LED Speedometer  - Page 1
Forum section: electronics / projects

author: supercar14
author_rank: Newbie
timestamp: October 15, 2015, 06:53:07 am
content: Let me first say that I know there will be problems with this project. I'm still a beginner in this hobby and I've pretty much taught myself everything I know about it. I've made a dozen projects or so so far, but this is the only one I'd consider “finished” enough to actually show and possibly even eventually build. That being saidThe design for this came from a few schematics I found on the internet and frankenstiened them together with some of my own personal touches. The PCB design itself however was completely my design, so while I can't take full credit for the entire project at least I can for the PCB. Anyway, the gauge has a 5” diameter and the basic idea is the outer ring of leds is for the numbers while the inner ring progressively lights up in place of a needle with a 0-145 mph range (assuming I did my math right, I probably didn't). I'm planning on having a plastic gauge face that goes over the board that isolates each led and screws through the back of the pcb through the four mounting holes. I'll likely change that a bit, probably by removing some of the leds for the numbers and linking the rest together somehow.The circuit works with three LM3914 dot bar drivers cascaded together. I used a LM2917 frequency to voltage converter to take the input signal from the VSS (vehicle speed sensor for those you not familiar with cars). The original design didn't use this and somehow rigged a stepper motor from a printer as the sensor rather than use a dedicated VSS. This is wedged in where it is because I only realized I needed it after I'd already finished the PCB... oops... That's also why it's on a separate page on the schematic. Although I said it was finished I still have more to do to it. Like clean up the schematic a bit and I've been thinking of changing the wiring on the LM3914s among other things. Also I wouldn't even begin to know how to accurately calibrate it without it actually being built up since the signal would be different depending on what type of VSS I used and how it was setup.I couldn't get KiCad to cooperate and export a picture of the PCB so I just took some screenshots, sorry if they're hard to see. I can take some more closer to certain areas if anyone wants to see them. I also included a picture with the ground plane removed so the components and traces are easier to see.So what to you guys think? Love it? Hate it? Let me know what I can do to improve it!

author: NEYi
author_rank: Contributor
timestamp: October 15, 2015, 11:14:34 am
content: A nice beginner project if you ask me.A bit old-style, though. You won't see a lot of people making stuff with LM3914 these days.Assemble this thing up and start learning MCUs, you definitely won't regret it.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: October 16, 2015, 03:19:40 am
content: It's a beautifully simple and straightforward analog design! Make it so!But for a more modern, digital concept, one might consider using NeoPixel LEDs (WS2812) and MCU. Just think... the LEDs could easily change color and brightness, etc. and would need simpler PCB construction since all of them could be controlled with only a single data line and the two power lines.

author: promacjoe
author_rank: Regular Contributor
timestamp: October 16, 2015, 04:25:25 am
content: The TM1638 is a one chip solution for the LED drivers, It can control both the individual LED, and the 4 digit seven segment LED display, at the same time with brightness control. The chip also gives you a 3 x 8 keyboard inputs. All using a SPI interface. the chip can Control a 8x10 LED matrix, or up to 10 seven segment LED displays with decimal. and it is very inexpensive and easy to use. There are several videos on using this chip with the Arduino platform on youtube, including a digital speedometer, connected to a computer game.

author: supercar14
author_rank: Newbie
timestamp: October 22, 2015, 05:36:01 am
content: Sorry for the last response, I've been busy lately. Thanks for the replies you guys. I could say that the reason I'm not using MCs is that I just like that old analog stuff. Which I do trust me. I drive a 65 Mustang and I like to work on older cars because at least to me it's so much more satisfying to just be able to get your tools and just fix something without having to worry about fiddling with sensors and error codes and computers etc... I feel the same about electronics too... I could say all that but the real reason is... I really really really suck at programming. Anything more advanced than the most basic beginners programs just looks like Swahili to me. I'm sure that with enough practice I'll get the hang of it and I'll love it once I do, but for now... Well I've been told nothing worth doing was ever easy. Anyway thanks again for the replies.Cheers

author: richard.cs
author_rank: Super Contributor
timestamp: October 22, 2015, 07:21:12 am
content: Quote from: NEYi on October 15, 2015, 11:14:34 amMaybe not often but I have used them in a £60k project at work to indicate received signal strength (working from receiver's AGC line). This was in a demonstrator unit that was delivered to the customer. It did actually have a micro with access to the same information but the 3914 was more useful as it didn't have aliasing problems and didn't freeze when the micro was running time critical code.

author: tron9000
author_rank: Frequent Contributor
timestamp: October 22, 2015, 07:50:29 am
content: I like it!Simple - which is always good, junk-box parts makes it low cost and easily constructed. Love to see it working.