Need opinions on a project. - Page 1
Forum section: electronics / projects

author: jknightandkarr
author_rank: Contributor
timestamp: November 13, 2020, 06:59:16 am
content: I really need help on this project. I have found common cathode bi-color bargraph leds fount here:https://www.sunledusa.com/products/spec/XGURUGX10D.pdfand am trying to make a voice display like in the original knight rider. I've made my patterns with no issues for both KITT, the schematics with the red lines and KARR, only in 2 episodes, with the green lines. now the leds are common cathode and I've figured out how to make them work, I think, but I have questions. Now I am using 2 pcbs that will ultimately be touching and soldered to the leds, sorta like a 4 layer board, the main one, in my case I just made KARR's pattern and a smaller one that will be directly touching the backside of the main board, only connected by the 6 bargraph leds, 2 power pins, power only one or other to choose the desired display and a 10 pin connector that will ultimately be controlled via an LM3914 driver IC. Now here's my question. On both boards there will be a separate set of resistors and diodes for each color on the CC side to adjust the brightness since KARR's display just uses 8 same value resistors and KITT's uses 3 different values, first 2 are for 2 leds then 6 for 6 leds then finally 2 more resistors for 4 leds, so I can't put the resistors on a different board. I've placed diodes between the resistors and the 10 pin connector. Now I know that unless both v+ pins are powered, only one set will work either red or green, but since the commons at the connector are connected is there any way that the other non-powered pcb would make the patterns mess up. Ex: KITT's 1st of 10 in the display come on like KARR's 1st of 8 in that pattern, (KARR's display doesn't use all 10 pins on the 3914)? Meaning instead of the desired very center 2 red leds being powered on, I'd get the center red on but also the remaining 4 bargraphs both very tops and very bottoms. I've added an image of the voice box designs, basically KITT's might start out to look like the green display instead or other not desired leds on? I am just a hobbyist and while I've got schematics of the voice boxes, just not combined like I am trying to-do, so I know the general idea of how they've been built before works. Due to the design of my to use leds, it is not possible use them on bread boards, I'd literally need to make a pcb, and since i really don't have much money, spending uneeded cash on boards that I'd have multiple of just to find out it won't work isn't desired, nor is making my own boards as I've never had luck on that. Any input is appreciated, on.Edit: On the schematics, both circuits use the same set of 6 leds and 10 pin connector, I just made them 2 different ones due to pattern differences and to make them easier to read and edit. Also due to space limits of the circuit boards, I don't see how I could make a true 4 layer design, so that's why I am soldering 2 boards directly to the same set of pins.

author: jknightandkarr
author_rank: Contributor
timestamp: November 15, 2020, 01:05:41 pm
content: Anyone? I really can't build the circuit on breadboard to test for issues on this and i really don't wanna spend $56 just to find out my design won't work. Can't afford it.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: November 15, 2020, 08:30:24 pm
content: I didn't understand anything... But it is not a good idea to connect several LEDs in parallel to a single resistor . The onboard voltage in a car is sufficiently high to enable the LEDs to be switched on in series.

author: bson
author_rank: Unknown
timestamp: November 15, 2020, 09:02:24 pm
content: How about an actual schematic, with resistor values, supply voltages, and the LED assemblies. Not just some package-focused rat's nest...

author: Renate
author_rank: Super Contributor
timestamp: November 15, 2020, 10:33:52 pm
content: First, why are you using bi-color LEDS and not even wiring up both diodes? That's crazy.You can get (single color) 10 segment bar graphs in every color. And they have a normal footprint that you can even breadboard.Doing two separate board layouts for Mr Red & Ms Green is even more work. Just do one layout.Having the 2 LED offset on Mr Red is limiting too.At the very least, have 16 active lines for a display, the two outside columns ( 8 ) and the inside column ( 8 ).I mean, you might get bored by the limited possibilities and want to play Pong.If you're going for non-multiplexed then you don't need any isolation diodes there.And if you are multiplexing then you don't need any isolation dioedes there.And, as pointed out, putting LEDs directly in parallel is a poor idea, one LED will hog more current.Multiplexing will keep your PCB layout really simple.8 x 6. Is 16% duty cycle bright enough for you?I realize that you want to keep this accurate and use 8 bars.8 bar segments would be a better fit but probably all the 8 bars are older, less efficient and less color choice than 10 bar.

