Progressive shift light for a racecar. - Page 1
Forum section: electronics / projects

author: A.Huggy
author_rank: Contributor
timestamp: November 12, 2016, 11:00:12 pm
content: I've been documenting this project on a car forum for a month or two, and I think they are getting tired of all of the electronics talk, so I'm going to port my documentation over here where it might be more useful.A company called Ecliptic sells a product known as the Shift-i. It's basically a consumer version of the progressive shift lights you see in race cars, as the engine revs, a bank of LED's start lighting up, when the engine approaches max RPM or the optimal shift point, the LED's all flash. My family runs a race team for a really amateur series and we have one in our racecar:It's really cool, but it has some quirks that I always thought I could improve upon. Also, this product seems to be discontinued and even when it was widely available, it was $150. I'm sure it was a fair price, but a bit hard to justify unless you need it for a competition application. I wanted one for my weekend toy (Mazda Miata), so I figured I would throw one together using an Arduino, jellybean parts, a button, and some WS2812b RGB LED's.This is the circuit I used to convert the 12v tach signal from the car into a 5v square wave the arduino could read:I probably could use a voltage divider, but I feel like this offers a little more protection to the arduino if any strange things happen in the car's electrical system.Here's a picture and a schematic of the arduino setup:It works great!This is where my first post about the project on the car forum left off. I got a lot of interest and a few PM's from other users asking for me to build one for them. I'm just a student that threw some parts on a breadboard, so I turned them down, but I did eventually realize that this might offer a good opportunity to pretend as if I was going to develop a product.I put together a more durable prototype and installed it in the Honda Civic that I drive everyday.After school over the next few weeks I used CM and Creo to layout my first board and find an enclosure that would look decent.I'm using an ATTiny85 for the micro controller and the LM1117 as a 5v supply. The same NPN circuit from above is being used to translate the tach signal. It's a really simply board. I included some extra parts and a USB port to allow for the ATTiny to be programmed on the fly, but this turned out to be more trouble than it's worth. I made good use of the EEPROM and the button in the design to allow the device to be user programmable. You can set what RPM the LED's start turning on, and at what RPM they start flashing.About a month later, I had boards on hand.I was surprised when I assembled the first board and programmed the first ATTiny85 and the darn thing worked! My first board design and I got it first try. Huge confidence boost.I don't have a very good soldering iron, just a WLC100. It's not regulated and the tips are junk. So I tried my hand at applying solder paste and baking the boards in an old toaster.This has proven to be an easy and successful way of assembling these boards. I have made several of them and given them away to friends for feedback. So far so good. There are a few bugs, but all of the shift lights are still functional and the users like them after a few weeks of testing them for me.I'm not sure where to go next. I don't have the time to sell these things, I don't think they would be worth selling anyway, but it has been fun to learn about some of the steps involved in designing a product. I know there are improvements to be made, such as replacing the LM1117 with something designed for automotive use, but apart for that I'm not sure what I should change if I order another batch of boards. I'm open to suggestions.Thanks for reading.Edit: here's the schematic of the board pictured:

author: Vgkid
author_rank: Super Contributor
timestamp: November 13, 2016, 02:14:37 am
content: Nice job, haven't watched the videos yet. From what i've seen with automotive requirements, added protection is a plus.

author: kc8apf
author_rank: Regular Contributor
timestamp: November 13, 2016, 02:19:38 am
content: Awesome! I'm really glad to see another gearhead designing electronics. I like the form factor and simplicity. I suspect selling on Tindie would be fairly painless.Please post a schematic. That will help with understanding your design and what could be problematic.Sent from my K88 using Tapatalk

author: A.Huggy
author_rank: Contributor
timestamp: November 13, 2016, 09:09:40 pm
content: I'll edit the original post and include the original schematic.Here's what I'm thinking for the next revision:

