find the Digikey part numbers and post some options to you on the arrays. I think I can get everything from Digikey Thailand - resistors, arrays, plugs, adaptor sockets and they have a nice ABS box about 14 inches long, that should have room for the arrangement of the *x8 arrays.
Thanks for your interest.

• Posts: 9
kwinn,
I have the Digikey part numbers for the "Adafruit" brand matrixes.
The amber LED will work for red but I can tint it if it doesn't look right. I do have the pdf datasheets but it's not obvious to me how to get them on here without a "file" button. New posts have this but not this reply.
part numbers:
amber 1528-2226ND
green 1528-2228ND
white 1528-1953ND
If this isn't sufficient info, I'll figure out how to send the pdf files. If you decide these lights are applicable, I'll order them (and any other parts you suggest)
• Posts: 8,697
........

If this isn't sufficient info, I'll figure out how to send the pdf files. If you decide these lights are applicable, I'll order them (and any other parts you suggest)

This is fine, part numbers are all I really need. Already downloaded the data sheets.
• Posts: 8,697
Attached a simple block diagram of the circuit.
The 555 timer and 74HC2017 could be replaced with a small microcontroller with 8 I/O's if you prefer.
Can you tell me what the voltage is that turns the current lamps on and off?
What supply voltages are available in the existing hardware?
• Posts: 8,697
Oops
• Posts: 9
kwinn,
I'll get back to you very shortly. I'll send a more detailed description of the unit that this extension light project is controlled by. Might take a day or two.
• Posts: 9

kwinn,

Sorry to take so long getting back to this. Enclosed file is the original unit that will send the signal to the extension LEDS. This is powered by a switching adaptor 12v/2.0 A output operating from 240v power [Thailand] 50-60Hz 0.3 A

The board is 3.5 inch x 7 inch on the original unit.

I had to choose some different LED matrix - (lead ordering time just too long) but the new one I ordered are 8x8- 6mm square dot /common anode in white, red and jade green, and will arrive in about a week. If you need exact info about them, I will take photos or they may have other spec s printed on them or shipped with them. The required switching adaptor, is a question, since the manufacturer of the original device did advise that their unit does not supply enough power for extension LED's

I am assuming I will need a larger, generic PCB with the outside holes for the DIN socket and switching adaptor and the smaller pitch for the resistors and LED's? I'm not sure what pitch is required for the other components you showed in your diagram. So advice on the proper board will be appreciated.

The ULN 2803A, the board mount 8 position DIN socket, plugs to match and enclosure box, I can get right away. Resistors should be no problem locally as well.

The other parts you show, I'm not familiar with, ["555" and 74HC4017] so generic descriptions/or part numbers will help (DigiKey has long lead times on many items , but glad that they show in stock availability.

• Posts: 9

kwinn,

The 555 is a part number for the generic board?

The 74HC4017 - a timer? There are many Diigikey part numbers with a large choice of suffix letters -any specific suggestions?

As soon as I get the lights in my hands, I'll let you know the forward voltage and I'm assuming (again) that I'll use a 12v dc adapter for the supply power. Hope this will be enough to decide the resistor values

• Posts: 8,697

The 555 is an oscillator/timer IC, and has a variety of suffixes. ne555t, se555, etc. The 74HC4017 is a counter with 10 outputs. It will be clocked by the 555 and wired so it only steps through 8 of the 10 outputs so each row of the led matrix will be multiplexed (powered in turn). We may need an on board regulator to supply +5V. You will also have to determine the voltage of the 4 signals (currently marked as ?) that power the existing lamps and use them to turn the led matrix displays on.

Are you having a PCB made for this or using a pad per hole perf board? The circuit is simple enough for perf board construction as long as you use parts that come in dip packages.