author: phil from seattle
author_rank: Super Contributor
timestamp: November 15, 2020, 11:29:29 pm
content: OK, this is needlessly complex. A suggestion - get individual addressable LEDs like WS2812 (the kind they put on the flexible strips). You can pack them tightly on a PCB and use a diffuser with scribed lines to create the right effect. Then, you really just need one pin (maybe 2 pins) to control them. The big advantage is you can set the color in software so layout is the same for either. They are SMD chips but are about as easy as it gets to solder. And they aren't that expensive though you might need to order from China - last time I looked US distis didn't carry. You can test the idea out with the addressable light strips.

author: jknightandkarr
author_rank: Contributor
timestamp: November 19, 2020, 05:32:25 pm
content: Thanks for the replies.Quote from: S. Petrukhin on November 15, 2020, 08:30:24 pmI will try and see what I can do making them wired in serial, but I know I don't have too much room at all, but will try.Quote from: bson on November 15, 2020, 09:02:24 pmI did it that way due to keep it neat and easier for me to read. i had to make it easy to make the displays correct.Quote from: Renate on November 15, 2020, 10:33:52 pmThere are a few people out there who make the voice displays now, but they all use the single color bargraph LED's to make the VU meter displays, so I want to try, and make a display for both versions at the same time. The fiberglass dashes these are in aren't easy to work on unless they're out of the car. So changing out the voice display means a but job, i am just wanting to make it easier for people who like both versions of the display. as far ans being bored goes, all of the dashes either have 1 or 2 tv's or monitors, depending what season of the show that they are going for to use for whatever, so in my case I'll have an Xbox One installed in my car. lolQuote from: phil from seattle on November 15, 2020, 11:29:29 pmIt's a good ideas for displays, but in a case like this and the community I am a part of, people, some ALOT more then others, who demand parts having a few qualities: 1) They look good and match the show as far as literally possible. 2)In case of electronics function as much as possible to the show, even using computers or portable devices to add an AI of sorts to their cars. and the last 2 I could post but not really valid on my point, so I will skip those 2.i have literally seen posts where someone does something different, like they paint their replica say red and people replay with stuff like, "Nice buts it's not KITT or KARR..." or some have gone as far as saying hate like stuff that gets them instantly banned, so matching the show is a MUST, but i do like the general concept of your idea, I can always use the idea for something like the season 3/4 lower console that used lenses in the console that just light up. Would be good if someone wanted their lower console display to randomly flash or something like that. Will keep it in mind.Aaaaaand after looking over my designs put into the same file, they won't work.. The 2 sets of connections at the common pins on the LED's will just both connect together and undesired patterns will result, so going to separate and try and drive the displays using PNP transistors and LM3914 driver on the positive side instead of the ground side.

author: Renate
author_rank: Super Contributor
timestamp: November 19, 2020, 06:47:13 pm
content: Oh, I misread your schematic. I thought that you were showing two separate projects on one page.I'd still at least multiplex this.6 cathode drivers and 16 anode drivers.Don't even acknowledge that two LED offset for KITT in hardware, do it in software.It would just make your layout more difficult.Breadboard this with 16% duty cycle and see what resistors you need and how you like the brightness.

author: james_s
author_rank: Super Contributor
timestamp: November 19, 2020, 07:28:57 pm
content: In the future, if you break up your post into paragraphs it's much easier to read and follow than one huge monolithic block of text. This sounds like it should be a fairly trivial project but I'm not entirely clear on what the question is. Driving a bunch of LEDs from a microcontroller is a very common application, variations of which have been done many times before.