author: kc8apf
author_rank: Regular Contributor
timestamp: November 15, 2016, 07:08:31 am
content: A few unorganized thoughts:Dropping 12V to 5V with an LDO can generate alotof heat. You might consider a switching regulator instead.Automotive 12V floats with the charging system, is usually noisy, and can experience huge transients. I suggest adding overvoltage protection and possibly some filtering on the 12V input.When you plug in a USB cable, you are backfeeding the 5V LDO which is bad practice. Add a diode.If you accidentally connect the 6-pin header rotated 180 deg, you'll connect 12V to the 5V rail. Either split into 2 connectors (one for inputs and one for outputs), change the pinout so an accident won't work but also won't blow up devices, or use a keyed connector.

author: CJay
author_rank: Super Contributor
timestamp: November 15, 2016, 10:04:15 am
content: Very nice, bear in mind that there are companies selling almost this exact product so that's proof positive there's a market, now you have to work out if you can get into that market and make a profit.Lots of scope for expansion too so:Added value, maybe an RTC or some sort of timer to timestamp RPM data logging?If you've enough space in the code memory, perhaps you could incorporate code for one of the tilt/pitch/yaw sensors used by the quadcopter guys to give an idea of cornering forces, acceleration, deceleration in that log file (raw numbers, Excel or a PC app could do the maths)?You could possibly even add GPS at some point in the future, that way you could tie down the data to specific corners on a track...

author: Brutte
author_rank: Frequent Contributor
timestamp: November 15, 2016, 01:45:54 pm
content: QuoteThe diode (D2) is reverse biassed. Always. Well, perhaps except the situation when the tach signal dives <-0.7V below Car's GND. Or is D2 a zener diode?If you want to tie 12V signal to avr then just use a resistor divider.

author: RobertBG
author_rank: Regular Contributor
timestamp: November 15, 2016, 08:32:41 pm
content: Nice workAs others have said there's still a few people selling these but not too many and for way too much $$.Now I know you mentioned you dont want to manufacture them for sale.But if I were you I'd seriously contemplate offering it as a kit form.With a little refinement you have a nice little product and offering kits will save a lot of headaches yet still offer a nice return for the time invested.As a gear head myself,I'd never spend close to $100+ for one but if I saw a nice kit I could use or modify I'd probably jump at it.I have a few things I sell in both kits and complete units for the performance marine world.But we started mainly with kits and for us they are the most profitable.Good luck and feel free to PM me if you think about offering a kit as I could see this working with the stuff I offer

author: kc8apf
author_rank: Regular Contributor
timestamp: November 16, 2016, 12:31:14 am
content: Quote from: Brutte on November 15, 2016, 01:45:54 pmIf the tach pin is disconnected (HiZ), the diode prevents the base from floating.Sent from my Nexus 5X using Tapatalk

author: Brutte
author_rank: Frequent Contributor
timestamp: November 16, 2016, 09:06:37 am
content: Quote from: kc8apf on November 16, 2016, 12:31:14 amD2 starts conducting only when Ube goes below -0,6V and that won't happen if tach pin is disconnected (HZ).

author: hans
author_rank: Super Contributor
timestamp: November 16, 2016, 11:44:23 am
content: I would certainly add some protection to the 12V line. Reversed polarity, negative voltage transients, etc. are quite common on automotive buses. Some are common, like spikes from solenoids (windscreen wipers), others very rare like disconnecting battery while the alternator is charging, or reversing battery terminals with a jumpstart.There are ISO standards for that (e.g. ISO7637) , but usually a reverse protection FET/diode, poly fuse and TVS will do well. The worst cases of linked table is questionable whether you want your product to survive that, it's usually the case I described with disconnecting battery, and that's usually a serious electrical fault or human error.Also note, the table describes only peak voltages and no source impedance. Some spikes seem absurpt, but only describe peak value. You may want to look for hints of manufacturers that advertise components for certain test pulses, or hunt for the ISO document itself (which unfortunately is not free).